virtio_blk - kernel BUG at drivers/virtio/virtio_ring.c:160!

[Brian Foster <bfoster@redhat.com>]

Hi all,

Hopefully this is the right list for this report...

I hit the following kernel bug reliably by running xfstests test
generic/234 against XFS using 10GB LVM test/scratch volumes on top of a
~100GB virtio_blk block device. The virt block device is file-backed on
the host.

>From the console:

------------[ cut here ]------------
kernel BUG at drivers/virtio/virtio_ring.c:160!
invalid opcode: 0000 [#1] SMP
Modules linked in: xfs libcrc32c cfg80211 rfkill snd_hda_codec_generic ppdev snd_hda_intel snd_hda_controller snd_hda_codec snd_hwdep snd_seq snd_seq_device snd_pcm snd_timer snd serio_raw virtio_balloon soundcore virtio_console parport_pc parport i2c_piix4 sunrpc virtio_blk virtio_net qxl drm_kms_helper ttm ata_generic virtio_pci virtio_ring drm virtio pata_acpi
CPU: 0 PID: 1442 Comm: xfsaild/dm-3 Not tainted 3.17.0+ #97
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
task: ffff8800c6483460 ti: ffff880118034000 task.ti: ffff880118034000
RIP: 0010:[<ffffffffa00729e5>]  [<ffffffffa00729e5>] virtqueue_add_sgs+0x415/0x430 [virtio_ring]
RSP: 0018:ffff880118037678  EFLAGS: 00010002
RAX: ffff88011808b000 RBX: ffff8801180377e8 RCX: 0000000000000003
RDX: ffffea0003667102 RSI: ffff8801180377d0 RDI: ffff880118037730
RBP: ffff8801180376e8 R08: ffff8800d78caf70 R09: 0000000000000020
R10: ffff8800c6483460 R11: ffff8800c6484050 R12: ffff8801180377e8
R13: 0000000000000002 R14: 0000000000000081 R15: 0000000000000020
FS:  0000000000000000(0000) GS:ffff88011ae00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007fffa85ff0c0 CR3: 0000000001e14000 CR4: 00000000000006f0
Stack:
 ffff880118037698 0000000000000304 ffff8800d78caf70 ffff8801180377d0
 0000000300000000 ffff88011808b000 ffff880118037730 ffff880000000002
 ffff8801180376e8 ffff8800d78caf70 ffff880118037730 0000000000000002
Call Trace:
 [<ffffffffa006a42f>] __virtblk_add_req+0xdf/0x1c0 [virtio_blk]
 [<ffffffffa006a5f2>] ? virtio_queue_rq+0xe2/0x280 [virtio_blk]
 [<ffffffffa006a616>] virtio_queue_rq+0x106/0x280 [virtio_blk]
 [<ffffffff813d71f1>] __blk_mq_run_hw_queue+0x1d1/0x350
 [<ffffffff813d7bb0>] blk_mq_run_hw_queue+0x70/0xa0
 [<ffffffff813d8a6d>] blk_mq_insert_requests+0xfd/0x2d0
 [<ffffffff813d9a2b>] blk_mq_flush_plug_list+0x13b/0x160
 [<ffffffff813cd5c1>] blk_flush_plug_list+0xc1/0x240
 [<ffffffff813d8f2a>] blk_sq_make_request+0x2ea/0x5d0
 [<ffffffff81656395>] ? dm_get_live_table+0x5/0xb0
 [<ffffffff813c7760>] generic_make_request+0xe0/0x130
 [<ffffffff813c7828>] submit_bio+0x78/0x160
 [<ffffffffa02ffcc6>] _xfs_buf_ioapply+0x2e6/0x420 [xfs]
 [<ffffffffa0300328>] ? __xfs_buf_delwri_submit+0x1d8/0x5b0 [xfs]
 [<ffffffffa02fff22>] xfs_buf_submit+0xd2/0x300 [xfs]
 [<ffffffffa0300328>] __xfs_buf_delwri_submit+0x1d8/0x5b0 [xfs]
 [<ffffffffa03021af>] ? xfs_buf_delwri_submit_nowait+0x2f/0x50 [xfs]
 [<ffffffffa03021af>] xfs_buf_delwri_submit_nowait+0x2f/0x50 [xfs]
 [<ffffffffa0340635>] xfsaild+0x275/0xe30 [xfs]
 [<ffffffffa03403c0>] ? xfs_trans_ail_cursor_first+0xb0/0xb0 [xfs]
 [<ffffffff810cda79>] kthread+0xf9/0x110
 [<ffffffff810cd980>] ? kthread_create_on_node+0x250/0x250
 [<ffffffff8182717c>] ret_from_fork+0x7c/0xb0
 [<ffffffff810cd980>] ? kthread_create_on_node+0x250/0x250
Code: ff 0f 1f 44 00 00 eb 84 48 8b 4d b8 8b 55 b0 48 c7 c6 19 42 07 a0 48 c7 c7 78 50 07 a0 31 c0 31 db e8 10 5d 3b e1 e9 4d fd ff ff <0f> 0b bb fb ff ff ff e9 41 fd ff ff 66 66 66 66 66 66 2e 0f 1f
RIP  [<ffffffffa00729e5>] virtqueue_add_sgs+0x415/0x430 [virtio_ring]
 RSP <ffff880118037678>
---[ end trace 823f74f9a11abe26 ]---

This occurs on the latest tot kernel (commit 0429fbc0bdc2) but appears
to originate sometime during the 3.16 development cycle. A bisect lands
on the following commit:

05f1dd53 block: add queue flag for disabling SG merging

To corroborate that, the appended diff appears to work around the
problem for me (included as a data point, not a fix, as I'm not familiar
with the block layer). Let me know if I can provide any more info,
thanks!

Brian

---8<---

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 0a58140..5861bd72 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -634,7 +634,7 @@ static int virtblk_probe(struct virtio_device *vdev)
 	vblk->tag_set.ops = &virtio_mq_ops;
 	vblk->tag_set.queue_depth = virtblk_queue_depth;
 	vblk->tag_set.numa_node = NUMA_NO_NODE;
-	vblk->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
+	vblk->tag_set.flags = BLK_MQ_F_SHOULD_MERGE|BLK_MQ_F_SG_MERGE;
 	vblk->tag_set.cmd_size =
 		sizeof(struct virtblk_req) +
 		sizeof(struct scatterlist) * sg_elems;