kernel BUG at include/linux/fs.h:LINE!

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f6d5cb9e Linux 4.19.142
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=154338ae900000
kernel config: https://syzkaller.appspot.com/x/.config?x=30067df04d3254aa
dashboard link: https://syzkaller.appspot.com/bug?extid=71ff06f00f58329454b1
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=114373de900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+71ff06...@syzkaller.appspotmail.com

IPv6: ADDRCONF(NETDEV_CHANGE): veth0_to_batadv: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): macvtap0: link becomes ready
batman_adv: batadv0: Interface activated: batadv_slave_1
IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_batadv: link becomes ready
------------[ cut here ]------------
kernel BUG at include/linux/fs.h:2835!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 6713 Comm: syz-executor.0 Not tainted 4.19.142-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:i_readcount_dec include/linux/fs.h:2835 [inline]
RIP: 0010:__fput+0x7b6/0x890 fs/file_table.c:286
Code: f5 ff e9 ba fa ff ff 4c 89 e7 e8 05 79 f5 ff e9 9a f9 ff ff 48 c7 c7 f0 b5 ae 89 e8 f4 78 f5 ff e9 0e fd ff ff e8 9a 58 bf ff <0f> 0b 48 8b 7c 24 18 e8 6e 79 f5 ff e9 9f f8 ff ff 48 8b 7c 24 20
RSP: 0018:ffff888088ba7e38 EFLAGS: 00010293
RAX: ffff8880a0b5c080 RBX: ffff88809b22bb60 RCX: ffffffff81aa56db
RDX: 0000000000000000 RSI: ffffffff81aa58e6 RDI: 0000000000000005
RBP: ffff8880947d5840 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000005 R11: 0000000000000000 R12: ffff8880947d58bc
R13: ffff88809b22bd54 R14: 0000000000000000 R15: ffff888089458e20
FS: 00007f5d181a8700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056245882a0e8 CR3: 00000000971f9000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
task_work_run+0x148/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:193 [inline]
exit_to_usermode_loop+0x251/0x2a0 arch/x86/entry/common.c:167
prepare_exit_to_usermode arch/x86/entry/common.c:198 [inline]
syscall_return_slowpath arch/x86/entry/common.c:271 [inline]
do_syscall_64+0x538/0x620 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45d5b9
Code: 5d 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 2b b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f5d181a7c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000e9
RAX: 0000000000000000 RBX: 0000000000002ac0 RCX: 000000000045d5b9
RDX: 0000000000000004 RSI: 0000000000000001 RDI: 0000000000000005
RBP: 000000000118cf88 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000020000040 R11: 0000000000000246 R12: 000000000118cf4c
R13: 00007ffd2bb420ff R14: 00007f5d181a89c0 R15: 000000000118cf4c
Modules linked in:
---[ end trace 562c38db62d3f15d ]---
RIP: 0010:i_readcount_dec include/linux/fs.h:2835 [inline]
RIP: 0010:__fput+0x7b6/0x890 fs/file_table.c:286
Code: f5 ff e9 ba fa ff ff 4c 89 e7 e8 05 79 f5 ff e9 9a f9 ff ff 48 c7 c7 f0 b5 ae 89 e8 f4 78 f5 ff e9 0e fd ff ff e8 9a 58 bf ff <0f> 0b 48 8b 7c 24 18 e8 6e 79 f5 ff e9 9f f8 ff ff 48 8b 7c 24 20
RSP: 0018:ffff888088ba7e38 EFLAGS: 00010293
RAX: ffff8880a0b5c080 RBX: ffff88809b22bb60 RCX: ffffffff81aa56db
RDX: 0000000000000000 RSI: ffffffff81aa58e6 RDI: 0000000000000005
RBP: ffff8880947d5840 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000005 R11: 0000000000000000 R12: ffff8880947d58bc
R13: ffff88809b22bd54 R14: 0000000000000000 R15: ffff888089458e20
FS: 00007f5d181a8700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056245882a0e8 CR3: 00000000971f9000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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[syzbot]

syzbot suspects this issue was fixed by commit:

commit 37d933e8b41b83bb8278815e366aec5a542b7e31
Author: Al Viro <vi...@zeniv.linux.org.uk>
Date: Wed Sep 2 15:30:48 2020 +0000

fix regression in "epoll: Keep a reference on files added to the check list"

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=142bf5bd900000
start commit: f6d5cb9e Linux 4.19.142
git tree: linux-4.19.y

kernel config: https://syzkaller.appspot.com/x/.config?x=30067df04d3254aa
dashboard link: https://syzkaller.appspot.com/bug?extid=71ff06f00f58329454b1

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=114373de900000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: fix regression in "epoll: Keep a reference on files added to the check list"

For information about bisection process see: https://goo.gl/tpsmEJ#bisection