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

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, Mar 12, 2024 at 10:02:27PM +0100, Jiri Olsa wrote:
> 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@syzkaller.appspotmail.com
> > 
> > ============================================
> > 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,

nah could be 2 instances of the same program, got confused by the tag

trace_contention_end
  __bpf_trace_run(prog1)
    bpf_prog_9efe54833449f08e
      bpf_ringbuf_reserve
        trace_contention_end
          __bpf_trace_run(prog1)  prog1->active check fails
          __bpf_trace_run(prog2) 
            bpf_prog_9efe54833449f08e
              bpf_ringbuf_reserve
                lockup

we had similar issue in [1] and we replaced the lock with extra buffers,
not sure that's possible in bpf_ringbuf_reserve

jirka


[1] e2bb9e01d589 bpf: Remove trace_printk_lock

> 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>
> > 
> > 
> > ---
> > 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.
> > 
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> > 
> > If the report is already addressed, let syzbot know by replying with:
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> > 
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> > 
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> > 
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