Re: [syzbot] [bpf?] possible deadlock in __bpf_ringbuf_reserve

[Jiri Olsa]

On Tue, Mar 12, 2024 at 09:41:26AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    df4793505abd Merge tag 'net-6.8-rc8' of git://git.kernel.o..
> git tree:       bpf
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=11fd0092180000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c11c5c676adb61f0
> dashboard link: https://syzkaller.appspot.com/bug?extid=850aaf14624dc0c6d366
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1509c4ae180000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10babc01180000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/d2e80ee1112b/disk-df479350.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b35ea54cd190/vmlinux-df479350.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/59f69d999ad2/bzImage-df479350.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+850aaf14624dc0c6d366@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ============================================
> WARNING: possible recursive locking detected
> 6.8.0-rc7-syzkaller-gdf4793505abd #0 Not tainted
> --------------------------------------------
> strace-static-x/5063 is trying to acquire lock:
> ffffc900096f10d8 (&rb->spinlock){-.-.}-{2:2}, at: __bpf_ringbuf_reserve+0x211/0x4f0 kernel/bpf/ringbuf.c:424
> 
> but task is already holding lock:
> ffffc900098410d8 (&rb->spinlock){-.-.}-{2:2}, at: __bpf_ringbuf_reserve+0x211/0x4f0 kernel/bpf/ringbuf.c:424
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
> 
>        CPU0
>        ----
>   lock(&rb->spinlock);
>   lock(&rb->spinlock);
> 
>  *** DEADLOCK ***
> 
>  May be due to missing lock nesting notation
> 
> 4 locks held by strace-static-x/5063:
>  #0: ffff88807857e068 (&pipe->mutex/1){+.+.}-{3:3}, at: __pipe_lock fs/pipe.c:103 [inline]
>  #0: ffff88807857e068 (&pipe->mutex/1){+.+.}-{3:3}, at: pipe_write+0x1cc/0x1a40 fs/pipe.c:465
>  #1: ffffffff8e130be0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:298 [inline]
>  #1: ffffffff8e130be0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:750 [inline]
>  #1: ffffffff8e130be0 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2380 [inline]
>  #1: ffffffff8e130be0 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run2+0x114/0x420 kernel/trace/bpf_trace.c:2420
>  #2: ffffc900098410d8 (&rb->spinlock){-.-.}-{2:2}, at: __bpf_ringbuf_reserve+0x211/0x4f0 kernel/bpf/ringbuf.c:424
>  #3: ffffffff8e130be0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:298 [inline]
>  #3: ffffffff8e130be0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:750 [inline]
>  #3: ffffffff8e130be0 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2380 [inline]
>  #3: ffffffff8e130be0 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run2+0x114/0x420 kernel/trace/bpf_trace.c:2420
> 
> stack backtrace:
> CPU: 0 PID: 5063 Comm: strace-static-x Not tainted 6.8.0-rc7-syzkaller-gdf4793505abd #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x1e7/0x2e0 lib/dump_stack.c:106
>  check_deadlock kernel/locking/lockdep.c:3062 [inline]
>  validate_chain+0x15c0/0x58e0 kernel/locking/lockdep.c:3856
>  __lock_acquire+0x1345/0x1fd0 kernel/locking/lockdep.c:5137
>  lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754
>  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>  _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
>  __bpf_ringbuf_reserve+0x211/0x4f0 kernel/bpf/ringbuf.c:424
>  ____bpf_ringbuf_reserve kernel/bpf/ringbuf.c:459 [inline]
>  bpf_ringbuf_reserve+0x5c/0x70 kernel/bpf/ringbuf.c:451
>  bpf_prog_9efe54833449f08e+0x2d/0x47
>  bpf_dispatcher_nop_func include/linux/bpf.h:1231 [inline]
>  __bpf_prog_run include/linux/filter.h:651 [inline]
>  bpf_prog_run include/linux/filter.h:658 [inline]
>  __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]

hum, scratching my head how this could passed through the prog->active check,
will try to reproduce

jirka

>  bpf_trace_run2+0x204/0x420 kernel/trace/bpf_trace.c:2420
>  __traceiter_contention_end+0x7b/0xb0 include/trace/events/lock.h:122
>  trace_contention_end+0xf6/0x120 include/trace/events/lock.h:122
>  __pv_queued_spin_lock_slowpath+0x939/0xc60 kernel/locking/qspinlock.c:560
>  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]
>  do_raw_spin_lock+0x271/0x370 kernel/locking/spinlock_debug.c:116
>  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:111 [inline]
>  _raw_spin_lock_irqsave+0xe1/0x120 kernel/locking/spinlock.c:162
>  __bpf_ringbuf_reserve+0x211/0x4f0 kernel/bpf/ringbuf.c:424
>  ____bpf_ringbuf_reserve kernel/bpf/ringbuf.c:459 [inline]
>  bpf_ringbuf_reserve+0x5c/0x70 kernel/bpf/ringbuf.c:451
>  bpf_prog_9efe54833449f08e+0x2d/0x47
>  bpf_dispatcher_nop_func include/linux/bpf.h:1231 [inline]
>  __bpf_prog_run include/linux/filter.h:651 [inline]
>  bpf_prog_run include/linux/filter.h:658 [inline]
>  __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
>  bpf_trace_run2+0x204/0x420 kernel/trace/bpf_trace.c:2420
>  __traceiter_contention_end+0x7b/0xb0 include/trace/events/lock.h:122
>  trace_contention_end+0xd7/0x100 include/trace/events/lock.h:122
>  __mutex_lock_common kernel/locking/mutex.c:617 [inline]
>  __mutex_lock+0x2e4/0xd70 kernel/locking/mutex.c:752
>  __pipe_lock fs/pipe.c:103 [inline]
>  pipe_write+0x1cc/0x1a40 fs/pipe.c:465
>  call_write_iter include/linux/fs.h:2087 [inline]
>  new_sync_write fs/read_write.c:497 [inline]
>  vfs_write+0xa81/0xcb0 fs/read_write.c:590
>  ksys_write+0x1a0/0x2c0 fs/read_write.c:643
>  do_syscall_64+0xf9/0x240
>  entry_SYSCALL_64_after_hwframe+0x6f/0x77
> RIP: 0033:0x4e8593
> Code: c7 c2 a8 ff ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 64 8b 04 25 18 00 00 00 85 c0 75 14 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 55 c3 0f 1f 40 00 48 83 ec 28 48 89 54 24 18
> RSP: 002b:00007ffeda768928 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 0000000000000012 RCX: 00000000004e8593
> RDX: 0000000000000012 RSI: 0000000000817140 RDI: 0000000000000002
> RBP: 0000000000817140 R08: 0000000000000010 R09: 0000000000000090
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000012
> R13: 000000000063f460 R14: 0000000000000012 R15: 0000000000000001
>  </TASK>
> 
> 
> ---
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