Re: generic/068 crash on 5.18-rc2?

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Apr 13, 2022 at 03:50:32PM +0100, Matthew Wilcox wrote:
> On Tue, Apr 12, 2022 at 08:34:25PM -0700, Darrick J. Wong wrote:
> > Hmm.  Two nights in a row I've seen the following crash.  Has anyone
> > else seen this, or should I keep digging?  This is a fairly boring
> > x86_64 VM with a XFS v5 filesystem + rmapbt.
> 
> I have not seen this before.  I test with:
> MKFS_OPTIONS  -- -f -m reflink=1,rmapbt=1 -i sparse=1 -b size=1024 /dev/sdc
> 
> Maybe I should try a 4096 byte block size.
> 
> > mm/filemap.c:1653 is the BUG in:
> > 
> > void folio_end_writeback(struct folio *folio)
> > {
> > 	/*
> > 	 * folio_test_clear_reclaim() could be used here but it is an
> > 	 * atomic operation and overkill in this particular case.
> > 	 * Failing to shuffle a folio marked for immediate reclaim is
> > 	 * too mild a gain to justify taking an atomic operation penalty
> > 	 * at the end of every folio writeback.
> > 	 */
> > 	if (folio_test_reclaim(folio)) {
> > 		folio_clear_reclaim(folio);
> > 		folio_rotate_reclaimable(folio);
> > 	}
> > 
> > 	/*
> > 	 * Writeback does not hold a folio reference of its own, relying
> > 	 * on truncation to wait for the clearing of PG_writeback.
> > 	 * But here we must make sure that the folio is not freed and
> > 	 * reused before the folio_wake().
> > 	 */
> > 	folio_get(folio);
> > 	if (!__folio_end_writeback(folio))
> > >>>>		BUG();
> 
> Grr, that should have been a VM_BUG_ON_FOLIO(1, folio) so we get useful
> information about the folio (like whether it has an iop, or what order
> the folio is).  Can you make that change and try to reproduce?

> What's going on here is that we've called folio_end_writeback() on a
> folio which does not have the writeback flag set.  That _should_ be
> impossible, hence the use of BUG().  Either we've called
> folio_end_writeback() twice on the same folio, or we neglected to set
> the writeback flag on the folio.  I don't immediately see why either
> of those two things would happen.

Well, I made that change and rebased to -rc3 to see if reverting that
ZERO_PAGE thing would produce better results, I think I just got the
same crash.  Curiously, the only VM that died this time was the one
running the realtime configuration, but it's still generic/068:

FSTYP         -- xfs (debug)
PLATFORM      -- Linux/x86_64 oci-mtr28 5.18.0-rc3-djwx #rc3 SMP PREEMPT_DYNAMIC Sun Apr 17 14:42:49 PDT 2022
MKFS_OPTIONS  -- -f -rrtdev=/dev/sdb4 -llogdev=/dev/sdb2 -m reflink=0,rmapbt=0, -d rtinherit=1, /dev/sda4
MOUNT_OPTIONS -- -ortdev=/dev/sdb4 -ologdev=/dev/sdb2 /dev/sda4 /opt

I don't know if it'll help, but here's the sequence of tests that we
were running just prior to crashing:

generic/445      3s
generic/225      76s
xfs/306  22s
xfs/290  3s
generic/155     [not run] Reflink not supported by test filesystem type: xfs
generic/525      6s
generic/269      89s
generic/1206    [not run] xfs_io swapext -v vfs -s 64k -l 64k ioctl support is missing
xfs/504  198s
xfs/192 [not run] Reflink not supported by scratch filesystem type: xfs
xfs/303  1s
generic/346      6s
generic/512      5s
xfs/227  308s
generic/147     [not run] Reflink not supported by test filesystem type: xfs
generic/230     [not run] Quotas not supported on realtime test device
generic/008      4s
generic/108      4s
xfs/264  12s
generic/200     [not run] Reflink not supported by scratch filesystem type: xfs
generic/493     [not run] Dedupe not supported by scratch filesystem type: xfs
xfs/021  5s
generic/672     [not run] Reflink not supported by scratch filesystem type: xfs
xfs/493  5s
xfs/146  13s
xfs/315 [not run] Reflink not supported by scratch filesystem type: xfs
generic/068     

