linux-kernel - [PATCH AUTOSEL 6.9 36/44] io_uring: fix possible deadlock in io_register_iowq_max

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Date: Tue, 18 Jun 2024 08:35:17 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Hagar Hemdan <hagarhem@...zon.com>,
	Maximilian Heyne <mheyne@...zon.de>,
	Jens Axboe <axboe@...nel.dk>,
	Sasha Levin <sashal@...nel.org>,
	io-uring@...r.kernel.org
Subject: [PATCH AUTOSEL 6.9 36/44] io_uring: fix possible deadlock in io_register_iowq_max_workers()

From: Hagar Hemdan <hagarhem@...zon.com>

[ Upstream commit 73254a297c2dd094abec7c9efee32455ae875bdf ]

The io_register_iowq_max_workers() function calls io_put_sq_data(),
which acquires the sqd->lock without releasing the uring_lock.
Similar to the commit 009ad9f0c6ee ("io_uring: drop ctx->uring_lock
before acquiring sqd->lock"), this can lead to a potential deadlock
situation.

To resolve this issue, the uring_lock is released before calling
io_put_sq_data(), and then it is re-acquired after the function call.

This change ensures that the locks are acquired in the correct
order, preventing the possibility of a deadlock.

Suggested-by: Maximilian Heyne <mheyne@...zon.de>
Signed-off-by: Hagar Hemdan <hagarhem@...zon.com>
Link: https://lore.kernel.org/r/20240604130527.3597-1-hagarhem@amazon.com
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 io_uring/register.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/io_uring/register.c b/io_uring/register.c
index 99c37775f974c..1ae8491e35abb 100644
--- a/io_uring/register.c
+++ b/io_uring/register.c
@@ -355,8 +355,10 @@ static __cold int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
 	}
 
 	if (sqd) {
+		mutex_unlock(&ctx->uring_lock);
 		mutex_unlock(&sqd->lock);
 		io_put_sq_data(sqd);
+		mutex_lock(&ctx->uring_lock);
 	}
 
 	if (copy_to_user(arg, new_count, sizeof(new_count)))
@@ -381,8 +383,10 @@ static __cold int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
 	return 0;
 err:
 	if (sqd) {
+		mutex_unlock(&ctx->uring_lock);
 		mutex_unlock(&sqd->lock);
 		io_put_sq_data(sqd);
+		mutex_lock(&ctx->uring_lock);
 	}
 	return ret;
 }
-- 
2.43.0