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

syzbot
2024-06-05T07:57:05Z

Hello,

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

============================================
WARNING: possible recursive locking detected
6.10.0-rc2-syzkaller-00001-ge377d803b65e #0 Not tainted
--------------------------------------------
syz-executor.0/6233 is trying to acquire lock:
ffff88802e83a1f8 (&trie->lock){-.-.}-{2:2}, at: trie_delete_elem+0x96/0x6a0 kernel/bpf/lpm_trie.c:462

but task is already holding lock:
ffff8880696e91f8 (&trie->lock){-.-.}-{2:2}, at: trie_delete_elem+0x96/0x6a0 kernel/bpf/lpm_trie.c:462

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&trie->lock);
lock(&trie->lock);

*** DEADLOCK ***

May be due to missing lock nesting notation

4 locks held by syz-executor.0/6233:
#0: ffffffff8e3809a8 (tracepoints_mutex){+.+.}-{3:3}, at: tracepoint_probe_unregister+0x32/0x990 kernel/tracepoint.c:548
#1: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
#1: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:781 [inline]
#1: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2409 [inline]
#1: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run2+0x21f/0x570 kernel/trace/bpf_trace.c:2451
#2: ffff8880696e91f8 (&trie->lock){-.-.}-{2:2}, at: trie_delete_elem+0x96/0x6a0 kernel/bpf/lpm_trie.c:462
#3: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
#3: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:781 [inline]
#3: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2409 [inline]
#3: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run2+0x21f/0x570 kernel/trace/bpf_trace.c:2451

stack backtrace:
CPU: 0 PID: 6233 Comm: syz-executor.0 Not tainted 6.10.0-rc2-syzkaller-00001-ge377d803b65e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
check_deadlock kernel/locking/lockdep.c:3062 [inline]
validate_chain+0x15d3/0x5900 kernel/locking/lockdep.c:3856
__lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1ed/0x550 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:462
bpf_prog_1db1603a7cfa36fb+0x45/0x49
bpf_dispatcher_nop_func include/linux/bpf.h:1243 [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:2410 [inline]
bpf_trace_run2+0x30d/0x570 kernel/trace/bpf_trace.c:2451
__traceiter_contention_end+0x7b/0xb0 include/trace/events/lock.h:122
trace_contention_end+0x114/0x140 include/trace/events/lock.h:122
__pv_queued_spin_lock_slowpath+0xb81/0xdc0 kernel/locking/qspinlock.c:557
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+0x272/0x370 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
trie_delete_elem+0x96/0x6a0 kernel/bpf/lpm_trie.c:462
bpf_prog_1db1603a7cfa36fb+0x45/0x49
bpf_dispatcher_nop_func include/linux/bpf.h:1243 [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:2410 [inline]
bpf_trace_run2+0x30d/0x570 kernel/trace/bpf_trace.c:2451
__traceiter_contention_end+0x7b/0xb0 include/trace/events/lock.h:122
trace_contention_end+0xf5/0x120 include/trace/events/lock.h:122
__mutex_lock_common kernel/locking/mutex.c:617 [inline]
__mutex_lock+0x2e5/0xd70 kernel/locking/mutex.c:752
tracepoint_probe_unregister+0x32/0x990 kernel/tracepoint.c:548
bpf_raw_tp_link_release+0x45/0x70 kernel/bpf/syscall.c:3519
bpf_link_free+0x10e/0x2d0 kernel/bpf/syscall.c:3065
bpf_link_put_direct kernel/bpf/syscall.c:3106 [inline]
bpf_link_release+0x7b/0x90 kernel/bpf/syscall.c:3113
__fput+0x406/0x8b0 fs/file_table.c:422
__do_sys_close fs/open.c:1555 [inline]
__se_sys_close fs/open.c:1540 [inline]
__x64_sys_close+0x7f/0x110 fs/open.c:1540
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: 0033:0x7f7ed1e7cb9a
Code: 48 3d 00 f0 ff ff 77 48 c3 0f 1f 80 00 00 00 00 48 83 ec 18 89 7c 24 0c e8 03 7f 02 00 8b 7c 24 0c 89 c2 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 36 89 d7 89 44 24 0c e8 63 7f 02 00 8b 44 24
RSP: 002b:00007ffead8b0970 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 0000000000000007 RCX: 00007f7ed1e7cb9a
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000006
RBP: 00007ffead8b0a48 R08: 00007f7ed1e00000 R09: 0000000000000001
R10: 0000000000000001 R11: 0000000000000293 R12: 000000000001abb1
R13: 00007f7ed1fabf8c R14: 00007f7ed1fabf80 R15: 0000000000000226
</TASK>

Tested on:

commit: e377d803 kernel/trace: fix possible deadlock in trie_d..
git tree: https://linux.googlesource.com/linux/kernel/git/torvalds/linux
console output: https://syzkaller.appspot.com/x/log.txt?x=12178036980000
kernel config: https://syzkaller.appspot.com/x/.config?x=eb72437243175f22
dashboard link: https://syzkaller.appspot.com/bug?extid=9d95beb2a3c260622518
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.