WARNING in percpu_ref_exit (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7ddd09fc Add linux-next specific files for 20191220
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12a18cc6e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=f183b01c3088afc6
dashboard link: https://syzkaller.appspot.com/bug?extid=8c4a14856e657b43487c
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14b8f351e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14b51925e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8c4a14...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 1 PID: 11482 at lib/percpu-refcount.c:111
percpu_ref_exit+0xab/0xd0 lib/percpu-refcount.c:111
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 11482 Comm: syz-executor051 Not tainted
5.5.0-rc2-next-20191220-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+0x197/0x210 lib/dump_stack.c:118
panic+0x2e3/0x75c kernel/panic.c:221
__warn.cold+0x2f/0x3e kernel/panic.c:582
report_bug+0x289/0x300 lib/bug.c:195
fixup_bug arch/x86/kernel/traps.c:174 [inline]
fixup_bug arch/x86/kernel/traps.c:169 [inline]
do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:267
do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:286
invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
RIP: 0010:percpu_ref_exit+0xab/0xd0 lib/percpu-refcount.c:111
Code: 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 75 1d 48 c7 43 08 03 00
00 00 e8 01 41 e5 fd 5b 41 5c 41 5d 5d c3 e8 f5 40 e5 fd <0f> 0b eb bf 4c
89 ef e8 29 2c 23 fe eb d9 e8 82 2b 23 fe eb a7 4c
RSP: 0018:ffffc9000cb17968 EFLAGS: 00010293
RAX: ffff8880a3390640 RBX: ffff8880a83a8010 RCX: ffffffff83901432
RDX: 0000000000000000 RSI: ffffffff8390149b RDI: ffff8880a83a8028
RBP: ffffc9000cb17980 R08: ffff8880a3390640 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000607f51435750
R13: ffff8880a83a8018 R14: ffff888097b95000 R15: ffff888097b95228
io_sqe_files_unregister+0x7d/0x2f0 fs/io_uring.c:4623
io_ring_ctx_free fs/io_uring.c:5575 [inline]
io_ring_ctx_wait_and_kill+0x430/0x9a0 fs/io_uring.c:5644
io_uring_release+0x42/0x50 fs/io_uring.c:5652
__fput+0x2ff/0x890 fs/file_table.c:280
____fput+0x16/0x20 fs/file_table.c:313
task_work_run+0x145/0x1c0 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0x909/0x2f20 kernel/exit.c:797
do_group_exit+0x135/0x360 kernel/exit.c:895
get_signal+0x47c/0x24f0 kernel/signal.c:2734
do_signal+0x87/0x1700 arch/x86/kernel/signal.c:815
exit_to_usermode_loop+0x286/0x380 arch/x86/entry/common.c:160
prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
do_syscall_64+0x676/0x790 arch/x86/entry/common.c:304
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4468f9
Code: e8 0c e8 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 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 5b 07 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f7ef700ddb8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00000000006dbc38 RCX: 00000000004468f9
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00000000006dbc38
RBP: 00000000006dbc30 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc3c
R13: 00007fff8371e42f R14: 00007f7ef700e9c0 R15: 0000000000000001
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This bug is generated by a bot. It may contain errors.
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syzbot can test patches for this bug, for details see:
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[syzbot]

syzbot has bisected this bug to:

commit cbb537634780172137459dead490d668d437ef4d
Author: Jens Axboe <ax...@kernel.dk>
Date: Mon Dec 9 18:22:50 2019 +0000

io_uring: avoid ring quiesce for fixed file set unregister and update

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1118aac1e00000
start commit: 7ddd09fc Add linux-next specific files for 20191220
git tree: linux-next
final crash: https://syzkaller.appspot.com/x/report.txt?x=1318aac1e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1518aac1e00000

kernel config: https://syzkaller.appspot.com/x/.config?x=f183b01c3088afc6
dashboard link: https://syzkaller.appspot.com/bug?extid=8c4a14856e657b43487c

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14b8f351e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14b51925e00000

Reported-by: syzbot+8c4a14...@syzkaller.appspotmail.com
Fixes: cbb537634780 ("io_uring: avoid ring quiesce for fixed file set
unregister and update")

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

[Hillf Danton]

On Sat, 21 Dec 2019 00:05:07 -0800

> Hello,
>
> syzbot found the following crash on:
>

> HEAD commit: 7ddd09fc Add linux-next specific files for 20191220
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=12a18cc6e00000

> kernel config: https://syzkaller.appspot.com/x/.config?x=f183b01c3088afc6
> dashboard link: https://syzkaller.appspot.com/bug?extid=8c4a14856e657b43487c

> compiler: gcc (GCC) 9.0.0 20181231 (experimental)

> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14b8f351e00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14b51925e00000
>

Flush work before killing.

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4618,10 +4618,10 @@ static int io_sqe_files_unregister(struc
if (!data)
return -ENXIO;

+ flush_work(&data->ref_work);
percpu_ref_kill_and_confirm(&data->refs, io_file_ref_kill);
wait_for_completion(&data->done);
percpu_ref_exit(&data->refs);
- flush_work(&data->ref_work);

__io_sqe_files_unregister(ctx);
nr_tables = DIV_ROUND_UP(ctx->nr_user_files, IORING_MAX_FILES_TABLE);

[Jens Axboe]

Oh indeed, good catch! Thanks, I'll fold this in.

--
Jens Axboe

[Eric Biggers]

Hi Jens, this bug is still occurring. See the syzbot dashboard:
https://syzkaller.appspot.com/bug?extid=8c4a14856e657b43487c

Here's a crash on upstream commit 7ae77150d94d (Fri Jun 5 12:39:30 2020 -0700):
https://syzkaller.appspot.com/text?tag=CrashReport&x=1754d169100000

- Eric

[syzbot]

syzbot suspects this issue was fixed by commit:

commit c1e2148f8ecb26863b899d402a823dab8e26efd1
Author: Jens Axboe <ax...@kernel.dk>
Date: Wed Mar 4 14:25:50 2020 +0000

io_uring: free fixed_file_data after RCU grace period

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=161ea46e500000
start commit: 63849c8f Merge tag 'linux-kselftest-5.6-rc5' of git://git...
git tree: upstream
kernel config: https://syzkaller.appspot.com/x/.config?x=4527d1e2fb19fd5c
dashboard link: https://syzkaller.appspot.com/bug?extid=8c4a14856e657b43487c
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13c30061e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1251b731e00000

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

#syz fix: io_uring: free fixed_file_data after RCU grace period

[Dmitry Vyukov]