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

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in hrtimer_start_range_ns

======================================================
WARNING: possible circular locking dependency detected
6.8.0-syzkaller-08951-gfe46a7dd189e-dirty #0 Not tainted
------------------------------------------------------
syz-executor.0/5489 is trying to acquire lock:
ffff8880b952c8d8 (hrtimer_bases.lock){-.-.}-{2:2}, at: lock_hrtimer_base kernel/time/hrtimer.c:175 [inline]
ffff8880b952c8d8 (hrtimer_bases.lock){-.-.}-{2:2}, at: hrtimer_start_range_ns+0xdf/0xc60 kernel/time/hrtimer.c:1303

but task is already holding lock:
ffff88802195e9f8 (&trie->lock){-.-.}-{2:2}, at: trie_update_elem+0xcb/0xc10 kernel/bpf/lpm_trie.c:324

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&trie->lock){-.-.}-{2:2}:
       lock_acquire+0x1e4/0x530 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
       trie_delete_elem+0x96/0x6a0 kernel/bpf/lpm_trie.c:451
       0xffffffffa00060ce
       bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
       __bpf_prog_run include/linux/filter.h:657 [inline]
       bpf_prog_run include/linux/filter.h:664 [inline]
       __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
       bpf_trace_run2+0x204/0x420 kernel/trace/bpf_trace.c:2420
       trace_hrtimer_start include/trace/events/timer.h:222 [inline]
       debug_activate kernel/time/hrtimer.c:479 [inline]
       enqueue_hrtimer+0x335/0x3a0 kernel/time/hrtimer.c:1090
       __hrtimer_start_range_ns kernel/time/hrtimer.c:1265 [inline]
       hrtimer_start_range_ns+0xaa0/0xc60 kernel/time/hrtimer.c:1305
       futex_wait_queue+0xb0/0x1d0 kernel/futex/waitwake.c:357
       __futex_wait+0x17f/0x320 kernel/futex/waitwake.c:669
       futex_wait+0x101/0x360 kernel/futex/waitwake.c:697
       do_futex+0x33b/0x560 kernel/futex/syscalls.c:102
       __do_sys_futex kernel/futex/syscalls.c:179 [inline]
       __se_sys_futex+0x3f9/0x480 kernel/futex/syscalls.c:160
       do_syscall_64+0xfb/0x240
       entry_SYSCALL_64_after_hwframe+0x6d/0x75

-> #0 (hrtimer_bases.lock){-.-.}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
       __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
       lock_acquire+0x1e4/0x530 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
       lock_hrtimer_base kernel/time/hrtimer.c:175 [inline]
       hrtimer_start_range_ns+0xdf/0xc60 kernel/time/hrtimer.c:1303
       hrtimer_start include/linux/hrtimer.h:275 [inline]
       run_page_cache_worker kernel/rcu/tree.c:3342 [inline]
       kvfree_call_rcu+0x60e/0x7c0 kernel/rcu/tree.c:3447
       trie_update_elem+0x819/0xc10 kernel/bpf/lpm_trie.c:385
       bpf_map_update_value+0x4d3/0x540 kernel/bpf/syscall.c:203
       generic_map_update_batch+0x60d/0x900 kernel/bpf/syscall.c:1876
       bpf_map_do_batch+0x3e0/0x690 kernel/bpf/syscall.c:5145
       __sys_bpf+0x377/0x810
       __do_sys_bpf kernel/bpf/syscall.c:5738 [inline]
       __se_sys_bpf kernel/bpf/syscall.c:5736 [inline]
       __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5736
       do_syscall_64+0xfb/0x240
       entry_SYSCALL_64_after_hwframe+0x6d/0x75

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&trie->lock);
                               lock(hrtimer_bases.lock);
                               lock(&trie->lock);
  lock(hrtimer_bases.lock);

 *** DEADLOCK ***

3 locks held by syz-executor.0/5489:
 #0: ffffffff8e132020 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:298 [inline]
 #0: ffffffff8e132020 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:750 [inline]
 #0: ffffffff8e132020 (rcu_read_lock){....}-{1:2}, at: bpf_map_update_value+0x3c4/0x540 kernel/bpf/syscall.c:202
 #1: ffff88802195e9f8 (&trie->lock){-.-.}-{2:2}, at: trie_update_elem+0xcb/0xc10 kernel/bpf/lpm_trie.c:324
 #2: ffff8880b9529470 (krc.lock){....}-{2:2}, at: krc_this_cpu_lock kernel/rcu/tree.c:2960 [inline]
 #2: ffff8880b9529470 (krc.lock){....}-{2:2}, at: add_ptr_to_bulk_krc_lock kernel/rcu/tree.c:3360 [inline]
 #2: ffff8880b9529470 (krc.lock){....}-{2:2}, at: kvfree_call_rcu+0x192/0x7c0 kernel/rcu/tree.c:3445

stack backtrace:
CPU: 1 PID: 5489 Comm: syz-executor.0 Not tainted 6.8.0-syzkaller-08951-gfe46a7dd189e-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
 __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
 lock_acquire+0x1e4/0x530 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
 lock_hrtimer_base kernel/time/hrtimer.c:175 [inline]
 hrtimer_start_range_ns+0xdf/0xc60 kernel/time/hrtimer.c:1303
 hrtimer_start include/linux/hrtimer.h:275 [inline]
 run_page_cache_worker kernel/rcu/tree.c:3342 [inline]
 kvfree_call_rcu+0x60e/0x7c0 kernel/rcu/tree.c:3447
 trie_update_elem+0x819/0xc10 kernel/bpf/lpm_trie.c:385
 bpf_map_update_value+0x4d3/0x540 kernel/bpf/syscall.c:203
 generic_map_update_batch+0x60d/0x900 kernel/bpf/syscall.c:1876
 bpf_map_do_batch+0x3e0/0x690 kernel/bpf/syscall.c:5145
 __sys_bpf+0x377/0x810
 __do_sys_bpf kernel/bpf/syscall.c:5738 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5736 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5736
 do_syscall_64+0xfb/0x240
 entry_SYSCALL_64_after_hwframe+0x6d/0x75
RIP: 0033:0x7f44a5a7dda9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f44a686a0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007f44a5babf80 RCX: 00007f44a5a7dda9
RDX: 0000000000000038 RSI: 0000000020000000 RDI: 000000000000001a
RBP: 00007f44a5aca47a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f44a5babf80 R15: 00007ffc1ffeb058
 </TASK>


Tested on:

commit:         fe46a7dd Merge tag 'sound-6.9-rc1' of git://git.kernel..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=148dffe6180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fe78468a74fdc3b7
dashboard link: https://syzkaller.appspot.com/bug?extid=1fa663a2100308ab6eab
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=15a5ffe6180000