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Subject: Re: [syzbot] [bpf?] WARNING in bpf_bprintf_prepare (3)
Author: listout@listout.xyz

On 20.10.2025 14:08, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    a1e83d4c0361 selftests/bpf: Fix redefinition of 'off' as d..
> git tree:       bpf
> console output: https://syzkaller.appspot.com/x/log.txt?x=12d21de2580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=9ad7b090a18654a7
> dashboard link: https://syzkaller.appspot.com/bug?extid=b0cff308140f79a9c4cb
> 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=160cf542580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=128d5c58580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/2f6a7a0cd1b7/disk-a1e83d4c.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/873984cfc71e/vmlinux-a1e83d4c.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/16711d84070c/bzImage-a1e83d4c.xz
> 
> The issue was bisected to:
> 
> commit 7c33e97a6ef5d84e98b892c3e00c6d1678d20395
> Author: Sahil Chandna <chandna.sahil@gmail.com>
> Date:   Tue Oct 14 18:56:35 2025 +0000
> 
>     bpf: Do not disable preemption in bpf_test_run().
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=172fe492580000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=14afe492580000
> console output: https://syzkaller.appspot.com/x/log.txt?x=10afe492580000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b0cff308140f79a9c4cb@syzkaller.appspotmail.com
> Fixes: 7c33e97a6ef5 ("bpf: Do not disable preemption in bpf_test_run().")

#syz test

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 8b7d0b90fea7..cc4288f408f2 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -36,7 +36,8 @@ struct bpf_test_timer {
 static void bpf_test_timer_enter(struct bpf_test_timer *t)
 	__acquires(rcu)
 {
-	rcu_read_lock_dont_migrate();
+	rcu_read_lock();
+	migrate_disable();
 	t->time_start = ktime_get_ns();
 }
 
@@ -44,7 +45,8 @@ static void bpf_test_timer_leave(struct bpf_test_timer *t)
 	__releases(rcu)
 {
 	t->time_start = 0;
-	rcu_read_unlock_migrate();
+	migrate_enable();
+	rcu_read_unlock();
 }
 
 static bool bpf_test_timer_continue(struct bpf_test_timer *t, int iterations,

-- 
Regards,
listout