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2024-11-20Merge tag 'printk-for-6.13' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux Pull printk updates from Petr Mladek: - Print more precise information about the printk log buffer memory usage. - Make sure that the sysrq title is shown on the console even when deferred. - Do not enable earlycon by `console=` which is meant to disable the default console. * tag 'printk-for-6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: printk: add dummy printk_force_console_enter/exit helpers tty: sysrq: Use printk_force_console context on __handle_sysrq printk: Introduce FORCE_CON flag printk: Improve memory usage logging during boot init: Don't proxy `console=` to earlycon
2024-11-18Merge branch 'for-6.13-force-console' into for-linusPetr Mladek
2024-11-11printk: Introduce FORCE_CON flagMarcos Paulo de Souza
Introduce FORCE_CON flag to printk. The new flag will make it possible to create a context where printk messages will never be suppressed. This mechanism will be used in the next patch to create a force_con context on sysrq handling, removing an existing workaround on the loglevel global variable. The workaround existed to make sure that sysrq header messages were sent to all consoles, but this doesn't work with deferred messages because the loglevel might be restored to its original value before a console flushes the messages. Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com> Reviewed-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Link: https://lore.kernel.org/r/20241105-printk-loud-con-v2-1-bd3ecdf7b0e4@suse.com Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-11-05seqlock, treewide: Switch to non-raw seqcount_latch interfaceMarco Elver
Switch all instrumentable users of the seqcount_latch interface over to the non-raw interface. Co-developed-by: "Peter Zijlstra (Intel)" <peterz@infradead.org> Signed-off-by: "Peter Zijlstra (Intel)" <peterz@infradead.org> Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20241104161910.780003-5-elver@google.com
2024-10-16printk: Improve memory usage logging during bootIsaac J. Manjarres
When the initial printk ring buffer size is updated, setup_log_buf() allocates a new ring buffer, as well as a set of meta-data structures for the new ring buffer. The function also emits the new size of the ring buffer, but not the size of the meta-data structures. This makes it difficult to assess how changing the log buffer size impacts memory usage during boot. For instance, increasing the ring buffer size from 512 KB to 1 MB through the command line yields an increase of 2304 KB in reserved memory at boot, while the only obvious change is the 512 KB difference in the ring buffer sizes: log_buf_len=512K: printk: log_buf_len: 524288 bytes Memory: ... (... 733252K reserved ...) log_buf_len=1M: printk: log_buf_len: 1048576 bytes Memory: ... (... 735556K reserved ...) This is because of how the size of the meta-data structures scale with the size of the ring buffer. Even when there aren't changes to the printk ring buffer size (i.e. the initial size == 1 << CONFIG_LOG_BUF_SHIFT), it is impossible to tell how much memory is consumed by the printk ring buffer during boot. Therefore, unconditionally log the sizes of the printk ring buffer and its meta-data structures, so that it's easier to understand how changing the log buffer size (either through the command line or by changing CONFIG_LOG_BUF_SHIFT) affects boot time memory usage. With the new logs, it is much easier to see exactly why the memory increased by 2304 KB: log_buf_len=512K: printk: log buffer data + meta data: 524288 + 1835008 = 2359296 bytes Memory: ... (... 733252K reserved ...) log_buf_len=1M: printk: log buffer data + meta data: 1048576 + 3670016 = 4718592 bytes Memory: ... (... 735556K reserved ...) Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com> Reviewed-by: Petr Mladek <pmladek@suse.com> Tested-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240930184826.3595221-1-isaacmanjarres@google.com [pmladek@suse.com: Updated the examples in the commit message, simplified comment for default buffer.] Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-19Merge tag 'drm-next-2024-09-19' of https://gitlab.freedesktop.org/drm/kernelLinus Torvalds
Pull drm updates from Dave Airlie: "This adds a couple of patches outside the drm core, all should be acked appropriately, the string and pstore ones are the main ones that come to mind. Otherwise it's the usual drivers, xe is getting enabled by default on some new hardware, we've changed the device number handling to allow more devices, and we added some optional rust code to create QR codes in the panic handler, an idea first suggested I think 10 years ago :-) string: - add mem_is_zero() core: - support more device numbers - use XArray for minor ids - add backlight constants - Split dma fence array creation into alloc and arm fbdev: - remove usage of old fbdev hooks kms: - Add might_fault() to drm_modeset_lock priming - Add dynamic per-crtc vblank configuration support dma-buf: - docs cleanup buddy: - Add start address support for trim function printk: - pass description to kmsg_dump scheduler: - Remove full_recover from drm_sched_start ttm: - Make LRU walk restartable after dropping locks - Allow direct reclaim to allocate local memory panic: - add display QR code (in rust) displayport: - mst: GUID improvements bridge: - Silence error message on -EPROBE_DEFER - analogix: Clean aup - bridge-connector: Fix double free - lt6505: Disable interrupt when powered off - tc358767: Make default DP port preemphasis configurable - lt9611uxc: require DRM_BRIDGE_ATTACH_NO_CONNECTOR - anx7625: simplify OF array handling - dw-hdmi: simplify clock handling - lontium-lt8912b: fix mode validation - nwl-dsi: fix mode vsync/hsync polarity xe: - Enable LunarLake and Battlemage