On Thu, Sep 12, 2024 at 04:46:28PM +0200, Marco Elver wrote: > On Thu, 12 Sept 2024 at 16:34, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > > On Thu, Sep 12, 2024 at 03:48:32PM +0200, Marco Elver wrote: > > > On Thu, 12 Sept 2024 at 13:03, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > > > > > > On Thu, Sep 12, 2024 at 01:11:21AM -0700, syzbot wrote: > > > > > Hello, > > > > > > > > > > syzbot found the following issue on: > > > > > > > > > > HEAD commit: 7c6a3a65ace7 minmax: reduce min/max macro expansion in ato.. > > > > > git tree: upstream > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1608e49f980000 > > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=1e7d02549be622b2 > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=8a02104389c2e0ef5049 > > > > > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40 > > > > > > > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > > > > > > > Downloadable assets: > > > > > disk image: https://storage.googleapis.com/syzbot-assets/a1f7496fa21f/disk-7c6a3a65.raw.xz > > > > > vmlinux: https://storage.googleapis.com/syzbot-assets/f423739e51a9/vmlinux-7c6a3a65.xz > > > > > kernel image: https://storage.googleapis.com/syzbot-assets/b65a0f38cbd7/bzImage-7c6a3a65.xz > > > > > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > > > Reported-by: syzbot+8a02104389c2e0ef5049@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > > > > > ================================================================== > > > > > BUG: KCSAN: data-race in virtqueue_disable_cb / vring_interrupt > > > > > > > > > > write to 0xffff88810285ef52 of 1 bytes by interrupt on cpu 0: > > > > > vring_interrupt+0x12b/0x180 drivers/virtio/virtio_ring.c:2591 > > > > > > > > > > > > Yes, it's racy! > > > > > > > > 2589: /* Just a hint for performance: so it's ok that this can be racy! */ > > > > 2590: if (vq->event) > > > > 2591: vq->event_triggered = true; > > > > > > > > > > > > Question: is there a way to annotate code to tell syzbot it's ok? > > > > > > In this case, "if (data_race(vq->event))" might be the right choice. > > > > No, vq->event is not racy. > > Oops - yes. > > > The race is between a write and a read of event_triggered. > > I think data_race tags a read, it can not tag a write, correct? > > data_race() takes an expression, so either read or write can be > enclosed - e.g. "data_race(vq->event_triggered = true);" works as > well. Ah, good to know. Yes, I see it is basically __kcsan_disable_current + __kcsan_enable_current. Will do. -- MST
