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* [PATCH] io-wq: fix wakeup race when adding new work
@ 2021-08-30 14:02 Jens Axboe
  0 siblings, 0 replies; only message in thread
From: Jens Axboe @ 2021-08-30 14:02 UTC (permalink / raw)
  To: io-uring; +Cc: Andres Freund

When new work is added, io_wqe_enqueue() checks if we need to wake or
create a new worker. But that check is done outside the lock that
otherwise synchronizes us with a worker going to sleep, so we can end
up in the following situation:

CPU0                            CPU1
insert work
atomic_read(nr_running) != 0
no wakeup needed

Hold the wqe lock around the "need to wakeup" check. Then we can also get
rid of the temporary work_flags variable, as we know the work will remain
valid as long as we hold the lock.

Reported-by: Andres Freund <>
Signed-off-by: Jens Axboe <>

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 13aeb48a0964..cd9bd095fb1b 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -794,7 +794,7 @@ static void io_wqe_insert_work(struct io_wqe *wqe, struct io_wq_work *work)
 static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work)
 	struct io_wqe_acct *acct = io_work_get_acct(wqe, work);
-	int work_flags;
+	bool do_wake;
 	 * If io-wq is exiting for this task, or if the request has explicitly
@@ -806,14 +806,14 @@ static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work)
-	work_flags = work->flags;
 	io_wqe_insert_work(wqe, work);
 	wqe->flags &= ~IO_WQE_FLAG_STALLED;
+	do_wake = (work->flags & IO_WQ_WORK_CONCURRENT) ||
+			!atomic_read(&acct->nr_running);
-	if ((work_flags & IO_WQ_WORK_CONCURRENT) ||
-	    !atomic_read(&acct->nr_running))
+	if (do_wake)
 		io_wqe_wake_worker(wqe, acct);
Jens Axboe

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