support - Introducing Xe2 ccs modifiers for integrated and discrete graphics - rename xe perf to xe observation - use wb caching on DGFX for system memory - add fence timeouts - Lunar Lake graphics/media/display workarounds - Battlemage workarounds - Battlemage GSC support - GSC and HuC fw updates for LL/BM - use dma_fence_chain_free - refactor hw engine lookup and mmio access - enable priority mem read for Xe2 - Add first GuC BMG fw - fix dma-resv lock - Fix DGFX display suspend/resume - Use xe_managed for kernel BOs - Use reserved copy engine for user binds on faulting devices - Allow mixing dma-fence jobs and long-running faulting jobs - fix media TLB invalidation - fix rpm in TTM swapout path - track resources and VF state by PF i915: - Type-C programming fix for MTL+ - FBC cleanup - Calc vblank delay more accurately - On DP MST, Enable LT fallback for UHBR<->non-UHBR rates - Fix DP LTTPR detection - limit relocations to INT_MAX - fix long hangs in buddy allocator on DG2/A380 amdgpu: - Per-queue reset support - SDMA devcoredump support - DCN 4.0.1 updates - GFX12/VCN4/JPEG4 updates - Convert vbios embedded EDID to drm_edid - GFX9.3/9.4 devcoredump support - process isolation framework for GFX 9.4.3/4 - take IOMMU mappings into account for P2P DMA amdkfd: - CRIU fixes - HMM fix - Enable process isolation support for GFX 9.4.3/4 - Allow users to target recommended SDMA engines - KFD support for targetting queues on recommended SDMA engines radeon: - remove .load and drm_dev_alloc - Fix vbios embedded EDID size handling - Convert vbios embedded EDID to drm_edid - Use GEM references instead of TTM - r100 cp init cleanup - Fix potential overflows in evergreen CS offset tracking msm: - DPU: - implement DP/PHY mapping on SC8180X - Enable writeback on SM8150, SC8180X, SM6125, SM6350 - DP: - Enable widebus on all relevant chipsets - MSM8998 HDMI support - GPU: - A642L speedbin support - A615/A306/A621 support - A7xx devcoredump support ast: - astdp: Support AST2600 with VGA - Clean up HPD - Fix timeout loop for DP link training - reorganize output code by type (VGA, DP, etc) - convert to struct drm_edid - fix BMC handling for all outputs exynos: - drop stale MAINTAINERS pattern - constify struct loongson: - use GEM refcount over TTM mgag200: - Improve BMC handling - Support VBLANK intterupts - transparently support BMC outputs nouveau: - Refactor and clean up internals - Use GEM refcount over TTM's gm12u320: - convert to struct drm_edid gma500: - update i2c terms lcdif: - pixel clock fix host1x: - fix syncpoint IRQ during resume - use iommu_paging_domain_alloc() imx: - ipuv3: convert to struct drm_edid omapdrm: - improve error handling - use common helper for_each_endpoint_of_node() panel: - add support for BOE TV101WUM-LL2 plus DT bindings - novatek-nt35950: improve error handling - nv3051d: improve error handling - panel-edp: - add support for BOE NE140WUM-N6G - revert support for SDC ATNA45AF01 - visionox-vtdr6130: - improve error handling - use devm_regulator_bulk_get_const() - boe-th101mb31ig002: - Support for starry-er88577 MIPI-DSI panel plus DT - Fix porch parameter - edp: Support AOU B116XTN02.3, AUO B116XAN06.1, AOU B116XAT04.1, BOE NV140WUM-N41, BOE NV133WUM-N63, BOE NV116WHM-A4D, CMN N116BCA-EA2, CMN N116BCP-EA2, CSW MNB601LS1-4 - himax-hx8394: Support Microchip AC40T08A MIPI Display panel plus DT - ilitek-ili9806e: Support Densitron DMT028VGHMCMI-1D TFT plus DT - jd9365da: - Support Melfas lmfbx101117480 MIPI-DSI panel plus DT - Refactor for code sharing - panel-edp: fix name for HKC MB116AN01 - jd9365da: fix "exit sleep" commands - jdi-fhd-r63452: simplify error handling with DSI multi-style helpers - mantix-mlaf057we51: simplify error handling with DSI multi-style helpers - simple: - support Innolux G070ACE-LH3 plus DT bindings - support On Tat Industrial Company KD50G21-40NT-A1 plus DT bindings - st7701: - decouple DSI and DRM code - add SPI support - support Anbernic RG28XX plus DT bindings mediatek: - support alpha blending - remove cl in struct cmdq_pkt - ovl adaptor fix - add power domain binding for mediatek DPI controller renesas: - rz-du: add support for RZ/G2UL plus DT bindings rockchip: - Improve DP sink-capability reporting - dw_hdmi: Support 4k@60Hz - vop: - Support RGB display on Rockchip RK3066 - Support 4096px width sti: - convert to struct drm_edid stm: - Avoid UAF wih managed plane and CRTC helpers - Fix module owner - Fix error handling in probe - Depend on COMMON_CLK - ltdc: - Fix transparency after disabling plane - Remove unused interrupt tegra: - gr3d: improve PM domain handling - convert to struct drm_edid - Call drm_atomic_helper_shutdown() vc4: - fix PM during detect - replace DRM_ERROR() with drm_error() - v3d: simplify clock retrieval v3d: - Clean up perfmon virtio: - add DRM capset" * tag 'drm-next-2024-09-19' of https://gitlab.freedesktop.org/drm/kernel: (1326 commits) drm/xe: Fix missing conversion to xe_display_pm_runtime_resume drm/xe/xe2hpg: Add Wa_15016589081 drm/xe: Don't keep stale pointer to bo->ggtt_node drm/xe: fix missing 'xe_vm_put' drm/xe: fix build warning with CONFIG_PM=n drm/xe: Suppress missing outer rpm protection warning drm/xe: prevent potential UAF in pf_provision_vf_ggtt() drm/amd/display: Add all planes on CRTC to state for overlay cursor drm/i915/bios: fix printk format width drm/i915/display: Fix BMG CCS modifiers drm/amdgpu: get rid of bogus includes of fdtable.h drm/amdkfd: CRIU fixes drm/amdgpu: fix a race in kfd_mem_export_dmabuf() drm: new helper: drm_gem_prime_handle_to_dmabuf() drm/amdgpu/atomfirmware: Silence UBSAN warning drm/amdgpu: Fix kdoc entry in 'amdgpu_vm_cpu_prepare' drm/amd/amdgpu: apply command submission parser for JPEG v1 drm/amd/amdgpu: apply command submission parser for JPEG v2+ drm/amd/pm: fix the pp_dpm_pcie issue on smu v14.0.2/3 drm/amd/pm: update the features set on smu v14.0.2/3 ...
