WARNING in __writeback_inodes_sb

WARNING in __writeback_inodes_sb_nr
Status: upstream: reported syz repro on 2020/10/14 12:01
Reported-by: syzbot+b8ff83b095e45f39e27e@syzkaller.appspotmail.com
First crash: 139d, last: 84d

Cause bisection: the issue happens on the oldest tested release (bisect log)
Crash: WARNING in __writeback_inodes_sb_nr (log)
Repro: syz .config

Fix bisection: failed (bisect log)

similar bugs (1):
Kernel	Title	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
linux-4.19	WARNING in __writeback_inodes_sb_nr	C			22	18d	162d	0/1	upstream: reported C repro on 2020/09/20 14:27

Sample crash report:

BTRFS info (device loop0): disk space caching is enabled
BTRFS info (device loop0): has skinny extents
BTRFS info (device loop0): enabling ssd optimizations
BTRFS info (device loop0): checking UUID tree
------------[ cut here ]------------
WARNING: CPU: 0 PID: 8765 at fs/fs-writeback.c:2470 __writeback_inodes_sb_nr+0x229/0x280 fs/fs-writeback.c:2470
Modules linked in:
CPU: 0 PID: 8765 Comm: syz-executor.0 Not tainted 5.10.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__writeback_inodes_sb_nr+0x229/0x280 fs/fs-writeback.c:2470
Code: 48 8b 84 24 c0 00 00 00 65 48 2b 04 25 28 00 00 00 75 38 48 81 c4 c8 00 00 00 5b 5d 41 5c 41 5d 41 5e 41 5f c3 e8 97 33 a7 ff <0f> 0b e9 69 ff ff ff 4c 89 f7 e8 58 a9 e8 ff e9 ea fe ff ff 4c 89
RSP: 0018:ffffc9000210f6b0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 1ffff92000421ed7 RCX: ffffffff81c8d4f0
RDX: ffff88802bbfb480 RSI: ffffffff81c8d589 RDI: 0000000000000007
RBP: ffff88802b8e8000 R08: 0000000000000000 R09: ffff88802b8e8077
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffffc9000210f6d8 R14: 0000000000006400 R15: ffff88802b8e8168
FS:  00007f38ca733700(0000) GS:ffff8880b9e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd2d1962038 CR3: 000000002511a000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 btrfs_start_delalloc_flush fs/btrfs/transaction.c:1973 [inline]
 btrfs_commit_transaction+0x8da/0x2b60 fs/btrfs/transaction.c:2153
 btrfs_sync_file+0xe0f/0x1170 fs/btrfs/file.c:2328
 vfs_fsync_range+0x13a/0x220 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2723 [inline]
 btrfs_file_write_iter+0x1283/0x16d0 fs/btrfs/file.c:2075
 call_write_iter include/linux/fs.h:1887 [inline]
 do_iter_readv_writev+0x46f/0x740 fs/read_write.c:740
 do_iter_write+0x188/0x670 fs/read_write.c:866
 vfs_writev+0x1aa/0x2e0 fs/read_write.c:939
 do_pwritev fs/read_write.c:1036 [inline]
 __do_sys_pwritev fs/read_write.c:1083 [inline]
 __se_sys_pwritev fs/read_write.c:1078 [inline]
 __x64_sys_pwritev+0x231/0x310 fs/read_write.c:1078
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45deb9
Code: 0d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 db b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f38ca732c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000128
RAX: ffffffffffffffda RBX: 0000000000026480 RCX: 000000000045deb9
RDX: 0000000000000001 RSI: 00000000200014c0 RDI: 0000000000000003
RBP: 000000000118bf70 R08: 0000000000000020 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 000000000118bf2c
R13: 00007fffbba32e2f R14: 00007f38ca7339c0 R15: 000000000118bf2c

Crashes (2):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Title
ci-upstream-kasan-gce-root	2020/11/06 07:10	upstream	521b619a	64069d48	.config	log	report	syz
ci-upstream-kasan-gce-selinux-root	2020/10/13 06:20	upstream	bbf5c979	d32b0bbf	.config	log	report	syz