pm24.git/kernel/workqueue.c, branch v4.6-rc7

Merge branch 'for-4.6-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq

2016-04-27T19:03:59Z

Pull workqueue fix from Tejun Heo: "So, it turns out we had a silly bug in the most fundamental part of workqueue for a very long time. AFAICS, this dates back to pre-git era and has quite likely been there from the time workqueue was first introduced. A work item uses its PENDING bit to synchronize multiple queuers. Anyone who wins the PENDING bit owns the pending state of the work item. Whether a queuer wins or loses the race, one thing should be guaranteed - there will soon be at least one execution of the work item - where "after" means that the execution instance would be able to see all the changes that the queuer has made prior to the queueing attempt. Unfortunately, we were missing a smp_mb() after clearing PENDING for execution, so nothing guaranteed visibility of the changes that a queueing loser has made, which manifested as a reproducible blk-mq stall. Lots of kudos to Roman for debugging the problem. The patch for -stable is the minimal one. For v3.7, Peter is working on a patch to make the code path slightly more efficient and less fragile" * 'for-4.6-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq: workqueue: fix ghost PENDING flag while doing MQ IO

workqueue: fix ghost PENDING flag while doing MQ IO

2016-04-26T15:23:22Z

The bug in a workqueue leads to a stalled IO request in MQ ctx->rq_list with the following backtrace: [ 601.347452] INFO: task kworker/u129:5:1636 blocked for more than 120 seconds. [ 601.347574] Tainted: G O 4.4.5-1-storage+ #6 [ 601.347651] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 601.348142] kworker/u129:5 D ffff880803077988 0 1636 2 0x00000000 [ 601.348519] Workqueue: ibnbd_server_fileio_wq ibnbd_dev_file_submit_io_worker [ibnbd_server] [ 601.348999] ffff880803077988 ffff88080466b900 ffff8808033f9c80 ffff880803078000 [ 601.349662] ffff880807c95000 7fffffffffffffff ffffffff815b0920 ffff880803077ad0 [ 601.350333] ffff8808030779a0 ffffffff815b01d5 0000000000000000 ffff880803077a38 [ 601.350965] Call Trace: [ 601.351203] [] ? bit_wait+0x60/0x60 [ 601.351444] [] schedule+0x35/0x80 [ 601.351709] [] schedule_timeout+0x192/0x230 [ 601.351958] [] ? blk_flush_plug_list+0xc7/0x220 [ 601.352208] [] ? ktime_get+0x37/0xa0 [ 601.352446] [] ? bit_wait+0x60/0x60 [ 601.352688] [] io_schedule_timeout+0xa4/0x110 [ 601.352951] [] ? _raw_spin_unlock_irqrestore+0xe/0x10 [ 601.353196] [] bit_wait_io+0x1b/0x70 [ 601.353440] [] __wait_on_bit+0x5d/0x90 [ 601.353689] [] wait_on_page_bit+0xc0/0xd0 [ 601.353958] [] ? autoremove_wake_function+0x40/0x40 [ 601.354200] [] __filemap_fdatawait_range+0xe4/0x140 [ 601.354441] [] filemap_fdatawait_range+0x14/0x30 [ 601.354688] [] filemap_write_and_wait_range+0x3f/0x70 [ 601.354932] [] blkdev_fsync+0x1b/0x50 [ 601.355193] [] vfs_fsync_range+0x49/0xa0 [ 601.355432] [] blkdev_write_iter+0xca/0x100 [ 601.355679] [] __vfs_write+0xaa/0xe0 [ 601.355925] [] vfs_write+0xa9/0x1a0 [ 601.356164] [] kernel_write+0x38/0x50 The underlying device is a null_blk, with default parameters: queue_mode = MQ submit_queues = 1 Verification that nullb0 has something inflight: root@pserver8:~# cat /sys/block/nullb0/inflight 0 1 root@pserver8:~# find /sys/block/nullb0/mq/0/cpu* -name rq_list -print -exec cat {} \; ... /sys/block/nullb0/mq/0/cpu2/rq_list CTX pending: ffff8838038e2400 ... During debug it became clear that stalled request is always inserted in the rq_list from the following path: save_stack_trace_tsk + 34 blk_mq_insert_requests + 231 blk_mq_flush_plug_list + 281 blk_flush_plug_list + 199 wait_on_page_bit + 192 __filemap_fdatawait_range + 228 filemap_fdatawait_range + 20 filemap_write_and_wait_range + 63 blkdev_fsync + 27 vfs_fsync_range + 73 blkdev_write_iter + 202 __vfs_write + 170 vfs_write + 169 kernel_write + 56 So blk_flush_plug_list() was called with from_schedule == true. If from_schedule is true, that means that finally blk_mq_insert_requests() offloads execution of __blk_mq_run_hw_queue() and uses kblockd workqueue, i.e. it calls kblockd_schedule_delayed_work_on(). That means, that we race with another CPU, which is about to execute __blk_mq_run_hw_queue() work. Further debugging shows the following traces from different CPUs: CPU#0 CPU#1 ---------------------------------- ------------------------------- reqeust A inserted STORE hctx->ctx_map[0] bit marked kblockd_schedule...() returns 1 request B inserted STORE hctx->ctx_map[1] bit marked kblockd_schedule...() returns 0 *** WORK PENDING bit is cleared *** flush_busy_ctxs() is executed, but bit 1, set by CPU#1, is not observed As a result request B pended forever. This behaviour can be explained by speculative LOAD of hctx->ctx_map on CPU#0, which is reordered with clear of PENDING bit and executed _before_ actual STORE of bit 1 on CPU#1. The proper fix is an explicit full barrier , which guarantees that clear of PENDING bit is to be executed before all possible speculative LOADS or STORES inside actual work function. Signed-off-by: Roman Pen Cc: Gioh Kim Cc: Michael Wang Cc: Tejun Heo Cc: Jens Axboe Cc: linux-block@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Tejun Heo

