Messages in this thread Patch in this message | | | From | Zhihao Cheng <> | Subject | [PATCH] ubi: check kthread_should_stop() after the setting of task state | Date | Mon, 1 Jun 2020 17:12:31 +0800 |
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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 --- drivers/mtd/ubi/wl.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c index 5146cce5fe32..a4d4343053d7 100644 --- a/drivers/mtd/ubi/wl.c +++ b/drivers/mtd/ubi/wl.c @@ -1628,6 +1628,19 @@ 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; } -- 2.25.4
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