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

syzbot
2024-06-05T07:39:04Z

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
--------------------------------------------
udevd/5414 is trying to acquire lock:
ffff88807eff51f8 (&trie->lock){-.-.}-{2:2}, at: trie_delete_elem+0x96/0x6a0 kernel/bpf/lpm_trie.c:462

but task is already holding lock:
ffff88807eff59f8 (&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

5 locks held by udevd/5414:
#0: ffff88801f3e8f08 (kn->active#5){.+.+}-{0:0}, at: kernfs_fop_open+0x93/0xd10 fs/kernfs/file.c:601
#1: ffff8880162ecc38 (&kernfs_locks->open_file_mutex[count]){+.+.}-{3:3}, at: kernfs_open_file_mutex_lock fs/kernfs/file.c:56 [inline]
#1: ffff8880162ecc38 (&kernfs_locks->open_file_mutex[count]){+.+.}-{3:3}, at: kernfs_get_open_node fs/kernfs/file.c:520 [inline]
#1: ffff8880162ecc38 (&kernfs_locks->open_file_mutex[count]){+.+.}-{3:3}, at: kernfs_fop_open+0x74d/0xd10 fs/kernfs/file.c:700
#2: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
#2: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:781 [inline]
#2: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2409 [inline]
#2: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run2+0x21f/0x570 kernel/trace/bpf_trace.c:2451
#3: ffff88807eff59f8 (&trie->lock){-.-.}-{2:2}, at: trie_delete_elem+0x96/0x6a0 kernel/bpf/lpm_trie.c:462
#4: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
#4: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:781 [inline]
#4: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2409 [inline]
#4: ffffffff8e333f60 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run2+0x21f/0x570 kernel/trace/bpf_trace.c:2451

stack backtrace:
CPU: 1 PID: 5414 Comm: udevd 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
kernfs_open_file_mutex_lock fs/kernfs/file.c:56 [inline]
kernfs_get_open_node fs/kernfs/file.c:520 [inline]
kernfs_fop_open+0x74d/0xd10 fs/kernfs/file.c:700
do_dentry_open+0x95a/0x1720 fs/open.c:955
do_open fs/namei.c:3650 [inline]
path_openat+0x289f/0x3280 fs/namei.c:3807
do_filp_open+0x235/0x490 fs/namei.c:3834
do_sys_openat2+0x13e/0x1d0 fs/open.c:1405
do_sys_open fs/open.c:1420 [inline]
__do_sys_openat fs/open.c:1436 [inline]
__se_sys_openat fs/open.c:1431 [inline]
__x64_sys_openat+0x247/0x2a0 fs/open.c:1431
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: 0033:0x7f7f17b169a4
Code: 24 20 48 8d 44 24 30 48 89 44 24 28 64 8b 04 25 18 00 00 00 85 c0 75 2c 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 76 60 48 8b 15 55 a4 0d 00 f7 d8 64 89 02 48 83
RSP: 002b:00007ffdf6fcc1a0 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000000000000008 RCX: 00007f7f17b169a4
RDX: 0000000000080000 RSI: 00007ffdf6fcc2d8 RDI: 00000000ffffff9c
RBP: 00007ffdf6fcc2d8 R08: 0000000000000008 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000080000
R13: 000056111e750b42 R14: 0000000000000001 R15: 000056111e76c160
</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=111a49bc980000
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.