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possible deadlock in htab_lock_bucket

Status: upstream: reported syz repro on 2025/10/28 07:33
Reported-by: syzbot+b41573d719ff7fa9f894@syzkaller.appspotmail.com
First crash: 36d, last: 21d
▶ ▼ Bug presence (1)
Date Name Commit Repro Result
2025/11/13 upstream (ToT) 6fa9041b7177 syz Didn't crash
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in htab_lock_bucket (2) bpf 4 C error error 6 253d 485d 0/29 auto-obsoleted due to no activity on 2025/08/26 22:14
linux-6.1 possible deadlock in htab_lock_bucket origin:upstream missing-backport 4 C inconclusive 11 4d16h 595d 0/3 upstream: reported C repro on 2024/04/17 13:40

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor/5933 is trying to acquire lock:
ffff88807d9fb218 (&htab->lockdep_key#30){-...}-{2:2}, at: htab_lock_bucket+0x181/0x300 kernel/bpf/hashtab.c:166

but task is already holding lock:
ffff8880611a1188 (&htab->lockdep_key#31){-...}-{2:2}, at: htab_lock_bucket+0x181/0x300 kernel/bpf/hashtab.c:166

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&htab->lockdep_key#31){-...}-{2:2}:
       __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
       _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
       htab_lock_bucket+0x181/0x300 kernel/bpf/hashtab.c:166
       htab_lru_map_delete_elem+0x1a4/0x630 kernel/bpf/hashtab.c:1479
       bpf_prog_2c29ac5cdc6b1842+0x42/0x46
       bpf_dispatcher_nop_func include/linux/bpf.h:1224 [inline]
       __bpf_prog_run include/linux/filter.h:612 [inline]
       bpf_prog_run include/linux/filter.h:619 [inline]
       __bpf_trace_run kernel/trace/bpf_trace.c:2322 [inline]
       bpf_trace_run2+0x1d1/0x3c0 kernel/trace/bpf_trace.c:2361
       __bpf_trace_contention_end+0xdd/0x130 include/trace/events/lock.h:122
       __traceiter_contention_end+0x78/0xb0 include/trace/events/lock.h:122
       trace_contention_end+0xe6/0x110 include/trace/events/lock.h:122
       __pv_queued_spin_lock_slowpath+0x7ec/0x9d0 kernel/locking/qspinlock.c:560
       pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:586 [inline]
       queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
       queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
       do_raw_spin_lock+0x24e/0x2c0 kernel/locking/spinlock_debug.c:115
       htab_lock_bucket+0x181/0x300 kernel/bpf/hashtab.c:166
       htab_lru_map_delete_elem+0x1a4/0x630 kernel/bpf/hashtab.c:1479
       bpf_prog_2c29ac5cdc6b1842+0x42/0x46
       bpf_dispatcher_nop_func include/linux/bpf.h:1224 [inline]
       __bpf_prog_run include/linux/filter.h:612 [inline]
       bpf_prog_run include/linux/filter.h:619 [inline]
       __bpf_trace_run kernel/trace/bpf_trace.c:2322 [inline]
       bpf_trace_run2+0x1d1/0x3c0 kernel/trace/bpf_trace.c:2361
       __bpf_trace_contention_end+0xdd/0x130 include/trace/events/lock.h:122
       __traceiter_contention_end+0x78/0xb0 include/trace/events/lock.h:122
       trace_contention_end+0xc5/0xe0 include/trace/events/lock.h:122
       __mutex_lock_common kernel/locking/mutex.c:612 [inline]
       __mutex_lock+0x2fa/0xcc0 kernel/locking/mutex.c:747
       srcu_advance_state kernel/rcu/srcutree.c:1641 [inline]
       process_srcu+0x6d/0x1330 kernel/rcu/srcutree.c:1795
       process_one_work kernel/workqueue.c:2634 [inline]
       process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
       worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
       kthread+0x2fa/0x390 kernel/kthread.c:388
       ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
       ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

