On 27.01.26 16:25, Johannes Thumshirn wrote:
When booting a Qemu VM with virtio-blk and KCSAN enabled, KCSAN emits
the following warning about a data-race in virtqueue_get_buf_ctx_split().
==================================================================
BUG: KCSAN: data-race in virtqueue_get_buf_ctx_split+0x6e/0x260
race at unknown origin, with read to 0xffff8881020f1942 of 2 bytes by task 1
on cpu 7:
virtqueue_get_buf_ctx_split+0x6e/0x260
virtqueue_get_buf+0x4b/0x60
__send_to_port+0x156/0x170
put_chars+0xcb/0x110
hvc_console_print+0x1d6/0x2a0
console_flush_one_record+0x3dd/0x510
console_unlock+0x8c/0x160
vprintk_emit+0x2fe/0x380
vprintk_default+0x1d/0x30
vprintk+0xe/0x20
_printk+0x4c/0x60
btrfs_test_raid_stripe_tree+0x25/0x90
btrfs_run_sanity_tests.cold+0xf1/0x13b
init_btrfs_fs+0x73/0x110
do_one_initcall+0x5b/0x2d0
kernel_init_freeable+0x2a2/0x340
kernel_init+0x1e/0x1b0
ret_from_fork+0x137/0x1b0
ret_from_fork_asm+0x1a/0x30
value changed: 0x0160 -> 0x0161
Reported by Kernel Concurrency Sanitizer on:
CPU: 7 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.19.0-rc7+ #219
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_split() with data_race() to silence
the warning.
Signed-off-by: Johannes Thumshirn <[email protected]>
---
drivers/virtio/virtio_ring.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index ddab68959671..1db27ee2d89f 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -808,8 +808,8 @@ static void detach_buf_split(struct vring_virtqueue *vq,
unsigned int head,
static bool more_used_split(const struct vring_virtqueue *vq)
This patches the split vring format, but does not touch the packed one.
What happens if you run the same test with the packed format? You can do
so by passing "packed=on" as argument to your -device parameter.
Alex
Amazon Web Services Development Center Germany GmbH
Tamara-Danz-Str. 13
10243 Berlin
Geschaeftsfuehrung: Christof Hellmis, Andreas Stieger
Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B
Sitz: Berlin
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