2024-09-17Merge tag 'printk-for-6.12' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux Pull printk updates from Petr Mladek: "This is the "last" part of the support for the new nbcon consoles. Where "nbcon" stays for "No Big console lock CONsoles" aka not under the console_lock. New callbacks are added to struct console: - write_thread() for flushing nbcon consoles in task context. - write_atomic() for flushing nbcon consoles in atomic context, including NMI. - con->device_lock() and device_unlock() for taking the driver specific lock, for example, port->lock. New printk-specific kthreads are created: - per-console kthreads which get responsible for flushing normal priority messages on nbcon consoles. - thread which gets responsible for flushing normal priority messages on all consoles when CONFIG_RT enabled. The new callbacks are called under a special per-console lock which has already been added back in v6.7. It allows to distinguish three severities: normal, emergency, and panic. A context with a higher priority could take over the ownership when it is safe even in the middle of handling a record. The panic context could do it even when it is not safe. But it is allowed only for the final desperate flush before entering the infinite loop. The new lock helps to flush the messages directly in emergency and panic contexts. But it is not enough in all situations: - console_lock() is still need for synchronization against boot consoles. - con->device_lock() is need for synchronization against other operations on the same HW, e.g. serial port speed setting, non-printk related read/write. The dependency on con->device_lock() is mutual. Any code taking the driver specific lock has to acquire the related nbcon console context as well. For example, see the new uart_port_lock() API. It provides the necessary synchronization against emergency and panic contexts where the messages are flushed only under the new per-console lock. Maybe surprisingly, a quite tricky part is the decision how to flush the consoles in various situations. It has to take into account: - message priority: normal, emergency, panic - scheduling context: task, atomic, deferred_legacy - registered consoles: boot, legacy, nbcon - threads are running: early boot, suspend, shutdown, panic - caller: printk(), pr_flush(), printk_flush_in_panic(), console_unlock(), console_start(), ... The primary decision is made in printk_get_console_flush_type(). It creates a hint what the caller should do: - flush nbcon consoles directly or via the kthread - call the legacy loop (console_unlock()) directly or via irq_work The existing behavior is preserved for the legacy consoles. The only exception is that they are not longer flushed directly from printk() in panic() before CPUs are stopped. But this blocking happens only when at least one nbcon console is registered. The motivation is to increase a chance to produce the crash dump. They legacy consoles might create a deadlock in compare with nbcon consoles. The nbcon console should allow to see the messages even when the crash dump fails. There are three possible ways how nbcon consoles are flushed: - The per-nbcon-console kthread is responsible for flushing messages added with the normal priority. This is the default mode. - The legacy loop, aka console_unlock(), is used when there is still a boot console registered. There is no easy way how to match an early console driver with a nbcon console driver. And the console_lock() provides the only reliable serialization at the moment. The legacy loop uses either con->write_atomic() or con->write_thread() callbacks depending on whether it is allowed to schedule. The atomic variant has to be used from printk(). - In other situations, the messages are flushed directly using write_atomic() which can be called in any context, including NMI. It is primary needed during early boot or shutdown, in emergency situations, and panic. The emergency priority is used by a code called within nbcon_cpu_emergency_enter()/exit(). At the moment, it is used in four situations: WARN(), Oops, lockdep, and RCU stall reports. Finally, there is no nbcon console at the moment. It means that the changes should _not_ modify the existing behavior. The only exception is CONFIG_RT which would force offloading the legacy loop, for normal priority context, into the dedicated kthread" * tag 'printk-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: (54 commits) printk: Avoid false positive lockdep report for legacy printing printk: nbcon: Assign nice -20 for printing threads printk: Implement legacy printer kthread for PREEMPT_RT tty: sysfs: Add nbcon support for 'active' proc: Add nbcon support for /proc/consoles proc: consoles: Add notation to c_start/c_stop printk: nbcon: Show replay message on takeover printk: Provide helper for message prepending printk: nbcon: Rely on kthreads for normal operation printk: nbcon: Use thread callback if in task context for legacy printk: nbcon: Relocate nbcon_atomic_emit_one() printk: nbcon: Introduce printer kthreads printk: nbcon: Init @nbcon_seq to highest possible printk: nbcon: Add context to usable() and emit() printk: Flush console on unregister_console() printk: Fail pr_flush() if before SYSTEM_SCHEDULING printk: nbcon: Add function for printers to reacquire ownership printk: nbcon: Use raw_cpu_ptr() instead of open coding printk: Use the BITS_PER_LONG macro lockdep: Mark emergency sections in lockdep splats ...