And the dmesg output:

run fstests generic/068 at 2022-04-17 16:57:16
XFS (sda4): Mounting V5 Filesystem
XFS (sda4): Ending clean mount
page:ffffea0004a39c40 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x128e71
flags: 0x17ff80000000000(node=0|zone=2|lastcpupid=0xfff)
raw: 017ff80000000000 0000000000000000 ffffffff00000203 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: VM_BUG_ON_FOLIO(((unsigned int) folio_ref_count(folio) + 127u <= 127u))
------------[ cut here ]------------
kernel BUG at include/linux/mm.h:1164!
invalid opcode: 0000 [#1] PREEMPT SMP
CPU: 3 PID: 1094085 Comm: 3:0 Tainted: G        W         5.18.0-rc3-djwx #rc3 0a707744ee7c555d54e50726c5b02515710a6aae
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20171121_152543-x86-ol7-builder-01.us.oracle.com-4.el7.1 04/01/2014
Workqueue: xfs-conv/sda4 xfs_end_io [xfs]
RIP: 0010:folio_end_writeback+0xd0/0x110
Code: 80 60 02 fb 48 89 ef e8 5e 6d 01 00 8b 45 34 83 c0 7f 83 f8 7f 0f 87 6a ff ff ff 48 c7 c6 40 c7 e2 81 48 89 ef e8 30 69 04 00 <0f> 0b 48 89 ee e8 b6 51 02 00 eb 9a 48 c7 c6 c0 ad e5 81 48 89 ef
RSP: 0018:ffffc900084f3d48 EFLAGS: 00010246
RAX: 000000000000005c RBX: 0000000000001000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81e56da3 RDI: 00000000ffffffff
RBP: ffffea0004a39c40 R08: 0000000000000000 R09: ffffffff8205fe40
R10: 0000000000017578 R11: 00000000000175f0 R12: 0000000000004000
R13: ffff88814dc5cd40 R14: 000000000000002e R15: ffffea0004a39c40
FS:  0000000000000000(0000) GS:ffff88843fd80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2b0ea47010 CR3: 000000043f00c000 CR4: 00000000001506a0
Call Trace:
 <TASK>
 iomap_finish_ioend+0x1ee/0x6a0
 iomap_finish_ioends+0x69/0x100
 xfs_end_ioend+0x5a/0x160 [xfs e8251de1111d7958449fd159d84af12a2afc12f2]
 xfs_end_io+0xb1/0xf0 [xfs e8251de1111d7958449fd159d84af12a2afc12f2]
 process_one_work+0x1df/0x3c0
 ? rescuer_thread+0x3b0/0x3b0
 worker_thread+0x53/0x3b0
 ? rescuer_thread+0x3b0/0x3b0
 kthread+0xea/0x110
 ? kthread_complete_and_exit+0x20/0x20
 ret_from_fork+0x1f/0x30
 </TASK>
Modules linked in: xfs dm_zero btrfs blake2b_generic xor lzo_compress lzo_decompress zlib_deflate raid6_pq zstd_compress dm_delay dm_snapshot dm_thin_pool dm_persistent_data dm_bio_prison dm_bufio dm_flakey libcrc32c xt_REDIRECT iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 auth_rpcgss oid_registry xt_tcpudp ip_set_hash_ip ip_set_hash_net xt_set ip_set_hash_mac ip_set nfnetlink ip6table_filter ip6_tables iptable_filter bfq sch_fq_codel ip_tables x_tables overlay nfsv4 af_packet [last unloaded: scsi_debug]
Dumping ftrace buffer:
   (ftrace buffer empty)
---[ end trace 0000000000000000 ]---
RIP: 0010:folio_end_writeback+0xd0/0x110
Code: 80 60 02 fb 48 89 ef e8 5e 6d 01 00 8b 45 34 83 c0 7f 83 f8 7f 0f 87 6a ff ff ff 48 c7 c6 40 c7 e2 81 48 89 ef e8 30 69 04 00 <0f> 0b 48 89 ee e8 b6 51 02 00 eb 9a 48 c7 c6 c0 ad e5 81 48 89 ef
RSP: 0018:ffffc900084f3d48 EFLAGS: 00010246
RAX: 000000000000005c RBX: 0000000000001000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81e56da3 RDI: 00000000ffffffff
RBP: ffffea0004a39c40 R08: 0000000000000000 R09: ffffffff8205fe40
R10: 0000000000017578 R11: 00000000000175f0 R12: 0000000000004000
R13: ffff88814dc5cd40 R14: 000000000000002e R15: ffffea0004a39c40
FS:  0000000000000000(0000) GS:ffff88843fd80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2b0ea47010 CR3: 000000043f00c000 CR4: 00000000001506a0

