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    Subject[PATCH wq/for-4.5-fixes] workqueue: skip flush dependency checks for legacy workqueues
    fca839c00a12 ("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: Tejun Heo <tj@kernel.org>
    Reported-by: Thierry Reding <thierry.reding@gmail.com>
    Link: http://lkml.kernel.org/g/20160126173843.GA11115@ulmo.nvidia.com
    ---
    Hello, Thierry.

    Can youp please verify the fix?

    Thanks.

    include/linux/workqueue.h | 9 +++++----
    kernel/workqueue.c | 3 ++-
    2 files changed, 7 insertions(+), 5 deletions(-)

    diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
    index 0e32bc7..ca73c50 100644
    --- a/include/linux/workqueue.h
    +++ b/include/linux/workqueue.h
    @@ -311,6 +311,7 @@ enum {

    __WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */
    __WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */
    + __WQ_LEGACY = 1 << 18, /* internal: create*_workqueue() */

    WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
    WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */
    @@ -411,12 +412,12 @@ __alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,
    alloc_workqueue(fmt, WQ_UNBOUND | __WQ_ORDERED | (flags), 1, ##args)

    #define create_workqueue(name) \
    - alloc_workqueue("%s", WQ_MEM_RECLAIM, 1, (name))
    + alloc_workqueue("%s", __WQ_LEGACY | WQ_MEM_RECLAIM, 1, (name))
    #define create_freezable_workqueue(name) \
    - alloc_workqueue("%s", WQ_FREEZABLE | WQ_UNBOUND | WQ_MEM_RECLAIM, \
    - 1, (name))
    + alloc_workqueue("%s", __WQ_LEGACY | WQ_FREEZABLE | WQ_UNBOUND | \
    + WQ_MEM_RECLAIM, 1, (name))
    #define create_singlethread_workqueue(name) \
    - alloc_ordered_workqueue("%s", WQ_MEM_RECLAIM, name)
    + alloc_ordered_workqueue("%s", __WQ_LEGACY | WQ_MEM_RECLAIM, name)

    extern void destroy_workqueue(struct workqueue_struct *wq);

    diff --git a/kernel/workqueue.c b/kernel/workqueue.c
    index 61a0264..dc7faad 100644
    --- a/kernel/workqueue.c
    +++ b/kernel/workqueue.c
    @@ -2355,7 +2355,8 @@ static void check_flush_dependency(struct workqueue_struct *target_wq,
    WARN_ONCE(current->flags & PF_MEMALLOC,
    "workqueue: PF_MEMALLOC task %d(%s) is flushing !WQ_MEM_RECLAIM %s:%pf",
    current->pid, current->comm, target_wq->name, target_func);
    - WARN_ONCE(worker && (worker->current_pwq->wq->flags & WQ_MEM_RECLAIM),
    + WARN_ONCE(worker && ((worker->current_pwq->wq->flags &
    + (WQ_MEM_RECLAIM | __WQ_LEGACY)) == WQ_MEM_RECLAIM),
    "workqueue: WQ_MEM_RECLAIM %s:%pf is flushing !WQ_MEM_RECLAIM %s:%pf",
    worker->current_pwq->wq->name, worker->current_func,
    target_wq->name, target_func);
    \
     
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      Last update: 2016-01-29 12:21    [W:4.410 / U:0.548 seconds]
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