2024-09-09printk: Export match_devname_and_update_preferred_console()Yu Liao
When building serial_base as a module, modpost fails with the following error message: ERROR: modpost: "match_devname_and_update_preferred_console" [drivers/tty/serial/serial_base.ko] undefined! Export the symbol to allow using it from modules. Reported-by: kernel test robot <lkp@intel.com> Closes: https://lore.kernel.org/oe-kbuild-all/202409071312.qlwtTOS1-lkp@intel.com/ Fixes: 12c91cec3155 ("serial: core: Add serial_base_match_and_update_preferred_console()") Signed-off-by: Yu Liao <liaoyu15@huawei.com> Link: https://lore.kernel.org/r/20240909075652.747370-1-liaoyu15@huawei.com Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: Avoid false positive lockdep report for legacy printingJohn Ogness
Legacy console printing from printk() caller context may invoke the console driver from atomic context. This leads to a lockdep splat because the console driver will acquire a sleeping lock and the caller may already hold a spinning lock. This is noticed by lockdep on !PREEMPT_RT configurations because it will lead to a problem on PREEMPT_RT. However, on PREEMPT_RT the printing path from atomic context is always avoided and the console driver is always invoked from a dedicated thread. Thus the lockdep splat on !PREEMPT_RT is a false positive. For !PREEMPT_RT override the lock-context before invoking the console driver to avoid the false positive. Do not override the lock-context for PREEMPT_RT in order to allow lockdep to catch any real locking context issues related to the write callback usage. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-18-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: nbcon: Assign nice -20 for printing threadsJohn Ogness
It is important that console printing threads are scheduled shortly after a printk call and with generous runtime budgets. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-17-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: Implement legacy printer kthread for PREEMPT_RTJohn Ogness
The write() callback of legacy consoles usually makes use of spinlocks. This is not permitted with PREEMPT_RT in atomic contexts. For PREEMPT_RT, create a new kthread to handle printing of all the legacy consoles (and nbcon consoles if boot consoles are registered). This allows legacy consoles to work on PREEMPT_RT without requiring modification. (However they will not have the reliability properties guaranteed by nbcon atomic consoles.) Use the existing printk_kthreads_check_locked() to start/stop the legacy kthread as needed. Introduce the macro force_legacy_kthread() to query if the forced threading of legacy consoles is in effect. Although currently only enabled for PREEMPT_RT, this acts as a simple mechanism for the future to allow other preemption models to easily take advantage of the non-interference property provided by the legacy kthread. When force_legacy_kthread() is true, the legacy kthread fulfills the role of the console_flush_type @legacy_offload by waking the legacy kthread instead of printing via the console_lock in the irq_work. If the legacy kthread is not yet available, no legacy printing takes place (unless in panic). If for some reason the legacy kthread fails to create, any legacy consoles are unregistered. With force_legacy_kthread(), the legacy kthread is a critical component for legacy consoles. These changes only affect CONFIG_PREEMPT_RT. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-16-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: nbcon: Show replay message on takeoverJohn Ogness
An emergency or panic context can takeover console ownership while the current owner was printing a printk message. The atomic printer will re-print the message that the previous owner was printing. However, this can look confusing to the user and may even seem as though a message was lost. [3430014.1 [3430014.181123] usb 1-2: Product: USB Audio Add a new field @nbcon_prev_seq to struct console to track the sequence number to print that was assigned to the previous console owner. If this matches the sequence number to print that the current owner is assigned, then a takeover must have occurred. In this case, print an additional message to inform the user that the previous message is being printed again. [3430014.1 ** replaying previous printk message ** [3430014.181123] usb 1-2: Product: USB Audio Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-12-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: Provide helper for message prependingJohn Ogness
In order to support prepending different texts to printk messages, split out the prepending code into a helper function. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-11-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: nbcon: Rely on kthreads for normal operationJohn Ogness
Once the kthread is running and available (i.e. @printk_kthreads_running is set), the kthread becomes responsible for flushing any pending messages which are added in NBCON_PRIO_NORMAL context. Namely the legacy console_flush_all() and device_release() no longer flush the console. And nbcon_atomic_flush_pending() used by nbcon_cpu_emergency_exit() no longer flushes messages added after the emergency messages. The console context is safe when used by the kthread only when one of the following conditions are true: 1. Other caller acquires the console context with NBCON_PRIO_NORMAL with preemption disabled. It will release the context before rescheduling. 2. Other caller acquires the console context with NBCON_PRIO_NORMAL under the device_lock. 3. The kthread is the only context which acquires the console with NBCON_PRIO_NORMAL. This is satisfied for all atomic printing call sites: nbcon_legacy_emit_next_record() (#1) nbcon_atomic_flush_pending_con() (#1) nbcon_device_release() (#2) It is even double guaranteed when @printk_kthreads_running is set because then _only_ the kthread will print for NBCON_PRIO_NORMAL. (#3) Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-10-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: nbcon: Use thread callback if in task context for legacyJohn Ogness
When printing via console_lock, the write_atomic() callback is used for nbcon consoles. However, if it is known that the current context is a task context, the write_thread() callback can be used instead. Using write_thread() instead of write_atomic() helps to reduce large disabled preemption regions when the device_lock does not disable preemption. This is mainly a preparatory change to allow avoiding write_atomic() completely during normal operation if boot consoles are registered. As a side-effect, it also allows consolidating the printing code for legacy printing and the kthread printer. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-9-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: nbcon: Relocate nbcon_atomic_emit_one()John Ogness
