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

From: syzbot
Date: Sat Mar 30 2024 - 11:34:11 EST

Hello,

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

======================================================
WARNING: possible circular locking dependency detected
6.8.0-syzkaller-08951-gfe46a7dd189e-dirty #0 Not tainted
------------------------------------------------------
syz-executor.0/5491 is trying to acquire lock:
ffff8880b9529470 (#2){..-.}-{2:2}, at: krc_this_cpu_lock kernel/rcu/tree.c:2960 [inline]
ffff8880b9529470 (#2){..-.}-{2:2}, at: add_ptr_to_bulk_krc_lock kernel/rcu/tree.c:3359 [inline]
ffff8880b9529470 (#2){..-.}-{2:2}, at: kvfree_call_rcu+0x18a/0x790 kernel/rcu/tree.c:3444

but task is already holding lock:
ffff88806aa8d9f8 (&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:

-> #2 (&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
bpf_prog_2c29ac5cdc6b1842+0x42/0x46
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

-> #1 (hrtimer_bases.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
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:3341 [inline]
kvfree_call_rcu+0x5e6/0x790 kernel/rcu/tree.c:3446
net_assign_generic net/core/net_namespace.c:115 [inline]
ops_init+0x2c6/0x610 net/core/net_namespace.c:130
__register_pernet_operations net/core/net_namespace.c:1243 [inline]
register_pernet_operations+0x2cb/0x660 net/core/net_namespace.c:1312
register_pernet_device+0x33/0x80 net/core/net_namespace.c:1399
init_mac80211_hwsim+0x12f/0xa90 drivers/net/wireless/virtual/mac80211_hwsim.c:6705
do_one_initcall+0x238/0x830 init/main.c:1241
do_initcall_level+0x157/0x210 init/main.c:1303
do_initcalls+0x3f/0x80 init/main.c:1319
kernel_init_freeable+0x435/0x5d0 init/main.c:1550
kernel_init+0x1d/0x2a0 init/main.c:1439
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243

-> #0 (#2){..-.}-{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 include/linux/spinlock_api_smp.h:133 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
krc_this_cpu_lock kernel/rcu/tree.c:2960 [inline]
add_ptr_to_bulk_krc_lock kernel/rcu/tree.c:3359 [inline]
kvfree_call_rcu+0x18a/0x790 kernel/rcu/tree.c:3444
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:

Chain exists of:
#2 --> hrtimer_bases.lock --> &trie->lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&trie->lock);
lock(hrtimer_bases.lock);
lock(&trie->lock);
lock(#2);

*** DEADLOCK ***

2 locks held by syz-executor.0/5491:
#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: ffff88806aa8d9f8 (&trie->lock){....}-{2:2}, at: trie_update_elem+0xcb/0xc10 kernel/bpf/lpm_trie.c:324

stack backtrace:
CPU: 1 PID: 5491 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 include/linux/spinlock_api_smp.h:133 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
krc_this_cpu_lock kernel/rcu/tree.c:2960 [inline]
add_ptr_to_bulk_krc_lock kernel/rcu/tree.c:3359 [inline]
kvfree_call_rcu+0x18a/0x790 kernel/rcu/tree.c:3444
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: 0033:0x7f4922e7dda9
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:00007f4923b110c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007f4922fabf80 RCX: 00007f4922e7dda9
RDX: 0000000000000038 RSI: 0000000020000000 RDI: 000000000000001a
RBP: 00007f4922eca47a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f4922fabf80 R15: 00007ffdff5b6398
</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=106b0795180000
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=15a8bd41180000