linux-kernel - Re: [PATCH 2/2] bpf: Implement kretprobe fallback for kprobe multi link

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Message-Id: <20251222080046.2312024-1-liujing40@xiaomi.com>
Date: Mon, 22 Dec 2025 16:00:46 +0800
From: liujing40 <liujing.root@...il.com>
To: rostedt@...dmis.org
Cc: alexei.starovoitov@...il.com,
	andrii@...nel.org,
	ast@...nel.org,
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Subject: Re: [PATCH 2/2] bpf: Implement kretprobe fallback for kprobe multi link

On Thu, 18 Dec 2025 16:09:25 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:
> On Thu, 18 Dec 2025 09:53:16 -0800
> Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> 
> > > +static void bpf_kprobe_unregister(struct bpf_kprobe *kps, u32 cnt)
> > > +{
> > > +       for (int i = 0; i < cnt; i++)
> > > +               unregister_kretprobe(&kps[i].rp);
> > > +}  
> > 
> > Nack.
> > This is not a good idea.
> > unregister_kretprobe() calls synchronize_rcu().
> > So the above loop will cause soft lockups for sure.
> 
> Looks like it could be replaced with:
> 
> 	unregister_kretprobes(kps, cnt);
> 
> Which unregisters an array of kreptrobes and does a single
> synchronize_rcu().
> 
> -- Steve

Thanks for the suggestion. I will refactor the loop to use
unregister_kretprobes() for a single RCU sync.