[syzbot] [net?] [fs?] possible deadlock in rht_lock

[syzbot] [net?] [fs?] possible deadlock in rht_lock

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    94515f3a7d42 Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=119bf789580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5c4196ba0e33631d
dashboard link: https://syzkaller.appspot.com/bug?extid=ef8d17bae14efb960935
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=148d72b9580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=105a1746580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f43aa5dbbaea/disk-94515f3a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d34e80893dbb/vmlinux-94515f3a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/62b4a6d766f6/bzImage-94515f3a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ef8d17bae14efb960935@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz-executor/5768 is trying to acquire lock:
ffff88807d7f7038 (rhashtable_bucket){-.-.}-{0:0}, at: rht_lock+0x8b/0x180 include/linux/rhashtable.h:331

but task is already holding lock:
ffff88802cc48038 (rhashtable_bucket){-.-.}-{0:0}, at: rht_lock+0x8b/0x180 include/linux/rhashtable.h:331

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

       CPU0
       ----
  lock(rhashtable_bucket);
  lock(rhashtable_bucket);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

5 locks held by syz-executor/5768:
 #0: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #0: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #0: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: __rhashtable_insert_fast include/linux/rhashtable.h:774 [inline]
 #0: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rhashtable_insert_fast include/linux/rhashtable.h:887 [inline]
 #0: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: pidfs_add_pid+0x169/0xc50 fs/pidfs.c:178
 #1: ffff88802cc48038 (rhashtable_bucket){-.-.}-{0:0}, at: rht_lock+0x8b/0x180 include/linux/rhashtable.h:331
 #2: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #2: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #2: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: trace_call_bpf+0xb6/0xb80 kernel/trace/bpf_trace.c:-1
 #3: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #3: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #3: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: class_rcu_constructor include/linux/rcupdate.h:1183 [inline]
 #3: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rhtab_map_delete_elem+0x21/0x190 kernel/bpf/hashtab.c:2979
 #4: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #4: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #4: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: __rhashtable_remove_fast include/linux/rhashtable.h:1137 [inline]
 #4: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rhashtable_remove_fast include/linux/rhashtable.h:1175 [inline]
 #4: ffffffff8eb59c60 (rcu_read_lock){....}-{1:3}, at: rhtab_delete_elem+0x15c/0x1b30 kernel/bpf/hashtab.c:-1

stack backtrace:
CPU: 1 UID: 0 PID: 5768 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain kernel/locking/lockdep.c:3895 [inline]
 __lock_acquire+0x24df/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 rht_lock+0xa3/0x180 include/linux/rhashtable.h:331
 __rhashtable_remove_fast_one include/linux/rhashtable.h:1065 [inline]
 __rhashtable_remove_fast include/linux/rhashtable.h:1146 [inline]
 rhashtable_remove_fast include/linux/rhashtable.h:1175 [inline]
 rhtab_delete_elem+0x404/0x1b30 kernel/bpf/hashtab.c:2954
 rhtab_map_delete_elem+0xe2/0x190 kernel/bpf/hashtab.c:2985
 bpf_prog_a4f1e23443ac9f8e+0x4e/0x56
 bpf_dispatcher_nop_func include/linux/bpf.h:1454 [inline]
 __bpf_prog_run include/linux/filter.h:724 [inline]
 bpf_prog_run include/linux/filter.h:731 [inline]
 bpf_prog_run_array include/linux/bpf.h:2597 [inline]
 trace_call_bpf+0x3f0/0xb80 kernel/trace/bpf_trace.c:147
 perf_trace_run_bpf_submit+0x78/0x170 kernel/events/core.c:11398
 do_perf_trace_lock include/trace/events/lock.h:49 [inline]
 perf_trace_lock+0x32d/0x410 include/trace/events/lock.h:49
 __do_trace_lock_release include/trace/events/lock.h:68 [inline]
 trace_lock_release include/trace/events/lock.h:68 [inline]
 lock_release+0x38e/0x3c0 kernel/locking/lockdep.c:5879
 rht_assign_unlock include/linux/rhashtable.h:431 [inline]
 __rhashtable_insert_fast include/linux/rhashtable.h:850 [inline]
 rhashtable_insert_fast include/linux/rhashtable.h:887 [inline]
 pidfs_add_pid+0x650/0xc50 fs/pidfs.c:178
 alloc_pid+0xe7a/0x1310 kernel/pid.c:338
 copy_process+0x20ea/0x4390 kernel/fork.c:2305
 kernel_clone+0x2d7/0x940 kernel/fork.c:2748
 __do_sys_clone kernel/fork.c:2889 [inline]
 __se_sys_clone kernel/fork.c:2873 [inline]
 __x64_sys_clone+0x1b6/0x230 kernel/fork.c:2873
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f703d7c6912
Code: 89 e7 e8 71 8b f7 ff 45 31 c0 31 d2 31 f6 64 48 8b 04 25 10 00 00 00 bf 11 00 20 01 4c 8d 90 d0 02 00 00 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 66 89 c5 85 c0 75 3b 64 48 8b 04 25 10 00 00
RSP: 002b:00007ffe5db74e40 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007ffe5db74e40 RCX: 00007f703d7c6912
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
RBP: 00007ffe5db74fcc R08: 0000000000000000 R09: 0000000000000000
R10: 000055556f65e7d0 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000000927c0 R14: 0000000000025e7d R15: 00007ffe5db75020
 </TASK>


---
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