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  1. 09 Feb, 2016 3 commits
    • Tejun Heo's avatar
      workqueue: implement "workqueue.debug_force_rr_cpu" debug feature · f303fccb
      Tejun Heo authored 
      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 041bd12e
("Revert "workqueue: make sure delayed work run in local cpu"") for
more information and ping me.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      f303fccb
    • Mike Galbraith's avatar
      workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs · ef557180
      Mike Galbraith authored 
      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: default avatarMike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      ef557180
    • Tejun Heo's avatar
      Revert "workqueue: make sure delayed work run in local cpu" · 041bd12e
      Tejun Heo authored 
      This reverts commit 874bbfe6.

Workqueue used to implicity guarantee that work items queued without
explicit CPU specified are put on the local CPU.  Recent changes in
timer broke the guarantee and led to vmstat breakage which was fixed
by 176bed1d ("vmstat: explicitly schedule per-cpu work on the CPU
we need it to run on").

vmstat is the most likely to expose the issue and it's quite possible
that there are other similar problems which are a lot more difficult
to trigger.  As a preventive measure, 874bbfe6 ("workqueue: make
sure delayed work run in local cpu") was applied to restore the local
CPU guarnatee.  Unfortunately, the change exposed a bug in timer code
which got fixed by 22b886dd ("timers: Use proper base migration in
add_timer_on()").  Due to code restructuring, the commit couldn't be
backported beyond certain point and stable kernels which only had
874bbfe6 started crashing.

The local CPU guarantee was accidental more than anything else and we
want to get rid of it anyway.  As, with the vmstat case fixed,
874bbfe6 is causing more problems than it's fixing, it has been
decided to take the chance and officially break the guarantee by
reverting the commit.  A debug feature will be added to force foreign
CPU assignment to expose cases relying on the guarantee and fixes for
the individual cases will be backported to stable as necessary.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Fixes: 874bbfe6 ("workqueue: make sure delayed work run in local cpu")
Link: http://lkml.kernel.org/g/20160120211926.GJ10810@quack.suse.cz
Cc: stable@vger.kernel.org
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Daniel Bilik <daniel.bilik@neosystem.cz>
Cc: Jan Kara <jack@suse.cz>
Cc: Shaohua Li <shli@fb.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Daniel Bilik <daniel.bilik@neosystem.cz>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>
      041bd12e
  3. 29 Jan, 2016 1 commit
    • Tejun Heo's avatar
      workqueue: skip flush dependency checks for legacy workqueues · 23d11a58
      Tejun Heo authored 
      fca839c0 ("workqueue: warn if memory reclaim tries to flush
!WQ_MEM_RECLAIM workqueue") implemented flush dependency warning which
triggers if a PF_MEMALLOC task or WQ_MEM_RECLAIM workqueue tries to
flush a !WQ_MEM_RECLAIM workquee.

This assumes that workqueues marked with WQ_MEM_RECLAIM sit in memory
reclaim path and making it depend on something which may need more
memory to make forward progress can lead to deadlocks.  Unfortunately,
workqueues created with the legacy create*_workqueue() interface
always have WQ_MEM_RECLAIM regardless of whether they are depended
upon memory reclaim or not.  These spurious WQ_MEM_RECLAIM markings
cause spurious triggering of the flush dependency checks.

