[PATCH] io_uring: fix CQ waiting timeout handling

[PATCH] io_uring: fix CQ waiting timeout handling

[Pavel Begunkov]

Jiffy to ktime CQ waiting conversion broke how we treat timeouts, in
particular we rearm it anew every time we get into
io_cqring_wait_schedule() without adjusting the timeout. Waiting for 2
CQEs and getting a task_work in the middle may double the timeout value,
or even worse in some cases task may wait indefinitely.

Cc: stable@vger.kernel.org
Fixes: 228339662b398 ("io_uring: don't convert to jiffies for waiting on timeouts")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/io_uring.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index adecdf65b130..71cd2edcc432 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -2401,7 +2401,7 @@ int io_run_task_work_sig(struct io_ring_ctx *ctx)
 /* when returns >0, the caller should retry */
 static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
 					  struct io_wait_queue *iowq,
-					  ktime_t timeout)
+					  ktime_t *timeout)
 {
 	int ret;
 	unsigned long check_cq;
@@ -2419,7 +2419,7 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
 		if (check_cq & BIT(IO_CHECK_CQ_DROPPED_BIT))
 			return -EBADR;
 	}
-	if (!schedule_hrtimeout(&timeout, HRTIMER_MODE_ABS))
+	if (!schedule_hrtimeout(timeout, HRTIMER_MODE_ABS))
 		return -ETIME;
 	return 1;
 }
@@ -2489,7 +2489,7 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
 		}
 		prepare_to_wait_exclusive(&ctx->cq_wait, &iowq.wq,
 						TASK_INTERRUPTIBLE);
-		ret = io_cqring_wait_schedule(ctx, &iowq, timeout);
+		ret = io_cqring_wait_schedule(ctx, &iowq, &timeout);
 		cond_resched();
 	} while (ret > 0);
 
-- 
2.38.1

Re: [PATCH] io_uring: fix CQ waiting timeout handling

[Pavel Begunkov]

On 1/5/23 10:44, Pavel Begunkov wrote:
> Jiffy to ktime CQ waiting conversion broke how we treat timeouts, in
> particular we rearm it anew every time we get into
> io_cqring_wait_schedule() without adjusting the timeout. Waiting for 2
> CQEs and getting a task_work in the middle may double the timeout value,
> or even worse in some cases task may wait indefinitely.

Wrong base, will send v2

-- 
Pavel Begunkov