Merge branch 'for-4.6' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq

2016-03-19T03:05:39Z

Pull workqueue updates from Tejun Heo: "Three trivial workqueue changes" * 'for-4.6' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq: workqueue: Fix comment for work_on_cpu() sched/core: Get rid of 'cpu' argument in wq_worker_sleeping() workqueue: Replace usage of init_name with dev_set_name()

tags: Fix DEFINE_PER_CPU expansions

2016-03-15T23:55:16Z

$ make tags GEN tags ctags: Warning: drivers/acpi/processor_idle.c:64: null expansion of name pattern "\1" ctags: Warning: drivers/xen/events/events_2l.c:41: null expansion of name pattern "\1" ctags: Warning: kernel/locking/lockdep.c:151: null expansion of name pattern "\1" ctags: Warning: kernel/rcu/rcutorture.c:133: null expansion of name pattern "\1" ctags: Warning: kernel/rcu/rcutorture.c:135: null expansion of name pattern "\1" ctags: Warning: kernel/workqueue.c:323: null expansion of name pattern "\1" ctags: Warning: net/ipv4/syncookies.c:53: null expansion of name pattern "\1" ctags: Warning: net/ipv6/syncookies.c:44: null expansion of name pattern "\1" ctags: Warning: net/rds/page.c:45: null expansion of name pattern "\1" Which are all the result of the DEFINE_PER_CPU pattern: scripts/tags.sh:200: '/\ Acked-by: David S. Miller Acked-by: Rafael J. Wysocki Cc: Tejun Heo Cc: "Paul E. McKenney" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

workqueue: Fix comment for work_on_cpu()

2016-03-11T17:39:01Z

Function is processed in thread context, not in user context. Cc: Tejun Heo Cc: Lai Jiangshan Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Anna-Maria Gleixner Signed-off-by: Tejun Heo

sched/core: Get rid of 'cpu' argument in wq_worker_sleeping()

2016-03-02T15:28:47Z

Given that wq_worker_sleeping() could only be called for a CPU it is running on, we do not need passing a CPU ID as an argument. Suggested-by: Oleg Nesterov Cc: Oleg Nesterov Cc: Peter Zijlstra Signed-off-by: Alexander Gordeev Signed-off-by: Tejun Heo

workqueue: Replace usage of init_name with dev_set_name()

2016-02-17T21:14:18Z

The init_name property of the device struct is sort of a hack and should only be used for statically allocated devices. Since the device is dynamically allocated here it is safe to use the proper way to set a devices name by calling dev_set_name(). Signed-off-by: Lars-Peter Clausen Signed-off-by: Tejun Heo

workqueue: handle NUMA_NO_NODE for unbound pool_workqueue lookup

2016-02-10T17:13:05Z

When looking up the pool_workqueue to use for an unbound workqueue, workqueue assumes that the target CPU is always bound to a valid NUMA node. However, currently, when a CPU goes offline, the mapping is destroyed and cpu_to_node() returns NUMA_NO_NODE. This has always been broken but hasn't triggered often enough before 874bbfe600a6 ("workqueue: make sure delayed work run in local cpu"). After the commit, workqueue forcifully assigns the local CPU for delayed work items without explicit target CPU to fix a different issue. This widens the window where CPU can go offline while a delayed work item is pending causing delayed work items dispatched with target CPU set to an already offlined CPU. The resulting NUMA_NO_NODE mapping makes workqueue try to queue the work item on a NULL pool_workqueue and thus crash. While 874bbfe600a6 has been reverted for a different reason making the bug less visible again, it can still happen. Fix it by mapping NUMA_NO_NODE to the default pool_workqueue from unbound_pwq_by_node(). This is a temporary workaround. The long term solution is keeping CPU -> NODE mapping stable across CPU off/online cycles which is being worked on. Signed-off-by: Tejun Heo Reported-by: Mike Galbraith Cc: Tang Chen Cc: Rafael J. Wysocki Cc: Len Brown Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/g/1454424264.11183.46.camel@gmail.com Link: http://lkml.kernel.org/g/1453702100-2597-1-git-send-email-tangchen@cn.fujitsu.com

workqueue: implement "workqueue.debug_force_rr_cpu" debug feature

2016-02-09T22:59:38Z

Workqueue used to guarantee local execution for work items queued without explicit target CPU. The guarantee is gone now which can break some usages in subtle ways. To flush out those cases, this patch implements a debug feature which forces round-robin CPU selection for all such work items. The debug feature defaults to off and can be enabled with a kernel parameter. The default can be flipped with a debug config option. If you hit this commit during bisection, please refer to 041bd12e272c ("Revert "workqueue: make sure delayed work run in local cpu"") for more information and ping me. Signed-off-by: Tejun Heo

workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs

2016-02-09T22:59:38Z

WORK_CPU_UNBOUND work items queued to a bound workqueue always run locally. This is a good thing normally, but not when the user has asked us to keep unbound work away from certain CPUs. Round robin these to wq_unbound_cpumask CPUs instead, as perturbation avoidance trumps performance. tj: Cosmetic and comment changes. WARN_ON_ONCE() dropped from empty (wq_unbound_cpumask AND cpu_online_mask). If we want that, it should be done when config changes. Signed-off-by: Mike Galbraith Signed-off-by: Tejun Heo