Date:   Sat, 9 Jan 2021 16:40:57 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     syzbot <syzbot+99ed55100402022a6276@...kaller.appspotmail.com>,
        axboe@...nel.dk, io-uring@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        mingo@...nel.org, mingo@...hat.com, peterz@...radead.org,
        rostedt@...dmis.org, syzkaller-bugs@...glegroups.com,
        viro@...iv.linux.org.uk, will@...nel.org
Subject: Re: BUG: unable to handle kernel paging request in percpu_ref_exit

On 09/01/2021 16:27, syzbot wrote:
> 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
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+99ed55100402022a6276@...kaller.appspotmail.com
> Fixes: 4d004099a668 ("lockdep: Fix lockdep recursion")

Looks like the fixed ERR_PTR vs NULL issue.

#syz test: git://git.kernel.dk/linux-block d9d05217cb6990b9a56e13b56e7a1b71e2551f6c

> 
> 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@...glegroups.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
> 

-- 
Pavel Begunkov

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