Move nbcon_atomic_emit_one() so that it can be used by nbcon_kthread_func() in a follow-up commit. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-8-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: nbcon: Introduce printer kthreadsThomas Gleixner
Provide the main implementation for running a printer kthread per nbcon console that is takeover/handover aware. This includes: - new mandatory write_thread() callback - kthread creation - kthread main printing loop - kthread wakeup mechanism - kthread shutdown kthread creation is a bit tricky because consoles may register before kthreads can be created. In such cases, registration will succeed, even though no kthread exists. Once kthreads can be created, an early_initcall will set @printk_kthreads_ready. If there are no registered boot consoles, the early_initcall creates the kthreads for all registered nbcon consoles. If kthread creation fails, the related console is unregistered. If there are registered boot consoles when @printk_kthreads_ready is set, no kthreads are created until the final boot console unregisters. Once kthread creation finally occurs, @printk_kthreads_running is set so that the system knows kthreads are available for all registered nbcon consoles. If @printk_kthreads_running is already set when the console is registering, the kthread is created during registration. If kthread creation fails, the registration will fail. Until @printk_kthreads_running is set, console printing occurs directly via the console_lock. kthread shutdown on system shutdown/reboot is necessary to ensure the printer kthreads finish their printing so that the system can cleanly transition back to direct printing via the console_lock in order to reliably push out the final shutdown/reboot messages. @printk_kthreads_running is cleared before shutting down the individual kthreads. The kthread uses a new mandatory write_thread() callback that is called with both device_lock() and the console context acquired. The console ownership handling is necessary for synchronization against write_atomic() which is synchronized only via the console context ownership. The device_lock() serializes acquiring the console context with NBCON_PRIO_NORMAL. It is needed in case the device_lock() does not disable preemption. It prevents the following race: CPU0 CPU1 [ task A ] nbcon_context_try_acquire() # success with NORMAL prio # .unsafe == false; // safe for takeover [ schedule: task A -> B ] WARN_ON() nbcon_atomic_flush_pending() nbcon_context_try_acquire() # success with EMERGENCY prio # flushing nbcon_context_release() # HERE: con->nbcon_state is free # to take by anyone !!! nbcon_context_try_acquire() # success with NORMAL prio [ task B ] [ schedule: task B -> A ] nbcon_enter_unsafe() nbcon_context_can_proceed() BUG: nbcon_context_can_proceed() returns "true" because the console is owned by a context on CPU0 with NBCON_PRIO_NORMAL. But it should return "false". The console is owned by a context from task B and we do the check in a context from task A. Note that with these changes, the printer kthreads do not yet take over full responsibility for nbcon printing during normal operation. These changes only focus on the lifecycle of the kthreads. Co-developed-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-7-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: nbcon: Init @nbcon_seq to highest possibleJohn Ogness
When initializing an nbcon console, have nbcon_alloc() set @nbcon_seq to the highest possible sequence number. For all practical purposes, this will guarantee that the console will have nothing to print until later when @nbcon_seq is set to the proper initial printing value. This will be particularly important once kthread printing is introduced because nbcon_alloc() can create/start the kthread before the desired initial sequence number is known. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-6-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: nbcon: Add context to usable() and emit()John Ogness
The nbcon consoles will have two callbacks to be used for different contexts. In order to determine if an nbcon console is usable, console_is_usable() must know if it is a context that will need to use the optional write_atomic() callback. Also, nbcon_emit_next_record() must know which callback it needs to call. Add an extra parameter @use_atomic to console_is_usable() and nbcon_emit_next_record() to specify this. Since so far only the write_atomic() callback exists, @use_atomic is set to true for all call sites. For legacy consoles, @use_atomic is not used. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-5-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: Flush console on unregister_console()John Ogness
Ensure consoles have flushed pending records before unregistering. The console should print up to at least its related "console disabled" record. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-4-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: Fail pr_flush() if before SYSTEM_SCHEDULINGJohn Ogness
A follow-up change adds pr_flush() to console unregistration. However, with boot consoles unregistration can happen very early if there are also regular consoles registering as well. In this case the pr_flush() is not important because all consoles are flushed when checking the initial console sequence number. Allow pr_flush() to fail if @system_state has not yet reached SYSTEM_SCHEDULING. This avoids might_sleep() and msleep() explosions that would otherwise occur: [ 0.436739][ T0] printk: legacy console [ttyS0] enabled [ 0.439820][ T0] printk: legacy bootconsole [earlyser0] disabled [ 0.446822][ T0] BUG: scheduling while atomic: swapper/0/0/0x00000002 [ 0.450491][ T0] 1 lock held by swapper/0/0: [ 0.457897][ T0] #0: ffffffff82ae5f88 (console_mutex){+.+.}-{4:4}, at: console_list_lock+0x20/0x70 [ 0.463141][ T0] Modules linked in: [ 0.465307][ T0] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.10.0-rc1+ #372 [ 0.469394][ T0] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014 [ 0.474402][ T0] Call Trace: [ 0.476246][ T0] <TASK> [ 0.481473][ T0] dump_stack_lvl+0x93/0xb0 [ 0.483949][ T0] dump_stack+0x10/0x20 [ 0.486256][ T0] __schedule_bug+0x68/0x90 [ 0.488753][ T0] __schedule+0xb9b/0xd80 [ 0.491179][ T0] ? lock_release+0xb5/0x270 [ 0.493732][ T0] schedule+0x43/0x170 [ 0.495998][ T0] schedule_timeout+0xc5/0x1e0 [ 0.498634][ T0] ? __pfx_process_timeout+0x10/0x10 [ 0.501522][ T0] ? msleep+0x13/0x50 [ 0.503728][ T0] msleep+0x3c/0x50 [ 0.505847][ T0] __pr_flush.constprop.0.isra.0+0x56/0x500 [ 0.509050][ T0] ? _printk+0x58/0x80 [ 0.511332][ T0] ? lock_is_held_type+0x9c/0x110 [ 0.514106][ T0] unregister_console_locked+0xe1/0x450 [ 0.517144][ T0] register_console+0x509/0x620 [ 0.519827][ T0] ? __pfx_univ8250_console_init+0x10/0x10 [ 0.523042][ T0] univ8250_console_init+0x24/0x40 [ 0.525845][ T0] console_init+0x43/0x210 [ 0.528280][ T0] start_kernel+0x493/0x980 [ 0.530773][ T0] x86_64_start_reservations+0x18/0x30 [ 0.533755][ T0] x86_64_start_kernel+0xae/0xc0 [ 0.536473][ T0] common_startup_64+0x12c/0x138 [ 0.539210][ T0] </TASK> And then the kernel goes into an infinite loop complaining about: 1. releasing a pinned lock 2. unpinning an unpinned lock 3. bad: scheduling from the idle thread! 4. goto 1 Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-3-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: nbcon: Add function for printers to reacquire ownershipJohn Ogness
