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    Subject[PATCH 3/5] blktrace: refcount the request_queue during ioctl
    Date
    Ensure that the request_queue is refcounted during its full
    ioctl cycle. This avoids possible races against removal, given
    blk_get_queue() also checks to ensure the queue is not dying.

    This small race is possible if you defer removal of the request_queue
    and userspace fires off an ioctl for the device in the meantime.

    Cc: Bart Van Assche <bvanassche@acm.org>
    Cc: Omar Sandoval <osandov@fb.com>
    Cc: Hannes Reinecke <hare@suse.com>
    Cc: Nicolai Stange <nstange@suse.de>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: yu kuai <yukuai3@huawei.com>
    Reviewed-by: Bart Van Assche <bvanassche@acm.org>
    Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
    ---
    kernel/trace/blktrace.c | 6 ++++++
    1 file changed, 6 insertions(+)

    diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
    index 15086227592f..17e144d15779 100644
    --- a/kernel/trace/blktrace.c
    +++ b/kernel/trace/blktrace.c
    @@ -701,6 +701,9 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
    if (!q)
    return -ENXIO;

    + if (!blk_get_queue(q))
    + return -ENXIO;
    +
    mutex_lock(&q->blk_trace_mutex);

    switch (cmd) {
    @@ -729,6 +732,9 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
    }

    mutex_unlock(&q->blk_trace_mutex);
    +
    + blk_put_queue(q);
    +
    return ret;
    }

    --
    2.25.1
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