linux-kernel - [syzbot] [bpf?] possible deadlock in bpf_lru_push

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Message-ID: <69155df5.a70a0220.3124cb.0018.GAE@google.com>
Date: Wed, 12 Nov 2025 20:26:29 -0800
From: syzbot <syzbot+18b26edb69b2e19f3b33@...kaller.appspotmail.com>
To: andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org, 
	daniel@...earbox.net, eddyz87@...il.com, haoluo@...gle.com, 
	john.fastabend@...il.com, jolsa@...nel.org, kpsingh@...nel.org, 
	linux-kernel@...r.kernel.org, martin.lau@...ux.dev, netdev@...r.kernel.org, 
	sdf@...ichev.me, song@...nel.org, syzkaller-bugs@...glegroups.com, 
	yonghong.song@...ux.dev
Subject: [syzbot] [bpf?] possible deadlock in bpf_lru_push_free (2)

Hello,

syzbot found the following issue on:

HEAD commit:    e427054ae7bc Merge branch 'x86-fgraph-bpf-fix-orc-stack-un..
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=136b70b4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e46b8a1c645465a9
dashboard link: https://syzkaller.appspot.com/bug?extid=18b26edb69b2e19f3b33
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10013c12580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16541c12580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c1ac942fc5fb/disk-e427054a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/be05ef12ba31/vmlinux-e427054a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c75604292a15/bzImage-e427054a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+18b26edb69b2e19f3b33@...kaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz-executor149/10558 is trying to acquire lock:
ffffe8ffffc41588 (&loc_l->lock){....}-{2:2}, at: bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:514 [inline]
ffffe8ffffc41588 (&loc_l->lock){....}-{2:2}, at: bpf_lru_push_free+0x33b/0xbb0 kernel/bpf/bpf_lru_list.c:553

but task is already holding lock:
ffffe8ffffc41588 (&loc_l->lock){....}-{2:2}, at: bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:440 [inline]
ffffe8ffffc41588 (&loc_l->lock){....}-{2:2}, at: bpf_lru_pop_free+0x1ab/0x19b0 kernel/bpf/bpf_lru_list.c:496

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

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

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by syz-executor149/10558:
 #0: ffffffff8df3d620 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8df3d620 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #0: ffffffff8df3d620 (rcu_read_lock){....}-{1:3}, at: bpf_percpu_hash_update+0x2b/0x200 kernel/bpf/hashtab.c:2409
 #1: ffffe8ffffc41588 (&loc_l->lock){....}-{2:2}, at: bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:440 [inline]
 #1: ffffe8ffffc41588 (&loc_l->lock){....}-{2:2}, at: bpf_lru_pop_free+0x1ab/0x19b0 kernel/bpf/bpf_lru_list.c:496
 #2: ffffffff8df3d620 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #2: ffffffff8df3d620 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #2: ffffffff8df3d620 (rcu_read_lock){....}-{1:3}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2074 [inline]
 #2: ffffffff8df3d620 (rcu_read_lock){....}-{1:3}, at: bpf_trace_run2+0x186/0x4b0 kernel/trace/bpf_trace.c:2116

stack backtrace:


---
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