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From: Jens Axboe <axboe@kernel.dk>
To: io-uring@vger.kernel.org
Cc: Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 1/5] io-wq: fix queue stalling race
Date: Thu,  2 Sep 2021 13:25:16 -0600	[thread overview]
Message-ID: <20210902192520.326283-2-axboe@kernel.dk> (raw)
In-Reply-To: <20210902192520.326283-1-axboe@kernel.dk>

We need to set the stalled bit early, before we drop the lock for adding
us to the stall hash queue. If not, then we can race with new work being
queued between adding us to the stall hash and io_worker_handle_work()
marking us stalled.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io-wq.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index a94060b72f84..aa9656eb832e 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -436,8 +436,7 @@ static bool io_worker_can_run_work(struct io_worker *worker,
 }
 
 static struct io_wq_work *io_get_next_work(struct io_wqe *wqe,
-					   struct io_worker *worker,
-					   bool *stalled)
+					   struct io_worker *worker)
 	__must_hold(wqe->lock)
 {
 	struct io_wq_work_node *node, *prev;
@@ -475,10 +474,14 @@ static struct io_wq_work *io_get_next_work(struct io_wqe *wqe,
 	}
 
 	if (stall_hash != -1U) {
+		/*
+		 * Set this before dropping the lock to avoid racing with new
+		 * work being added and clearing the stalled bit.
+		 */
+		wqe->flags |= IO_WQE_FLAG_STALLED;
 		raw_spin_unlock(&wqe->lock);
 		io_wait_on_hash(wqe, stall_hash);
 		raw_spin_lock(&wqe->lock);
-		*stalled = true;
 	}
 
 	return NULL;
@@ -518,7 +521,6 @@ static void io_worker_handle_work(struct io_worker *worker)
 
 	do {
 		struct io_wq_work *work;
-		bool stalled;
 get_next:
 		/*
 		 * If we got some work, mark us as busy. If we didn't, but
@@ -527,12 +529,9 @@ static void io_worker_handle_work(struct io_worker *worker)
 		 * can't make progress, any work completion or insertion will
 		 * clear the stalled flag.
 		 */
-		stalled = false;
-		work = io_get_next_work(wqe, worker, &stalled);
+		work = io_get_next_work(wqe, worker);
 		if (work)
 			__io_worker_busy(wqe, worker, work);
-		else if (stalled)
-			wqe->flags |= IO_WQE_FLAG_STALLED;
 
 		raw_spin_unlock(&wqe->lock);
 		if (!work)
-- 
2.33.0


  reply	other threads:[~2021-09-02 19:25 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-02 19:25 [PATCHSET 0/5] io-wq fixes Jens Axboe
2021-09-02 19:25 ` Jens Axboe [this message]
2021-09-02 19:25 ` [PATCH 2/5] io-wq: split bounded and unbounded work into separate lists Jens Axboe
2021-09-02 19:25 ` [PATCH 3/5] io-wq: only exit on fatal signals Jens Axboe
2021-09-02 19:25 ` [PATCH 4/5] io-wq: get rid of FIXED worker flag Jens Axboe
2021-09-02 19:25 ` [PATCH 5/5] io-wq: make worker creation resilient against signals Jens Axboe

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