Message-ID: <d7591a8b-f546-4742-a24c-6fefa876cf4c@linux.dev>
Date: Tue, 6 Aug 2024 11:31:16 -0700
From: Yonghong Song <yonghong.song@...ux.dev>
To: syzbot <syzbot+d6fb861ed047a275747a@...kaller.appspotmail.com>,
 andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
 daniel@...earbox.net, eddyz87@...il.com, haoluo@...gle.com,
 john.fastabend@...il.com, jolsa@...nel.org, kpsingh@...nel.org,
 linux-kernel@...r.kernel.org, martin.lau@...ux.dev, netdev@...r.kernel.org,
 sdf@...ichev.me, song@...nel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bpf?] BUG: spinlock recursion in bpf_lru_push_free


On 8/5/24 3:36 AM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    3d650ab5e7d9 selftests/bpf: Fix a btf_dump selftest failure

The failure is not due to this patch.

> git tree:       bpf-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13a4c1a1980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5efb917b1462a973
> dashboard link: https://syzkaller.appspot.com/bug?extid=d6fb861ed047a275747a
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/630e210de8d9/disk-3d650ab5.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/3576ca35748a/vmlinux-3d650ab5.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/5b33f099abfa/bzImage-3d650ab5.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+d6fb861ed047a275747a@...kaller.appspotmail.com
>
> BUG: spinlock recursion on CPU#1, syz.4.1173/11483

Actually this is a known issue and has been reported a few times in the past.

>   lock: 0xffff888046908300, .magic: dead4ead, .owner: syz.4.1173/11483, .owner_cpu: 1
> CPU: 1 UID: 0 PID: 11483 Comm: syz.4.1173 Not tainted 6.10.0-syzkaller-12666-g3d650ab5e7d9 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
> Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:93 [inline]
>   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:119
>   debug_spin_lock_before kernel/locking/spinlock_debug.c:87 [inline]
>   do_raw_spin_lock+0x227/0x370 kernel/locking/spinlock_debug.c:115
>   __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:111 [inline]
>   _raw_spin_lock_irqsave+0xe1/0x120 kernel/locking/spinlock.c:162
>   bpf_lru_list_push_free kernel/bpf/bpf_lru_list.c:318 [inline]
>   bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:538 [inline]
>   bpf_lru_push_free+0x1a7/0xb60 kernel/bpf/bpf_lru_list.c:561
>   htab_lru_map_delete_elem+0x613/0x700 kernel/bpf/hashtab.c:1475
>   bpf_prog_6f5f05285f674219+0x43/0x4c
>   bpf_dispatcher_nop_func include/linux/bpf.h:1252 [inline]
>   __bpf_prog_run include/linux/filter.h:691 [inline]
>   bpf_prog_run include/linux/filter.h:698 [inline]
>   __bpf_trace_run kernel/trace/bpf_trace.c:2406 [inline]
>   bpf_trace_run2+0x2ec/0x540 kernel/trace/bpf_trace.c:2447
>   trace_contention_begin+0x117/0x140 include/trace/events/lock.h:95

The tracepoint trace_contention_begin is the reason for spinlock recursion.
The trace_contention_begin is in
   queued_spin_lock_slowpath(...) {
     ...
     trace_contention_begin(lock, LCB_F_SPIN);
     ...
   }

And the bpf prog attached to trace_contention_begin() will go though spin_lock path again
and this may cause dead lock.


>   __pv_queued_spin_lock_slowpath+0x114/0xdc0 kernel/locking/qspinlock.c:402
>   pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:584 [inline]
>   queued_spin_lock_slowpath+0x42/0x50 arch/x86/include/asm/qspinlock.h:51
>   queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
>   lockdep_lock+0x1b0/0x2b0 kernel/locking/lockdep.c:143
>   graph_lock kernel/locking/lockdep.c:169 [inline]
>   lookup_chain_cache_add kernel/locking/lockdep.c:3803 [inline]
>   validate_chain+0x21d/0x5900 kernel/locking/lockdep.c:3836
>   __lock_acquire+0x137a/0x2040 kernel/locking/lockdep.c:5142
>   lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
>   __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
>   _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
>   htab_lock_bucket+0x1a4/0x370 kernel/bpf/hashtab.c:167
>   htab_lru_map_delete_node+0x161/0x840 kernel/bpf/hashtab.c:817
>   __bpf_lru_list_shrink_inactive kernel/bpf/bpf_lru_list.c:225 [inline]
>   __bpf_lru_list_shrink+0x156/0x9d0 kernel/bpf/bpf_lru_list.c:271
>   bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:345 [inline]
>   bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:452 [inline]
>   bpf_lru_pop_free+0xd84/0x1a70 kernel/bpf/bpf_lru_list.c:504
>   prealloc_lru_pop kernel/bpf/hashtab.c:308 [inline]
>   __htab_lru_percpu_map_update_elem+0x242/0x9b0 kernel/bpf/hashtab.c:1355
>   bpf_percpu_hash_update+0x11a/0x200 kernel/bpf/hashtab.c:2421
>   bpf_map_update_value+0x347/0x540 kernel/bpf/syscall.c:181
>   generic_map_update_batch+0x60d/0x900 kernel/bpf/syscall.c:1889
>   bpf_map_do_batch+0x3e0/0x690 kernel/bpf/syscall.c:5218
>   __sys_bpf+0x377/0x810
>   __do_sys_bpf kernel/bpf/syscall.c:5817 [inline]
>   __se_sys_bpf kernel/bpf/syscall.c:5815 [inline]
>   __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5815
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fed319779f9
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fed327ee048 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
> RAX: ffffffffffffffda RBX: 00007fed31b05f80 RCX: 00007fed319779f9
> RDX: 0000000000000038 RSI: 0000000020000580 RDI: 000000000000001a
> RBP: 00007fed319e58ee R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 000000000000000b R14: 00007fed31b05f80 R15: 00007ffcf9a1d7f8
>   </TASK>
>
>
> ---
> 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:
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>
> If the report is already addressed, let syzbot know by replying with:
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>
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>
> If the report is a duplicate of another one, reply with:
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>
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