  WARNING: CPU: 0 PID: 6 at kernel/workqueue.c:2361 check_flush_dependency+0x138/0x144()
  workqueue: WQ_MEM_RECLAIM deferwq:deferred_probe_work_func is flushing !WQ_MEM_RECLAIM events:lru_add_drain_per_cpu
  ...
  Workqueue: deferwq deferred_probe_work_func
  [<c0017acc>] (unwind_backtrace) from [<c0013134>] (show_stack+0x10/0x14)
  [<c0013134>] (show_stack) from [<c0245f18>] (dump_stack+0x94/0xd4)
  [<c0245f18>] (dump_stack) from [<c0026f9c>] (warn_slowpath_common+0x80/0xb0)
  [<c0026f9c>] (warn_slowpath_common) from [<c0026ffc>] (warn_slowpath_fmt+0x30/0x40)
  [<c0026ffc>] (warn_slowpath_fmt) from [<c00390b8>] (check_flush_dependency+0x138/0x144)
  [<c00390b8>] (check_flush_dependency) from [<c0039ca0>] (flush_work+0x50/0x15c)
  [<c0039ca0>] (flush_work) from [<c00c51b0>] (lru_add_drain_all+0x130/0x180)
  [<c00c51b0>] (lru_add_drain_all) from [<c00f728c>] (migrate_prep+0x8/0x10)
  [<c00f728c>] (migrate_prep) from [<c00bfbc4>] (alloc_contig_range+0xd8/0x338)
  [<c00bfbc4>] (alloc_contig_range) from [<c00f8f18>] (cma_alloc+0xe0/0x1ac)
  [<c00f8f18>] (cma_alloc) from [<c001cac4>] (__alloc_from_contiguous+0x38/0xd8)
  [<c001cac4>] (__alloc_from_contiguous) from [<c001ceb4>] (__dma_alloc+0x240/0x278)
  [<c001ceb4>] (__dma_alloc) from [<c001cf78>] (arm_dma_alloc+0x54/0x5c)
  [<c001cf78>] (arm_dma_alloc) from [<c0355ea4>] (dmam_alloc_coherent+0xc0/0xec)
  [<c0355ea4>] (dmam_alloc_coherent) from [<c039cc4c>] (ahci_port_start+0x150/0x1dc)
  [<c039cc4c>] (ahci_port_start) from [<c0384734>] (ata_host_start.part.3+0xc8/0x1c8)
  [<c0384734>] (ata_host_start.part.3) from [<c03898dc>] (ata_host_activate+0x50/0x148)
  [<c03898dc>] (ata_host_activate) from [<c039d558>] (ahci_host_activate+0x44/0x114)
  [<c039d558>] (ahci_host_activate) from [<c039f05c>] (ahci_platform_init_host+0x1d8/0x3c8)
  [<c039f05c>] (ahci_platform_init_host) from [<c039e6bc>] (tegra_ahci_probe+0x448/0x4e8)
  [<c039e6bc>] (tegra_ahci_probe) from [<c0347058>] (platform_drv_probe+0x50/0xac)
  [<c0347058>] (platform_drv_probe) from [<c03458cc>] (driver_probe_device+0x214/0x2c0)
  [<c03458cc>] (driver_probe_device) from [<c0343cc0>] (bus_for_each_drv+0x60/0x94)
  [<c0343cc0>] (bus_for_each_drv) from [<c03455d8>] (__device_attach+0xb0/0x114)
  [<c03455d8>] (__device_attach) from [<c0344ab8>] (bus_probe_device+0x84/0x8c)
  [<c0344ab8>] (bus_probe_device) from [<c0344f48>] (deferred_probe_work_func+0x68/0x98)
  [<c0344f48>] (deferred_probe_work_func) from [<c003b738>] (process_one_work+0x120/0x3f8)
  [<c003b738>] (process_one_work) from [<c003ba48>] (worker_thread+0x38/0x55c)
  [<c003ba48>] (worker_thread) from [<c0040f14>] (kthread+0xdc/0xf4)
  [<c0040f14>] (kthread) from [<c000f778>] (ret_from_fork+0x14/0x3c)

Fix it by marking workqueues created via create*_workqueue() with
__WQ_LEGACY and disabling flush dependency checks on them.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reported-and-tested-by: default avatarThierry Reding <thierry.reding@gmail.com>
Link: http://lkml.kernel.org/g/20160126173843.GA11115@ulmo.nvidia.com
Fixes: fca839c0 ("workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue")
      23d11a58
  5. 24 Jan, 2016 36 commits
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