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 @@ -1629,6 +1629,19 @@ 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; }