Merge tag 'rcu.2023.02.10a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU updates from Paul McKenney:

 - Documentation updates

 - Miscellaneous fixes, perhaps most notably:

      - Throttling callback invocation based on the number of callbacks
        that are now ready to invoke instead of on the total number of
        callbacks

      - Several patches that suppress false-positive boot-time
        diagnostics, for example, due to lockdep not yet being
        initialized

      - Make expedited RCU CPU stall warnings dump stacks of any tasks
        that are blocking the stalled grace period. (Normal RCU CPU
        stall warnings have done this for many years)

      - Lazy-callback fixes to avoid delays during boot, suspend, and
        resume. (Note that lazy callbacks must be explicitly enabled, so
        this should not (yet) affect production use cases)

 - Make kfree_rcu() and friends take advantage of polled grace periods,
   thus reducing memory footprint by almost two orders of magnitude,
   admittedly on a microbenchmark

   This also begins the transition from kfree_rcu(p) to
   kfree_rcu_mightsleep(p). This transition was motivated by bugs where
   kfree_rcu(p), which can block, was typed instead of the intended
   kfree_rcu(p, rh)

 - SRCU updates, perhaps most notably fixing a bug that causes SRCU to
   fail when booted on a system with a non-zero boot CPU. This
   surprising situation actually happens for kdump kernels on the
   powerpc architecture

   This also adds an srcu_down_read() and srcu_up_read(), which act like
   srcu_read_lock() and srcu_read_unlock(), but allow an SRCU read-side
   critical section to be handed off from one task to another

 - Clean up the now-useless SRCU Kconfig option

   There are a few more commits that are not yet acked or pulled into
   maintainer trees, and these will be in a pull request for a later
   merge window

 - RCU-tasks updates, perhaps most notably these fixes:

      - A strange interaction between PID-namespace unshare and the
        RCU-tasks grace period that results in a low-probability but
        very real hang

      - A race between an RCU tasks rude grace period on a single-CPU
        system and CPU-hotplug addition of the second CPU that can
        result in a too-short grace period

      - A race between shrinking RCU tasks down to a single callback
        list and queuing a new callback to some other CPU, but where
        that queuing is delayed for more than an RCU grace period. This
        can result in that callback being stranded on the non-boot CPU

 - Torture-test updates and fixes

 - Torture-test scripting updates and fixes

 - Provide additional RCU CPU stall-warning information in kernels built
   with CONFIG_RCU_CPU_STALL_CPUTIME=y, and restore the full five-minute
   timeout limit for expedited RCU CPU stall warnings

* tag 'rcu.2023.02.10a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (80 commits)
  rcu/kvfree: Add kvfree_rcu_mightsleep() and kfree_rcu_mightsleep()
  kernel/notifier: Remove CONFIG_SRCU
  init: Remove "select SRCU"
  fs/quota: Remove "select SRCU"
  fs/notify: Remove "select SRCU"
  fs/btrfs: Remove "select SRCU"
  fs: Remove CONFIG_SRCU
  drivers/pci/controller: Remove "select SRCU"
  drivers/net: Remove "select SRCU"
  drivers/md: Remove "select SRCU"
  drivers/hwtracing/stm: Remove "select SRCU"
  drivers/dax: Remove "select SRCU"
  drivers/base: Remove CONFIG_SRCU
  rcu: Disable laziness if lazy-tracking says so
  rcu: Track laziness during boot and suspend
  rcu: Remove redundant call to rcu_boost_kthread_setaffinity()
  rcu: Allow up to five minutes expedited RCU CPU stall-warning timeouts
  rcu: Align the output of RCU CPU stall warning messages
  rcu: Add RCU stall diagnosis information
  sched: Add helper nr_context_switches_cpu()
  ...

6 files changed, 1 insertions, 47 deletions

diff --git a/drivers/base/core.c b/drivers/base/core.c
index a3e14143ec0c..bb36aca8d1b7 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -181,7 +181,6 @@ void fw_devlink_purge_absent_suppliers(struct fwnode_handle *fwnode)
 }
 EXPORT_SYMBOL_GPL(fw_devlink_purge_absent_suppliers);
 
-#ifdef CONFIG_SRCU
 static DEFINE_MUTEX(device_links_lock);
 DEFINE_STATIC_SRCU(device_links_srcu);
 
@@ -220,47 +219,6 @@ static void device_link_remove_from_lists(struct device_link *link)
 	list_del_rcu(&link->s_node);
 	list_del_rcu(&link->c_node);
 }
-#else /* !CONFIG_SRCU */
-static DECLARE_RWSEM(device_links_lock);
-
-static inline void device_links_write_lock(void)
-{
-	down_write(&device_links_lock);
-}
-
-static inline void device_links_write_unlock(void)
-{
-	up_write(&device_links_lock);
-}
-
-int device_links_read_lock(void)
-{
-	down_read(&device_links_lock);
-	return 0;
-}
-
-void device_links_read_unlock(int not_used)
-{
-	up_read(&device_links_lock);
-}
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-int device_links_read_lock_held(void)
-{
-	return lockdep_is_held(&device_links_lock);
-}
-#endif
-
-static inline void device_link_synchronize_removal(void)
-{
-}
-
-static void device_link_remove_from_lists(struct device_link *link)
-{
-	list_del(&link->s_node);
-	list_del(&link->c_node);
-}
-#endif /* !CONFIG_SRCU */
 
 static bool device_is_ancestor(struct device *dev, struct device *target)
 {
diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index 5fdf269a822e..2bf5123e4827 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig
@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 menuconfig DAX
 	tristate "DAX: direct access to differentiated memory"
-	select SRCU
 	default m if NVDIMM_DAX
 
 if DAX
diff --git a/drivers/hwtracing/stm/Kconfig b/drivers/hwtracing/stm/Kconfig
index aad594fe79cc..eda6b11d40a1 100644
--- a/drivers/hwtracing/stm/Kconfig
+++ b/drivers/hwtracing/stm/Kconfig
@@ -2,7 +2,6 @@
 config STM
 	tristate "System Trace Module devices"
 	select CONFIGFS_FS
-	select SRCU
 	help
 	  A System Trace Module (STM) is a device exporting data in System
 	  Trace Protocol (STP) format as defined by MIPI STP standards.
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 998a5cfdbc4e..5f1e2593fad7 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -6,7 +6,6 @@
 menuconfig MD
 	bool "Multiple devices driver support (RAID and LVM)"
 	depends on BLOCK
-	select SRCU
 	help
 	  Support multiple physical spindles through a single logical device.
 	  Required for RAID and logical volume management.
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 9e63b8c43f3e..12910338ea1a 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -334,7 +334,6 @@ config NETCONSOLE_DYNAMIC
 
 config NETPOLL
 	def_bool NETCONSOLE
-	select SRCU
 
 config NET_POLL_CONTROLLER
 	def_bool NETPOLL
diff --git a/drivers/pci/controller/Kconfig b/drivers/pci/controller/Kconfig
index 1569d9a3ada0..b09cdc59bfd0 100644
--- a/drivers/pci/controller/Kconfig
+++ b/drivers/pci/controller/Kconfig
@@ -258,7 +258,7 @@ config PCIE_MEDIATEK_GEN3
 	  MediaTek SoCs.
 
 config VMD
-	depends on PCI_MSI && X86_64 && SRCU && !UML
+	depends on PCI_MSI && X86_64 && !UML
 	tristate "Intel Volume Management Device Driver"
 	help
 	  Adds support for the Intel Volume Management Device (VMD). VMD is a