linux-kernel - Re: [PATCH] kretprobe: Prevent triggering kretprobe from within kprobe_flush

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Date:   Thu, 16 Apr 2020 22:42:50 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Peter Zijlstra <peterz@...radead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "bibo,mao" <bibo.mao@...el.com>,
        "Ziqian SUN (Zamir)" <zsun@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH] kretprobe: Prevent triggering kretprobe from within
 kprobe_flush_task

Hi Jiri,

On Thu, 16 Apr 2020 11:13:20 +0200
Jiri Olsa <jolsa@...hat.com> wrote:

> On Thu, Apr 16, 2020 at 10:55:06AM +0900, Masami Hiramatsu wrote:
> 
> SNIP
> 
> > >           trampoline_handler
> > >             kretprobe_hash_lock(current, &head, &flags);  <--- deadlock
> > > 
> > > Adding kprobe_busy_begin/end helpers that mark code with fake
> > > probe installed to prevent triggering of another kprobe within
> > > this code.
> > > 
> > > Using these helpers in kprobe_flush_task, so the probe recursion
> > > protection check is hit and the probe is never set to prevent
> > > above lockup.
> > > 
> > > Reported-by: "Ziqian SUN (Zamir)" <zsun@...hat.com>
> > > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > 
> > Thanks Jiri and Ziqian!
> > 
> > Looks good to me.
> > 
> > Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
> > 
> > BTW, this is a kind of bugfix. So should it add a Fixes tag?
> > 
> > Fixes: ef53d9c5e4da ('kprobes: improve kretprobe scalability with hashed locking')
> > Cc: stable@...r.kernel.org
> 
> ah right, do you want me to repost with those?

Yeah, if you don't mind.

Thank you,

> 
> thanks,
> jirka
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>