-> #0 (&htab->lockdep_key#30){-...}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain kernel/locking/lockdep.c:3869 [inline]
       __lock_acquire+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
       lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
       __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
       _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
       htab_lock_bucket+0x181/0x300 kernel/bpf/hashtab.c:166
       htab_lru_map_delete_elem+0x1a4/0x630 kernel/bpf/hashtab.c:1479
       bpf_prog_2c29ac5cdc6b1842+0x42/0x46
       bpf_dispatcher_nop_func include/linux/bpf.h:1224 [inline]
       __bpf_prog_run include/linux/filter.h:612 [inline]
       bpf_prog_run include/linux/filter.h:619 [inline]
       __bpf_trace_run kernel/trace/bpf_trace.c:2322 [inline]
       bpf_trace_run2+0x1d1/0x3c0 kernel/trace/bpf_trace.c:2361
       __bpf_trace_contention_end+0xdd/0x130 include/trace/events/lock.h:122
       __traceiter_contention_end+0x78/0xb0 include/trace/events/lock.h:122
       trace_contention_end+0xe6/0x110 include/trace/events/lock.h:122
       __pv_queued_spin_lock_slowpath+0x7ec/0x9d0 kernel/locking/qspinlock.c:560
       pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:586 [inline]
       queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
       queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
       do_raw_spin_lock+0x24e/0x2c0 kernel/locking/spinlock_debug.c:115
       htab_lock_bucket+0x181/0x300 kernel/bpf/hashtab.c:166
       htab_lru_map_delete_elem+0x1a4/0x630 kernel/bpf/hashtab.c:1479
       bpf_prog_2c29ac5cdc6b1842+0x42/0x46
       bpf_dispatcher_nop_func include/linux/bpf.h:1224 [inline]
       __bpf_prog_run include/linux/filter.h:612 [inline]
       bpf_prog_run include/linux/filter.h:619 [inline]
       __bpf_trace_run kernel/trace/bpf_trace.c:2322 [inline]
       bpf_trace_run2+0x1d1/0x3c0 kernel/trace/bpf_trace.c:2361
       __bpf_trace_contention_end+0xdd/0x130 include/trace/events/lock.h:122
       __traceiter_contention_end+0x78/0xb0 include/trace/events/lock.h:122
       trace_contention_end+0xc5/0xe0 include/trace/events/lock.h:122
       __mutex_lock_common kernel/locking/mutex.c:612 [inline]
       __mutex_lock+0x2fa/0xcc0 kernel/locking/mutex.c:747
       xt_find_target+0x81/0x230 net/netfilter/x_tables.c:254
       xt_request_find_target+0x5f/0x120 net/netfilter/x_tables.c:282
       find_check_entry net/ipv6/netfilter/ip6_tables.c:563 [inline]
       translate_table+0x16a9/0x2020 net/ipv6/netfilter/ip6_tables.c:733
       do_replace net/ipv6/netfilter/ip6_tables.c:1154 [inline]
       do_ip6t_set_ctl+0x969/0xcd0 net/ipv6/netfilter/ip6_tables.c:1644
       nf_setsockopt+0x263/0x280 net/netfilter/nf_sockopt.c:101
       do_sock_setsockopt+0x175/0x1a0 net/socket.c:2322
       __sys_setsockopt net/socket.c:2345 [inline]
       __do_sys_setsockopt net/socket.c:2354 [inline]
       __se_sys_setsockopt net/socket.c:2351 [inline]
       __x64_sys_setsockopt+0x184/0x200 net/socket.c:2351
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&htab->lockdep_key#31);
                               lock(&htab->lockdep_key#30);
                               lock(&htab->lockdep_key#31);
  lock(&htab->lockdep_key#30);

 *** DEADLOCK ***

4 locks held by syz-executor/5933:
 #0: ffff88814cc00d88 (&xt[i].mutex){+.+.}-{3:3}, at: xt_find_target+0x81/0x230 net/netfilter/x_tables.c:254
 #1: ffffffff8cd2fee0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 #1: ffffffff8cd2fee0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
 #1: ffffffff8cd2fee0 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2321 [inline]
 #1: ffffffff8cd2fee0 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run2+0xde/0x3c0 kernel/trace/bpf_trace.c:2361
 #2: ffff8880611a1188 (&htab->lockdep_key#31){-...}-{2:2}, at: htab_lock_bucket+0x181/0x300 kernel/bpf/hashtab.c:166
 #3: ffffffff8cd2fee0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 #3: ffffffff8cd2fee0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
 #3: ffffffff8cd2fee0 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2321 [inline]
 #3: ffffffff8cd2fee0 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run2+0xde/0x3c0 kernel/trace/bpf_trace.c:2361

