linux-kernel - [PATCH RFC 3/3] virtio: silence KCSAN warning in vring

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Message-ID: <20260127083926.865555-4-johannes.thumshirn@wdc.com>
Date: Tue, 27 Jan 2026 09:39:26 +0100
From: Johannes Thumshirn <johannes.thumshirn@....com>
To: virtualization@...ts.linux.dev
Cc: Alexander Graf <graf@...zon.com>,
	mst@...hat.com,
	jasowang@...hat.com,
	xuanzhuo@...ux.alibaba.com,
	eperezma@...hat.com,
	linux-kernel@...r.kernel.org,
	Johannes Thumshirn <johannes.thumshirn@....com>
Subject: [PATCH RFC 3/3] virtio: silence KCSAN warning in vring_interrupt

When booting a Qemu VM with virtio-blk and KCSAN enabled, KCSAN emits
the following warning about a data-race in vring_interrupt().

 ==================================================================
 BUG: KCSAN: data-race in vring_interrupt+0x125/0x1f0

 race at unknown origin, with read to 0xffff88810218d942 of 2 bytes by interrupt on cpu 7:
  vring_interrupt+0x125/0x1f0
  __handle_irq_event_percpu+0xaf/0x310
  handle_irq_event+0x76/0xf0
  handle_edge_irq+0x1fc/0x3e0
  __common_interrupt+0x79/0x160
  common_interrupt+0xa6/0xe0
  asm_common_interrupt+0x26/0x40
  pv_native_safe_halt+0x17/0x20
  default_idle+0x9/0x10
  default_idle_call+0x3c/0x110
  do_idle+0x166/0x190
  cpu_startup_entry+0x29/0x30
  start_secondary+0x114/0x140
  common_startup_64+0x129/0x138

 value changed: 0x3a3a -> 0x3a3b

 Reported by Kernel Concurrency Sanitizer on:
 CPU: 7 UID: 0 PID: 0 Comm: swapper/7 Not tainted 6.19.0-rc7+ #223 PREEMPT(none)
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-9.fc43 06/10/2025
 ==================================================================

This warning is likely a false positive as the change happens on the
virtio vring.

Annotate the return of more_used() with data_race() to silence the
warning.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@....com>
---
 drivers/virtio/virtio_ring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index d1033768b6cd..7fa8f2ebe94e 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -2695,7 +2695,7 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
-	if (!more_used(vq)) {
+	if (data_race(!more_used(vq))) {
 		pr_debug("virtqueue interrupt with no work for %p\n", vq);
 		return IRQ_NONE;
 	}
-- 
2.52.0