lkml.org 
[lkml]   [2020]   [Nov]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.19 163/191] ubi: check kthread_should_stop() after the setting of task state
    Date
    From: Zhihao Cheng <chengzhihao1@huawei.com>

    commit d005f8c6588efcfbe88099b6edafc6f58c84a9c1 upstream.

    A detach hung is possible when a race occurs between the detach process
    and the ubi background thread. The following sequences outline the race:

    ubi thread: if (list_empty(&ubi->works)...

    ubi detach: set_bit(KTHREAD_SHOULD_STOP, &kthread->flags)
    => by kthread_stop()
    wake_up_process()
    => ubi thread is still running, so 0 is returned

    ubi thread: set_current_state(TASK_INTERRUPTIBLE)
    schedule()
    => ubi thread will never be scheduled again

    ubi detach: wait_for_completion()
    => hung task!

    To fix that, we need to check kthread_should_stop() after we set the
    task state, so the ubi thread will either see the stop bit and exit or
    the task state is reset to runnable such that it isn't scheduled out
    indefinitely.

    Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
    Cc: <stable@vger.kernel.org>
    Fixes: 801c135ce73d5df1ca ("UBI: Unsorted Block Images")
    Reported-by: syzbot+853639d0cb16c31c7a14@syzkaller.appspotmail.com
    Signed-off-by: Richard Weinberger <richard@nod.at>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/mtd/ubi/wl.c | 13 +++++++++++++
    1 file changed, 13 insertions(+)

    --- a/drivers/mtd/ubi/wl.c
    +++ b/drivers/mtd/ubi/wl.c
    @@ -1471,6 +1471,19 @@ int ubi_thread(void *u)
    !ubi->thread_enabled || ubi_dbg_is_bgt_disabled(ubi)) {
    set_current_state(TASK_INTERRUPTIBLE);
    spin_unlock(&ubi->wl_lock);
    +
    + /*
    + * Check kthread_should_stop() after we set the task
    + * state to guarantee that we either see the stop bit
    + * and exit or the task state is reset to runnable such
    + * that it's not scheduled out indefinitely and detects
    + * the stop bit at kthread_should_stop().
    + */
    + if (kthread_should_stop()) {
    + set_current_state(TASK_RUNNING);
    + break;
    + }
    +
    schedule();
    continue;
    }

    \
     
     \ /
      Last update: 2020-11-03 22:07    [W:4.075 / U:0.296 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site