stack backtrace:
CPU: 0 PID: 5933 Comm: syz-executor Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
 check_noncircular+0x2bd/0x3c0 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 kernel/locking/lockdep.c:3869 [inline]
 __lock_acquire+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
 lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
 htab_lock_bucket+0x181/0x300 kernel/bpf/hashtab.c:166
 htab_lru_map_delete_elem+0x1a4/0x630 kernel/bpf/hashtab.c:1479
 bpf_prog_2c29ac5cdc6b1842+0x42/0x46
 bpf_dispatcher_nop_func include/linux/bpf.h:1224 [inline]
 __bpf_prog_run include/linux/filter.h:612 [inline]
 bpf_prog_run include/linux/filter.h:619 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2322 [inline]
 bpf_trace_run2+0x1d1/0x3c0 kernel/trace/bpf_trace.c:2361
 __bpf_trace_contention_end+0xdd/0x130 include/trace/events/lock.h:122
 __traceiter_contention_end+0x78/0xb0 include/trace/events/lock.h:122
 trace_contention_end+0xe6/0x110 include/trace/events/lock.h:122
 __pv_queued_spin_lock_slowpath+0x7ec/0x9d0 kernel/locking/qspinlock.c:560
 pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:586 [inline]
 queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
 queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
 do_raw_spin_lock+0x24e/0x2c0 kernel/locking/spinlock_debug.c:115
 htab_lock_bucket+0x181/0x300 kernel/bpf/hashtab.c:166
 htab_lru_map_delete_elem+0x1a4/0x630 kernel/bpf/hashtab.c:1479
 bpf_prog_2c29ac5cdc6b1842+0x42/0x46
 bpf_dispatcher_nop_func include/linux/bpf.h:1224 [inline]
 __bpf_prog_run include/linux/filter.h:612 [inline]
 bpf_prog_run include/linux/filter.h:619 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2322 [inline]
 bpf_trace_run2+0x1d1/0x3c0 kernel/trace/bpf_trace.c:2361
 __bpf_trace_contention_end+0xdd/0x130 include/trace/events/lock.h:122
 __traceiter_contention_end+0x78/0xb0 include/trace/events/lock.h:122
 trace_contention_end+0xc5/0xe0 include/trace/events/lock.h:122
 __mutex_lock_common kernel/locking/mutex.c:612 [inline]
 __mutex_lock+0x2fa/0xcc0 kernel/locking/mutex.c:747
 xt_find_target+0x81/0x230 net/netfilter/x_tables.c:254
 xt_request_find_target+0x5f/0x120 net/netfilter/x_tables.c:282
 find_check_entry net/ipv6/netfilter/ip6_tables.c:563 [inline]
 translate_table+0x16a9/0x2020 net/ipv6/netfilter/ip6_tables.c:733
 do_replace net/ipv6/netfilter/ip6_tables.c:1154 [inline]
 do_ip6t_set_ctl+0x969/0xcd0 net/ipv6/netfilter/ip6_tables.c:1644
 nf_setsockopt+0x263/0x280 net/netfilter/nf_sockopt.c:101
 do_sock_setsockopt+0x175/0x1a0 net/socket.c:2322
 __sys_setsockopt net/socket.c:2345 [inline]
 __do_sys_setsockopt net/socket.c:2354 [inline]
 __se_sys_setsockopt net/socket.c:2351 [inline]
 __x64_sys_setsockopt+0x184/0x200 net/socket.c:2351
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f6d0b7915ba
Code: ff ff ff c3 0f 1f 40 00 48 c7 c2 a8 ff ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 49 89 ca b8 36 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 06 c3 0f 1f 44 00 00 48 c7 c2 a8 ff ff ff f7
RSP: 002b:00007ffc3f9b8118 EFLAGS: 00000206 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007ffc3f9b81a0 RCX: 00007f6d0b7915ba
RDX: 0000000000000040 RSI: 0000000000000029 RDI: 0000000000000003
RBP: 0000000000000003 R08: 00000000000003b8 R09: 0079746972756365
R10: 00007f6d0b9b2d00 R11: 0000000000000206 R12: 00007f6d0b9b2ca0
R13: 00007ffc3f9b813c R14: 0000000000000000 R15: 00007f6d0b9b4e60
 </TASK>

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/11/13 00:11 linux-6.6.y 0a805b6ea8cd 07e030de .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf possible deadlock in htab_lock_bucket
2025/11/12 21:53 linux-6.6.y 0a805b6ea8cd 07e030de .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf possible deadlock in htab_lock_bucket
2025/11/10 23:26 linux-6.6.y 0a805b6ea8cd 4e1406b4 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf possible deadlock in htab_lock_bucket
2025/11/10 20:55 linux-6.6.y 0a805b6ea8cd 4e1406b4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf possible deadlock in htab_lock_bucket
2025/10/28 07:33 linux-6.6.y 4a243110dc88 fd2207e7 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf possible deadlock in htab_lock_bucket
* Struck through repros no longer work on HEAD.