Since ownership can be lost at any time due to handover or takeover, a printing context _must_ be prepared to back out immediately and carefully. However, there are scenarios where the printing context must reacquire ownership in order to finalize or revert hardware changes. One such example is when interrupts are disabled during printing. No other context will automagically re-enable the interrupts. For this case, the disabling context _must_ reacquire nbcon ownership so that it can re-enable the interrupts. Provide nbcon_reacquire_nobuf() for exactly this purpose. It allows a printing context to reacquire ownership using the same priority as its previous ownership. Note that after a successful reacquire the printing context will have no output buffer because that has been lost. This function cannot be used to resume printing. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-2-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: nbcon: Use raw_cpu_ptr() instead of open codingJohn Ogness
There is no need to open code a non-migration-checking this_cpu_ptr(). That is exactly what raw_cpu_ptr() is. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/87plpum4jw.fsf@jogness.linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-09-04printk: Use the BITS_PER_LONG macroJinjie Ruan
sizeof(unsigned long) * 8 is the number of bits in an unsigned long variable, replace it with BITS_PER_LONG macro to make it simpler. Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com> Reviewed-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240903035358.308482-1-ruanjinjie@huawei.com Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-27Merge v6.11-rc5 into drm-nextDaniel Vetter
amdgpu pr conconflicts due to patches cherry-picked to -fixes, I might as well catch up with a backmerge and handle them all. Plus both misc and intel maintainers asked for a backmerge anyway. Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
2024-08-21printk: nbcon: Implement emergency sectionsThomas Gleixner
In emergency situations (something has gone wrong but the system continues to operate), usually important information (such as a backtrace) is generated via printk(). This information should be pushed out to the consoles ASAP. Add per-CPU emergency nesting tracking because an emergency can arise while in an emergency situation. Add functions to mark the beginning and end of emergency sections where the urgent messages are generated. Perform direct console flushing at the emergency priority if the current CPU is in an emergency state and it is safe to do so. Note that the emergency state is not system-wide. While one CPU is in an emergency state, another CPU may attempt to print console messages at normal priority. Also note that printk() already attempts to flush consoles in the caller context for normal priority. However, follow-up changes will introduce printing kthreads, in which case the normal priority printk() calls will offload to the kthreads. Co-developed-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-32-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Add helper for flush type logicJohn Ogness
There are many call sites where console flushing occur. Depending on the system state and types of consoles, the flush methods to use are different. A flush call site generally must consider: @have_boot_console @have_nbcon_console @have_legacy_console @legacy_allow_panic_sync is_printk_preferred() and take into account the current CPU state: NBCON_PRIO_NORMAL NBCON_PRIO_EMERGENCY NBCON_PRIO_PANIC in order to decide if it should: flush nbcon directly via atomic_write() callback flush legacy directly via console_unlock flush legacy via offload to irq_work All of these call sites use their own logic to make this decision, which is complicated and error prone. Especially later when two more flush methods will be introduced: flush nbcon via offload to kthread flush legacy via offload to kthread Introduce a new internal struct console_flush_type that specifies which console flushing methods should be used in the context of the caller. Introduce a helper function to fill out console_flush_type to be used for flushing call sites. Replace the logic of all flushing call sites to use the new helper. This change standardizes behavior, leading to both fixes and optimizations across various call sites. For instance, in console_cpu_notify(), the new logic ensures that nbcon consoles are flushed when they aren’t managed by the legacy loop. Similarly, in console_flush_on_panic(), the system no longer needs to flush nbcon consoles if none are present. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-31-john.ogness@linutronix.de [pmladek@suse.com: Updated the commit message.] Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Coordinate direct printing in panicJohn Ogness
If legacy and nbcon consoles are registered and the nbcon consoles are allowed to flush (i.e. no boot consoles registered), the legacy consoles will no longer perform direct printing on the panic CPU until after the backtrace has been stored. This will give the safe nbcon consoles a chance to print the panic messages before allowing the unsafe legacy consoles to print. If no nbcon consoles are registered or they are not allowed to flush because boot consoles are registered, there is no change in behavior (i.e. legacy consoles will always attempt to print from the printk() caller context). Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-30-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Track nbcon consolesJohn Ogness
Add a global flag @have_nbcon_console to identify if any nbcon consoles are registered. This will be used in follow-up commits to preserve legacy behavior when no nbcon consoles are registered. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-29-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Avoid console_lock dance if no legacy or boot consolesJohn Ogness
