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SubjectBUG: unable to handle kernel paging request in percpu_ref_exit
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Hello,

syzbot found the following issue on:

HEAD commit: 36bbbd0e Merge branch 'rcu/urgent' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=149afeeb500000
kernel config: https://syzkaller.appspot.com/x/.config?x=8aa30b9da402d224
dashboard link: https://syzkaller.appspot.com/bug?extid=99ed55100402022a6276
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10496f70d00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10cedf70d00000

The issue was bisected to:

commit 4d004099a668c41522242aa146a38cc4eb59cb1e
Author: Peter Zijlstra <peterz@infradead.org>
Date: Fri Oct 2 09:04:21 2020 +0000

lockdep: Fix lockdep recursion

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=106238f7500000
final oops: https://syzkaller.appspot.com/x/report.txt?x=126238f7500000
console output: https://syzkaller.appspot.com/x/log.txt?x=146238f7500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+99ed55100402022a6276@syzkaller.appspotmail.com
Fixes: 4d004099a668 ("lockdep: Fix lockdep recursion")

RBP: 0000000000000005 R08: 0000000000000001 R09: 0000000000401140
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402860
R13: 00000000004028f0 R14: 0000000000000000 R15: 0000000000000000
BUG: unable to handle page fault for address: fffffffffffffffc
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD b08f067 P4D b08f067 PUD b091067 PMD 0
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 8500 Comm: syz-executor191 Not tainted 5.11.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:percpu_ref_exit+0x2f/0x140 lib/percpu-refcount.c:130
Code: 54 55 53 48 89 fb e8 f0 fc b6 fd 48 8d 6b 08 48 b8 00 00 00 00 00 fc ff df 48 89 ea 48 c1 ea 03 80 3c 02 00 0f 85 d5 00 00 00 <4c> 8b 73 08 48 89 df e8 c5 fe ff ff 4d 85 f6 0f 84 b3 00 00 00 e8
RSP: 0018:ffffc9000126fcc8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: fffffffffffffff4 RCX: 0000000000000000
RDX: 1fffffffffffffff RSI: ffffffff83bb78b0 RDI: fffffffffffffff4
RBP: fffffffffffffffc R08: 0000000000000001 R09: ffffffff8ebda867
R10: fffffbfff1d7b50c R11: 0000000000000000 R12: 0000000000000000
R13: ffff88801adee000 R14: 0000000000000002 R15: fffffffffffffff4
FS: 000000000179f940(0000) GS:ffff8880b9e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffffffffffc CR3: 0000000020270000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
destroy_fixed_file_ref_node fs/io_uring.c:7703 [inline]
io_sqe_files_unregister+0x30b/0x770 fs/io_uring.c:7293
__io_uring_register fs/io_uring.c:9916 [inline]
__do_sys_io_uring_register+0x1185/0x4080 fs/io_uring.c:10000
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x444df9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 d5 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffeb192ade8 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab
RAX: ffffffffffffffda RBX: 00007ffeb192ae90 RCX: 0000000000444df9
RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000004
RBP: 0000000000000005 R08: 0000000000000001 R09: 0000000000401140
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402860
R13: 00000000004028f0 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
CR2: fffffffffffffffc
---[ end trace ed34d5d65a155c02 ]---
RIP: 0010:percpu_ref_exit+0x2f/0x140 lib/percpu-refcount.c:130
Code: 54 55 53 48 89 fb e8 f0 fc b6 fd 48 8d 6b 08 48 b8 00 00 00 00 00 fc ff df 48 89 ea 48 c1 ea 03 80 3c 02 00 0f 85 d5 00 00 00 <4c> 8b 73 08 48 89 df e8 c5 fe ff ff 4d 85 f6 0f 84 b3 00 00 00 e8
RSP: 0018:ffffc9000126fcc8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: fffffffffffffff4 RCX: 0000000000000000
RDX: 1fffffffffffffff RSI: ffffffff83bb78b0 RDI: fffffffffffffff4
RBP: fffffffffffffffc R08: 0000000000000001 R09: ffffffff8ebda867
R10: fffffbfff1d7b50c R11: 0000000000000000 R12: 0000000000000000
R13: ffff88801adee000 R14: 0000000000000002 R15: fffffffffffffff4
FS: 000000000179f940(0000) GS:ffff8880b9e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffffffffffc CR3: 0000000020270000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

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