linux-kernel - [PATCH v2 3/5] io_uring: clear IORING_SETUP_SINGLE_ISSUER for IORING_SETUP

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250904170902.2624135-4-csander@purestorage.com>
Date: Thu,  4 Sep 2025 11:09:00 -0600
From: Caleb Sander Mateos <csander@...estorage.com>
To: Jens Axboe <axboe@...nel.dk>
Cc: io-uring@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Caleb Sander Mateos <csander@...estorage.com>
Subject: [PATCH v2 3/5] io_uring: clear IORING_SETUP_SINGLE_ISSUER for IORING_SETUP_SQPOLL

IORING_SETUP_SINGLE_ISSUER doesn't currently enable any optimizations,
but it will soon be used to avoid taking io_ring_ctx's uring_lock when
submitting from the single issuer task. If the IORING_SETUP_SQPOLL flag
is set, the SQ thread is the sole task issuing SQEs. However, other
tasks may make io_uring_register() syscalls, which must be synchronized
with SQE submission. So it wouldn't be safe to skip the uring_lock
around the SQ thread's submission even if IORING_SETUP_SINGLE_ISSUER is
set. Therefore, clear IORING_SETUP_SINGLE_ISSUER from the io_ring_ctx
flags if IORING_SETUP_SQPOLL is set.

Signed-off-by: Caleb Sander Mateos <csander@...estorage.com>
---
 io_uring/io_uring.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 42f6bfbb99d3..c7af9dc3d95a 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3724,10 +3724,19 @@ static int io_uring_sanitise_params(struct io_uring_params *p)
 	 */
 	if ((flags & (IORING_SETUP_CQE32|IORING_SETUP_CQE_MIXED)) ==
 	    (IORING_SETUP_CQE32|IORING_SETUP_CQE_MIXED))
 		return -EINVAL;

+	/*
+	 * If IORING_SETUP_SQPOLL is set, only the SQ thread issues SQEs,
+	 * but other threads may call io_uring_register() concurrently.
+	 * We still need uring_lock to synchronize these io_ring_ctx accesses,
+	 * so disable the single issuer optimizations.
+	 */
+	if (flags & IORING_SETUP_SQPOLL)
+		p->flags &= ~IORING_SETUP_SINGLE_ISSUER;
+
 	return 0;
 }

 int io_uring_fill_params(unsigned entries, struct io_uring_params *p)
 {
-- 
2.45.2