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X-CSE-ConnectionGUID: iMsomQdDQnSepv8GyCpz7Q== X-CSE-MsgGUID: O1hFpnX7QVqbD2R6k+Hevw== X-IronPort-AV: E=Sophos;i="6.21,256,1763395200"; d="scan'208";a="136124512" Received: from uls-op-cesaip01.wdc.com (HELO uls-op-cesaep01.wdc.com) ([199.255.45.14]) by ob1.hgst.iphmx.com with ESMTP; 27 Jan 2026 16:39:36 +0800 IronPort-SDR: 697879c8_W6tvSW3PlfqkuKfyAsImKr1HsSL6ERFVieRbXeqdB++kZGS MV4yTdOYUQ6ICUgF/nNAgQ5L/PlSmHpZfe4grFQ== Received: from uls-op-cesaip02.wdc.com ([10.248.3.37]) by uls-op-cesaep01.wdc.com with ESMTP/TLS/ECDHE-RSA-AES128-GCM-SHA256; 27 Jan 2026 00:39:36 -0800 WDCIronportException: Internal Received: from 5cg02580n2.ad.shared (HELO neo.wdc.com) ([10.224.28.78]) by uls-op-cesaip02.wdc.com with ESMTP; 27 Jan 2026 00:39:34 -0800 From: Johannes Thumshirn To: virtualization@lists.linux.dev Cc: Alexander Graf , mst@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, linux-kernel@vger.kernel.org, Johannes Thumshirn Subject: [PATCH RFC 2/3] virtio: silence KCSAN warning in virtqueue_get_buf_ctx_split Date: Tue, 27 Jan 2026 09:39:25 +0100 Message-ID: <20260127083926.865555-3-johannes.thumshirn@wdc.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260127083926.865555-1-johannes.thumshirn@wdc.com> References: <20260127083926.865555-1-johannes.thumshirn@wdc.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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(). =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 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 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 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 --- 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 5f8c8254bb6c..d1033768b6cd 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -829,7 +829,7 @@ static void *virtqueue_get_buf_ctx_split(struct virtque= ue *_vq, return NULL; } =20 - if (!more_used_split(vq)) { + if (data_race(!more_used_split(vq))) { pr_debug("No more buffers in queue\n"); END_USE(vq); return NULL; --=20 2.52.0