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From: Pavel Begunkov <[email protected]>
To: [email protected]
Cc: Jens Axboe <[email protected]>, [email protected]
Subject: [PATCH for-next 5/5] io_uring: remove ctx->refs pinning on enter
Date: Sat, 25 Jun 2022 11:53:02 +0100	[thread overview]
Message-ID: <a11c57ad33a1be53541fce90669c1b79cf4d8940.1656153286.git.asml.silence@gmail.com> (raw)
In-Reply-To: <[email protected]>

io_uring_enter() takes ctx->refs, which was previously preventing racing
with register quiesce. However, as register now doesn't touch the refs,
we can freely kill extra ctx pinning and rely on the fact that we're
holding a file reference preventing the ring from being destroyed.

Signed-off-by: Pavel Begunkov <[email protected]>
---
 io_uring/io_uring.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index e1e8dcd17df3..070ee9ec9ee7 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3049,14 +3049,10 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 			return -EBADF;
 		ret = -EOPNOTSUPP;
 		if (unlikely(!io_is_uring_fops(f.file)))
-			goto out_fput;
+			goto out;
 	}
 
-	ret = -ENXIO;
 	ctx = f.file->private_data;
-	if (unlikely(!percpu_ref_tryget(&ctx->refs)))
-		goto out_fput;
-
 	ret = -EBADFD;
 	if (unlikely(ctx->flags & IORING_SETUP_R_DISABLED))
 		goto out;
@@ -3141,10 +3137,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 					  &ctx->check_cq);
 		}
 	}
-
 out:
-	percpu_ref_put(&ctx->refs);
-out_fput:
 	fdput(f);
 	return ret;
 }
@@ -3730,11 +3723,10 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 	int ret;
 
 	/*
-	 * We're inside the ring mutex, if the ref is already dying, then
-	 * someone else killed the ctx or is already going through
-	 * io_uring_register().
+	 * We don't quiesce the refs for register anymore and so it can't be
+	 * dying as we're holding a file ref here.
 	 */
-	if (percpu_ref_is_dying(&ctx->refs))
+	if (WARN_ON_ONCE(percpu_ref_is_dying(&ctx->refs)))
 		return -ENXIO;
 
 	if (ctx->restricted) {
-- 
2.36.1


  parent reply	other threads:[~2022-06-25 10:53 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-25 10:52 [PATCH for-next 0/5] random 5.20 patches Pavel Begunkov
2022-06-25 10:52 ` [PATCH for-next 1/5] io_uring: improve io_fail_links() Pavel Begunkov
2022-06-25 10:52 ` [PATCH for-next 2/5] io_uring: fuse fallback_node and normal tw node Pavel Begunkov
2022-06-25 10:53 ` [PATCH for-next 3/5] io_uring: remove extra TIF_NOTIFY_SIGNAL check Pavel Begunkov
2022-06-25 10:53 ` [PATCH for-next 4/5] io_uring: don't check file ops of registered rings Pavel Begunkov
2022-06-25 10:53 ` Pavel Begunkov [this message]
2022-06-25 12:49 ` [PATCH for-next 0/5] random 5.20 patches Jens Axboe
2022-06-25 12:49 ` Jens Axboe

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