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From: Pavel Begunkov <[email protected]>
To: Jens Axboe <[email protected]>, [email protected]
Cc: [email protected]
Subject: [PATCH v2 4/6] io_uring: dont kill fasync under completion_lock
Date: Mon,  4 Jan 2021 01:59:17 +0000	[thread overview]
Message-ID: <bf17089a9bcf65375a70b527fce21f56620f8d1d.1609725418.git.asml.silence@gmail.com> (raw)
In-Reply-To: <[email protected]>

      CPU0                    CPU1
       ----                    ----
  lock(&new->fa_lock);
                               local_irq_disable();
                               lock(&ctx->completion_lock);
                               lock(&new->fa_lock);
  <Interrupt>
    lock(&ctx->completion_lock);

 *** DEADLOCK ***

Move kill_fasync() out of io_commit_cqring() to io_cqring_ev_posted(),
so it doesn't hold completion_lock while doing it. That saves from the
reported deadlock, and it's just nice to shorten the locking time and
untangle nested locks (compl_lock -> wq_head::lock).

Reported-by: [email protected]
Signed-off-by: Pavel Begunkov <[email protected]>
---
 fs/io_uring.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2beb1e72302d..9c554adf3993 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1345,11 +1345,6 @@ static void __io_commit_cqring(struct io_ring_ctx *ctx)
 
 	/* order cqe stores with ring update */
 	smp_store_release(&rings->cq.tail, ctx->cached_cq_tail);
-
-	if (wq_has_sleeper(&ctx->cq_wait)) {
-		wake_up_interruptible(&ctx->cq_wait);
-		kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
-	}
 }
 
 static void io_put_identity(struct io_uring_task *tctx, struct io_kiocb *req)
@@ -1713,6 +1708,10 @@ static void io_cqring_ev_posted(struct io_ring_ctx *ctx)
 		wake_up(&ctx->sq_data->wait);
 	if (io_should_trigger_evfd(ctx))
 		eventfd_signal(ctx->cq_ev_fd, 1);
+	if (wq_has_sleeper(&ctx->cq_wait)) {
+		wake_up_interruptible(&ctx->cq_wait);
+		kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
+	}
 }
 
 static void io_cqring_ev_posted_iopoll(struct io_ring_ctx *ctx)
@@ -1723,6 +1722,10 @@ static void io_cqring_ev_posted_iopoll(struct io_ring_ctx *ctx)
 	}
 	if (io_should_trigger_evfd(ctx))
 		eventfd_signal(ctx->cq_ev_fd, 1);
+	if (wq_has_sleeper(&ctx->cq_wait)) {
+		wake_up_interruptible(&ctx->cq_wait);
+		kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
+	}
 }
 
 /* Returns true if there are no backlogged entries after the flush */
-- 
2.24.0


  parent reply	other threads:[~2021-01-04  2:03 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-04  1:59 [PATCH v2 0/6] bunch of random fixes Pavel Begunkov
2021-01-04  1:59 ` [PATCH v2 1/6] io_uring: drop file refs after task cancel Pavel Begunkov
2021-01-04  1:59 ` [PATCH v2 2/6] io_uring: cancel more aggressively in exit_work Pavel Begunkov
2021-01-04  1:59 ` [PATCH v2 3/6] io_uring: trigger eventfd for IOPOLL Pavel Begunkov
2021-01-04  1:59 ` Pavel Begunkov [this message]
2021-01-04  1:59 ` [PATCH v2 5/6] io_uring: synchronise IOPOLL on task_submit fail Pavel Begunkov
2021-01-04  1:59 ` [PATCH v2 6/6] io_uring: patch up IOPOLL overflow_flush sync Pavel Begunkov
2021-01-04 16:27 ` [PATCH v2 0/6] bunch of random fixes Pavel Begunkov

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