From da3bb6fa23f1a4a2f0efa625621106d1d3e5892c Mon Sep 17 00:00:00 2001 From: Zhihao Cheng Date: Mon, 1 Jun 2020 17:12:31 +0800 Subject: [PATCH] ubi: check kthread_should_stop() after the setting of task state 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 Cc: Fixes: 801c135ce73d5df1ca ("UBI: Unsorted Block Images") Reported-by: syzbot+853639d0cb16c31c7a14@syzkaller.appspotmail.com Signed-off-by: Richard Weinberger Signed-off-by: Greg Kroah-Hartman --- 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 5d77a38dba54..7def041bbe48 100644 --- 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; }