WARNING in drop

WARNING in drop_nlink (2)
Status: upstream: reported C repro on 2020/10/13 17:02
Reported-by: syzbot+651ca866e5e2b4b5095b@syzkaller.appspotmail.com
First crash: 142d, last: 44d

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

similar bugs (2):
Kernel	Title	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
linux-4.19	WARNING in drop_nlink	C			2	18d	143d	0/1	upstream: reported C repro on 2020/10/08 09:54
upstream	WARNING in drop_nlink	C	done	error	1	312d	308d	17/21	fixed on 2020/09/16 22:51

Sample crash report:

MINIX-fs: mounting unchecked file system, running fsck is recommended
------------[ cut here ]------------
WARNING: CPU: 0 PID: 6857 at fs/inode.c:303 drop_nlink+0xb9/0x100 fs/inode.c:303
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 6857 Comm: syz-executor857 Not tainted 5.9.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1d6/0x29e lib/dump_stack.c:118
 panic+0x2c0/0x800 kernel/panic.c:231
 __warn+0x227/0x250 kernel/panic.c:600
 report_bug+0x1b1/0x2e0 lib/bug.c:198
 handle_bug+0x42/0x80 arch/x86/kernel/traps.c:234
 exc_invalid_op+0x16/0x40 arch/x86/kernel/traps.c:254
 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
RIP: 0010:drop_nlink+0xb9/0x100 fs/inode.c:303
Code: 49 8b 1e 48 8d bb b8 07 00 00 be 08 00 00 00 e8 9d 46 ef ff f0 48 ff 83 b8 07 00 00 5b 41 5c 41 5e 41 5f 5d c3 e8 87 92 af ff <0f> 0b eb 8a 44 89 e1 80 e1 07 80 c1 03 38 c1 0f 8c 63 ff ff ff 4c
RSP: 0018:ffffc900010d7c50 EFLAGS: 00010293
RAX: ffffffff81c56b69 RBX: 1ffff11010a15c21 RCX: ffff88809190c1c0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff81c56aee R09: fffffbfff16c82b0
R10: fffffbfff16c82b0 R11: 0000000000000000 R12: ffff8880850ae108
R13: ffffc900010d7ca8 R14: ffff8880850ae0c0 R15: dffffc0000000000
 inode_dec_link_count include/linux/fs.h:2190 [inline]
 minix_rename+0x42b/0x7f0 fs/minix/namei.c:226
 vfs_rename+0xa5f/0x1500 fs/namei.c:4309
 do_renameat2+0x84a/0x1070 fs/namei.c:4456
 __do_sys_renameat fs/namei.c:4497 [inline]
 __se_sys_renameat fs/namei.c:4494 [inline]
 __x64_sys_renameat+0x9a/0xb0 fs/namei.c:4494
 do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x444729
Code: 8d d7 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 5b d7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffefa186b68 EFLAGS: 00000246 ORIG_RAX: 0000000000000108
RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 0000000000444729
RDX: 0000000000000009 RSI: 0000000020000500 RDI: 000000000000000a
RBP: 00000000006d0018 R08: 00000000004002e0 R09: 00000000004002e0
R10: 00000000200017c0 R11: 0000000000000246 R12: 0000000000402310
R13: 00000000004023a0 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..

Fix bisection attempts:
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro
ci-upstream-kasan-gce-smack-root	2021/01/15 23:16	upstream	82821be8	d81b165e	.config	log	report	syz	C
ci-upstream-kasan-gce-smack-root	2020/12/16 08:46	upstream	706451d4	d81b165e	.config	log	report	syz	C
ci-upstream-kasan-gce-smack-root	2020/11/08 23:09	upstream	15f5d201	d81b165e	.config	log	report	syz	C

Crashes (1):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Title
ci-upstream-kasan-gce-smack-root	2020/10/09 16:56	upstream	583090b1	d81b165e	.config	log	report	syz	C