--D

> 
> > 
> > 
> > --D
> > 
> > run fstests generic/068 at 2022-04-12 17:57:11
> > XFS (sda3): Mounting V5 Filesystem
> > XFS (sda3): Ending clean mount
> > XFS (sda4): Mounting V5 Filesystem
> > XFS (sda4): Ending clean mount
> > ------------[ cut here ]------------
> > kernel BUG at mm/filemap.c:1653!
> > invalid opcode: 0000 [#1] PREEMPT SMP
> > CPU: 0 PID: 1349866 Comm: 0:116 Tainted: G        W         5.18.0-rc2-djwx #rc2 19cc48221d47ada6c8e5859639b6a0946c9a3777
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20171121_152543-x86-ol7-builder-01.us.oracle.com-4.el7.1 04/01/2014
> > Workqueue: xfs-conv/sda4 xfs_end_io [xfs]
> > RIP: 0010:folio_end_writeback+0x79/0x80
> > Code: d2 75 1d f0 ff 4d 34 74 0e 5d c3 f0 80 67 02 fb e8 ac 29 01 00 eb ad 48 89 ef 5d e9 a1 0f 01 00 48 89 ee e8 b9 e8 01 00 eb d9 <0f> 0b 0f 1f 44 00 00 0f 1f 44 00 00 53 48 89 fb e8 62 f7 ff ff 48
> > RSP: 0018:ffffc9000286fd50 EFLAGS: 00010246
> > RAX: 0000000000000000 RBX: ffffea0007376840 RCX: 000000000000000c
> > RDX: ffff88810d2de000 RSI: ffffffff81e55f0b RDI: ffff88810d2de000
> > RBP: ffffea0007376840 R08: ffffea000b82c308 R09: ffffea000b82c308
> > R10: 0000000000000001 R11: 000000000000000c R12: 0000000000000000
> > R13: 000000000000c000 R14: 0000000000000005 R15: 0000000000000001
> > FS:  0000000000000000(0000) GS:ffff88843fc00000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007f5b067d0000 CR3: 000000010d1bb000 CR4: 00000000001506b0
> > Call Trace:
> >  <TASK>
> >  iomap_finish_ioend+0x19e/0x560
> >  iomap_finish_ioends+0x69/0x100
> >  xfs_end_ioend+0x5a/0x160 [xfs 513857e2ae300a835ce1fbd8065a84dc5382e649]
> >  xfs_end_io+0xb1/0xf0 [xfs 513857e2ae300a835ce1fbd8065a84dc5382e649]
> >  process_one_work+0x1df/0x3c0
> >  ? rescuer_thread+0x3b0/0x3b0
> >  worker_thread+0x53/0x3b0
> >  ? rescuer_thread+0x3b0/0x3b0
> >  kthread+0xea/0x110
> >  ? kthread_complete_and_exit+0x20/0x20
> >  ret_from_fork+0x1f/0x30
> >  </TASK>
> > Modules linked in: dm_snapshot dm_bufio dm_zero dm_flakey xfs libcrc32c xt_REDIRECT iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 auth_rpcgss oid_registry xt_tcpudp ip_set_hash_ip ip_set_hash_net xt_set ip_set_hash_mac ip_set nfnetlink ip6table_filter ip6_tables iptable_filter bfq sch_fq_codel ip_tables x_tables overlay nfsv4 af_packet [last unloaded: scsi_debug]
> > Dumping ftrace buffer:
> >    (ftrace buffer empty)
> > ---[ end trace 0000000000000000 ]---
> > RIP: 0010:folio_end_writeback+0x79/0x80
> > Code: d2 75 1d f0 ff 4d 34 74 0e 5d c3 f0 80 67 02 fb e8 ac 29 01 00 eb ad 48 89 ef 5d e9 a1 0f 01 00 48 89 ee e8 b9 e8 01 00 eb d9 <0f> 0b 0f 1f 44 00 00 0f 1f 44 00 00 53 48 89 fb e8 62 f7 ff ff 48
> > RSP: 0018:ffffc9000286fd50 EFLAGS: 00010246
> > RAX: 0000000000000000 RBX: ffffea0007376840 RCX: 000000000000000c
> > RDX: ffff88810d2de000 RSI: ffffffff81e55f0b RDI: ffff88810d2de000
> > RBP: ffffea0007376840 R08: ffffea000b82c308 R09: ffffea000b82c308
> > R10: 0000000000000001 R11: 000000000000000c R12: 0000000000000000
> > R13: 000000000000c000 R14: 0000000000000005 R15: 0000000000000001
> > FS:  0000000000000000(0000) GS:ffff88843fc00000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007f4b94008278 CR3: 0000000101ac9000 CR4: 00000000001506b0
> >