Currently the console lock is used to attempt legacy-type printing even if there are no legacy or boot consoles registered. If no such consoles are registered, the console lock does not need to be taken. Add tracking of legacy console registration and use it with boot console tracking to avoid unnecessary code paths, i.e. do not use the console lock if there are no boot consoles and no legacy consoles. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-28-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: nbcon: Add unsafe flushing on panicJohn Ogness
Add nbcon_atomic_flush_unsafe() to flush all nbcon consoles using the write_atomic() callback and allowing unsafe hostile takeovers. Call this at the end of panic() as a final attempt to flush any pending messages. Note that legacy consoles use unsafe methods for flushing from the beginning of panic (see bust_spinlocks()). Therefore, systems using both legacy and nbcon consoles may still fail to see panic messages due to unsafe legacy console usage. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-27-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Flush nbcon consoles first on panicJohn Ogness
In console_flush_on_panic(), flush the nbcon consoles before flushing legacy consoles. The legacy write() callbacks are not fully safe when oops_in_progress is set. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-26-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: nbcon: Flush new records on device_release()John Ogness
There may be new records that were added while a driver was holding the nbcon context for non-printing purposes. These new records must be flushed by the nbcon_device_release() context because no other context will do it. If boot consoles are registered, the legacy loop is used (either direct or per irq_work) to handle the flushing. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-25-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Add is_printk_legacy_deferred()John Ogness
If printk has been explicitly deferred or is called from NMI context, legacy console printing must be deferred to an irq_work context. Introduce a helper function is_printk_legacy_deferred() for a CPU to query if it must defer legacy console printing. In follow-up commits this helper will be needed at other call sites as well. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-24-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: nbcon: Use nbcon consoles in console_flush_all()John Ogness
Allow nbcon consoles to print messages in the legacy printk() caller context (printing via unlock) by integrating them into console_flush_all(). The write_atomic() callback is used for printing. Provide nbcon_legacy_emit_next_record(), which acts as the nbcon variant of console_emit_next_record(). Call this variant within console_flush_all() for nbcon consoles. Since nbcon consoles use their own @nbcon_seq variable to track the next record to print, this also must be appropriately handled in console_flush_all(). Note that the legacy printing logic uses @handover to detect handovers for printing all consoles. For nbcon consoles, handovers/takeovers occur on a per-console basis and thus do not cause the console_flush_all() loop to abort. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-23-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Track registered boot consolesJohn Ogness
Unfortunately it is not known if a boot console and a regular (legacy or nbcon) console use the same hardware. For this reason they must not be allowed to print simultaneously. For legacy consoles this is not an issue because they are already synchronized with the boot consoles using the console lock. However nbcon consoles can be triggered separately. Add a global flag @have_boot_console to identify if any boot consoles are registered. This will be used in follow-up commits to ensure that boot consoles and nbcon consoles cannot print simultaneously. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-22-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: nbcon: Provide function to flush using write_atomic()Thomas Gleixner
Provide nbcon_atomic_flush_pending() to perform flushing of all registered nbcon consoles using their write_atomic() callback. Unlike console_flush_all(), nbcon_atomic_flush_pending() will only flush up through the newest record at the time of the call. This prevents a CPU from printing unbounded when other CPUs are adding records. If new records are added while flushing, it is expected that the dedicated printer threads will print those records. If the printer thread is not available (which is always the case at this point in the rework), nbcon_atomic_flush_pending() _will_ flush all records in the ringbuffer. Unlike console_flush_all(), nbcon_atomic_flush_pending() will fully flush one console before flushing the next. This helps to guarantee that a block of pending records (such as a stack trace in an emergency situation) can be printed atomically at once before releasing console ownership. nbcon_atomic_flush_pending() is safe in any context because it uses write_atomic() and acquires with unsafe_takeover disabled. Co-developed-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-21-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: nbcon: Add helper to assign priority based on CPU stateJohn Ogness
Add a helper function to use the current state of the CPU to determine which priority to assign to the printing context. The EMERGENCY priority handling is added in a follow-up commit. It will use a per-CPU variable. Note: nbcon_device_try_acquire(), which is used by console drivers to acquire the nbcon console for non-printing activities, is hard-coded to always use NORMAL priority. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-20-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Add @flags argument for console_is_usable()John Ogness
The caller of console_is_usable() usually needs @console->flags for its own checks. Rather than having console_is_usable() read its own copy, make the caller pass in the @flags. This also ensures that the caller saw the same @flags value. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-19-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Let console_is_usable() handle nbconJohn Ogness
The nbcon consoles use a different printing callback. For nbcon consoles, check for the write_atomic() callback instead of write(). Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-18-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Make console_is_usable() available to nbcon.cJohn Ogness
Move console_is_usable() as-is into internal.h so that it can be used by nbcon printing functions as well. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-17-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: nbcon: Do not rely on proxy headersJohn Ogness
