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    Subject[PATCH AUTOSEL 4.19 31/60] uio: free uio id after uio file node is freed
    Date
    From: Lang Dai <lang.dai@intel.com>

    [ Upstream commit 8fd0e2a6df262539eaa28b0a2364cca10d1dc662 ]

    uio_register_device() do two things.
    1) get an uio id from a global pool, e.g. the id is <A>
    2) create file nodes like /sys/class/uio/uio<A>

    uio_unregister_device() do two things.
    1) free the uio id <A> and return it to the global pool
    2) free the file node /sys/class/uio/uio<A>

    There is a situation is that one worker is calling uio_unregister_device(),
    and another worker is calling uio_register_device().
    If the two workers are X and Y, they go as below sequence,
    1) X free the uio id <AAA>
    2) Y get an uio id <AAA>
    3) Y create file node /sys/class/uio/uio<AAA>
    4) X free the file note /sys/class/uio/uio<AAA>
    Then it will failed at the 3rd step and cause the phenomenon we saw as it
    is creating a duplicated file node.

    Failure reports as follows:
    sysfs: cannot create duplicate filename '/class/uio/uio10'
    Call Trace:
    sysfs_do_create_link_sd.isra.2+0x9e/0xb0
    sysfs_create_link+0x25/0x40
    device_add+0x2c4/0x640
    __uio_register_device+0x1c5/0x576 [uio]
    adf_uio_init_bundle_dev+0x231/0x280 [intel_qat]
    adf_uio_register+0x1c0/0x340 [intel_qat]
    adf_dev_start+0x202/0x370 [intel_qat]
    adf_dev_start_async+0x40/0xa0 [intel_qat]
    process_one_work+0x14d/0x410
    worker_thread+0x4b/0x460
    kthread+0x105/0x140
    ? process_one_work+0x410/0x410
    ? kthread_bind+0x40/0x40
    ret_from_fork+0x1f/0x40
    Code: 85 c0 48 89 c3 74 12 b9 00 10 00 00 48 89 c2 31 f6 4c 89 ef
    e8 ec c4 ff ff 4c 89 e2 48 89 de 48 c7 c7 e8 b4 ee b4 e8 6a d4 d7
    ff <0f> 0b 48 89 df e8 20 fa f3 ff 5b 41 5c 41 5d 5d c3 66 0f 1f 84
    ---[ end trace a7531c1ed5269e84 ]---
    c6xxvf b002:00:00.0: Failed to register UIO devices
    c6xxvf b002:00:00.0: Failed to register UIO devices

    Signed-off-by: Lang Dai <lang.dai@intel.com>

    Link: https://lore.kernel.org/r/1600054002-17722-1-git-send-email-lang.dai@intel.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/uio/uio.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
    index 9c788748bdc65..3926be6591471 100644
    --- a/drivers/uio/uio.c
    +++ b/drivers/uio/uio.c
    @@ -1008,8 +1008,6 @@ void uio_unregister_device(struct uio_info *info)

    idev = info->uio_dev;

    - uio_free_minor(idev);
    -
    mutex_lock(&idev->info_lock);
    uio_dev_del_attributes(idev);

    @@ -1021,6 +1019,8 @@ void uio_unregister_device(struct uio_info *info)

    device_unregister(&idev->dev);

    + uio_free_minor(idev);
    +
    return;
    }
    EXPORT_SYMBOL_GPL(uio_unregister_device);
    --
    2.25.1
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