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ubi: check kthread_should_stop() after the setting of task state
commitd005f8c658
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:801c135ce7
("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>
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1 changed files with 13 additions and 0 deletions
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@ -1629,6 +1629,19 @@ int ubi_thread(void *u)
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!ubi->thread_enabled || ubi_dbg_is_bgt_disabled(ubi)) {
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!ubi->thread_enabled || ubi_dbg_is_bgt_disabled(ubi)) {
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set_current_state(TASK_INTERRUPTIBLE);
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set_current_state(TASK_INTERRUPTIBLE);
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spin_unlock(&ubi->wl_lock);
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spin_unlock(&ubi->wl_lock);
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/*
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* Check kthread_should_stop() after we set the task
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* state to guarantee that we either see the stop bit
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* and exit or the task state is reset to runnable such
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* that it's not scheduled out indefinitely and detects
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* the stop bit at kthread_should_stop().
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*/
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if (kthread_should_stop()) {
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set_current_state(TASK_RUNNING);
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break;
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}
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schedule();
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schedule();
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continue;
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continue;
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}
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}
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