The headers kernel.h, serial_core.h, and console.h allow for the definitions of many types and functions from other headers. Rather than relying on these as proxy headers, explicitly include all headers providing needed definitions. Also sort the list alphabetically to be able to easily detect duplicates. Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Acked-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-16-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21nbcon: Add API to acquire context for non-printing operationsJohn Ogness
Provide functions nbcon_device_try_acquire() and nbcon_device_release() which will try to acquire the nbcon console ownership with NBCON_PRIO_NORMAL and mark it unsafe for handover/takeover. These functions are to be used together with the device-specific locking when performing non-printing activities on the console device. They will allow synchronization against the atomic_write() callback which will be serialized, for higher priority contexts, only by acquiring the console context ownership. Pitfalls: The API requires to be called in a context with migration disabled because it uses per-CPU variables internally. The context is set unsafe for a takeover all the time. It guarantees full serialization against any atomic_write() caller except for the final flush in panic() which might try an unsafe takeover. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-14-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: nbcon: Use driver synchronization while (un)registeringJohn Ogness
Console drivers typically have to deal with access to the hardware via user input/output (such as an interactive login shell) and output of kernel messages via printk() calls. They use some classic driver-specific locking mechanism in most situations. But console->write_atomic() callbacks, used by nbcon consoles, are synchronized only by acquiring the console context. The synchronization via the console context ownership is possible only when the console driver is registered. It is when a particular device driver is connected with a particular console driver. The two synchronization mechanisms must be synchronized between each other. It is tricky because the console context ownership is quite special. It might be taken over by a higher priority context. Also CPU migration must be disabled. The most tricky part is to (dis)connect these two mechanisms during the console (un)registration. Use the driver-specific locking callbacks: device_lock(), device_unlock(). They allow taking the device-specific lock while the device is being (un)registered by the related console driver. For example, these callbacks lock/unlock the port lock for serial port drivers. Note that the driver-specific locking is only needed during (un)register if it is an nbcon console with the write_atomic() callback implemented. If write_atomic() is not implemented, the driver should never attempt to access the hardware without first acquiring its driver-specific lock. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-10-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: nbcon: Remove return value for write_atomic()John Ogness
The return value of write_atomic() does not provide any useful information. On the contrary, it makes things more complicated for the caller to appropriately deal with the information. Change write_atomic() to not have a return value. If the message did not get printed due to loss of ownership, the caller will notice this on its own. If ownership was not lost, it will be assumed that the driver successfully printed the message and the sequence number for that console will be incremented. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-7-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: nbcon: Clarify rules of the owner/waiter matchingJohn Ogness
The functions nbcon_owner_matches() and nbcon_waiter_matches() use a minimal set of data to determine if a context matches. The existing kerneldoc and comments were not clear enough and caused the printk folks to re-prove that the functions are indeed reliable in all cases. Update and expand the explanations so that it is clear that the implementations are sufficient for all cases. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-6-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Check printk_deferred_enter()/_exit() usageSebastian Andrzej Siewior
Add validation that printk_deferred_enter()/_exit() are called in non-migration contexts. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-5-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Properly deal with nbcon consoles on seq initPetr Mladek
If a non-boot console is registering and boot consoles exist, the consoles are flushed before being unregistered. This allows the non-boot console to continue where the boot console left off. If for whatever reason flushing fails, the lowest seq found from any of the enabled boot consoles is used. Until now con->seq was checked. However, if it is an nbcon boot console, the function nbcon_seq_read() must be used to read seq because con->seq is not updated for nbcon consoles. Check if it is an nbcon boot console and if so call nbcon_seq_read() to read seq. Also, avoid usage of con->seq as temporary storage of the starting record. Instead, rename console_init_seq() to get_init_console_seq() and just return the value. For nbcon consoles set the sequence via nbcon_seq_force(), for legacy consoles set con->seq. The cleaned design should make sure that the value stays and is set before the console is added to the console list. It also unifies the sequence number initialization for legacy and nbcon consoles. Reviewed-by: John Ogness <john.ogness@linutronix.de> Link: https://lore.kernel.org/r/20240820063001.36405-4-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: nbcon: Consolidate alloc() and init()John Ogness
Rather than splitting the nbcon allocation and initialization into two pieces, perform all initialization in nbcon_alloc(). Later, the initial sequence is calculated and can be explicitly set using nbcon_seq_force(). This removes the need for the strong rules of nbcon_init() that even included a BUG_ON(). Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240820063001.36405-3-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
2024-08-21printk: Add notation to console_srcu lockingJohn Ogness
kernel/printk/printk.c:284:5: sparse: sparse: context imbalance in 'console_srcu_read_lock' - wrong count at exit include/linux/srcu.h:301:9: sparse: sparse: context imbalance in 'console_srcu_read_unlock' - unexpected unlock Fixes: 6c4afa79147e ("printk: Prepare for SRCU console list protection") Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Acked-by: Paul E. McKenney <paulmck@kernel.org> Link: https://lore.kernel.org/r/20240820063001.36405-2-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
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