Commit 73254a29 authored by Hagar Hemdan's avatar Hagar Hemdan Committed by Jens Axboe
Browse files

io_uring: fix possible deadlock in io_register_iowq_max_workers() 



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 009ad9f0 ("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: default avatarMaximilian Heyne <mheyne@amazon.de>
Signed-off-by: default avatarHagar Hemdan <hagarhem@amazon.com>
Link: https://lore.kernel.org/r/20240604130527.3597-1-hagarhem@amazon.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 91215f70

io_uring/register.c

+4 −0
Original line number Diff line number Diff line
@@ -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)))
@@ -380,8 +382,10 @@ 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;

}