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authorZhihao Cheng <chengzhihao1@huawei.com>2020-06-01 17:12:31 +0800
committerRichard Weinberger <richard@nod.at>2020-09-17 22:55:59 +0200
commitd005f8c6588efcfbe88099b6edafc6f58c84a9c1 (patch)
treec3e63aef96f76c25486a0f2094f6678320222fc6 /drivers/mtd
parent58f6e78a65f1fcbf732f60a7478ccc99873ff3ba (diff)
downloadlinux-d005f8c6588efcfbe88099b6edafc6f58c84a9c1.tar.bz2
ubi: check kthread_should_stop() after the setting of task state
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>
Diffstat (limited to 'drivers/mtd')
-rw-r--r--drivers/mtd/ubi/wl.c13
1 files changed, 13 insertions, 0 deletions
diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index 42cac572f82d..7847de75a74c 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -1639,6 +1639,19 @@ 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;
}