[PATCH 5.15] io_uring: fix possible deadlock in io_register_iowq_max_workers()

[Hagar Hemdan <hagarhem@amazon.com>]

commit 73254a297c2dd094abec7c9efee32455ae875bdf upstream.

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@amazon.de>
Signed-off-by: Hagar Hemdan <hagarhem@amazon.com>
Link: https://lore.kernel.org/r/20240604130527.3597-1-hagarhem@amazon.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
[Hagar: Modified to apply on v5.15]
Signed-off-by: Hagar Hemdan <hagarhem@amazon.com>
---
 io_uring/io_uring.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index f1ab0cd98727..3dbc704c7001 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -10818,8 +10818,10 @@ static 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)))
@@ -10844,8 +10846,11 @@ static 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;
 }
-- 
2.40.1