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Date:   Fri, 1 May 2020 11:01:07 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ingo Molnar <mingo@...e.hu>, Ingo Molnar <mingo@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, 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: [PATCHv2] kretprobe: Prevent triggering kretprobe from within
 kprobe_flush_task

On Tue, 28 Apr 2020 23:36:27 +0200
Jiri Olsa <jolsa@...hat.com> wrote:

> On Fri, Apr 17, 2020 at 04:38:10PM +0900, Masami Hiramatsu wrote:
> 
> SNIP
> 
> > > 
> > > The code within the kretprobe handler checks for probe reentrancy,
> > > so we won't trigger any _raw_spin_lock_irqsave probe in there.
> > > 
> > > The problem is in outside kprobe_flush_task, where we call:
> > > 
> > >   kprobe_flush_task
> > >     kretprobe_table_lock
> > >       raw_spin_lock_irqsave
> > >         _raw_spin_lock_irqsave
> > > 
> > > where _raw_spin_lock_irqsave triggers the kretprobe and installs
> > > kretprobe_trampoline handler on _raw_spin_lock_irqsave return.
> > > 
> > > The kretprobe_trampoline handler is then executed with already
> > > locked kretprobe_table_locks, and first thing it does is to
> > > lock kretprobe_table_locks ;-) the whole lockup path like:
> > > 
> > >   kprobe_flush_task
> > >     kretprobe_table_lock
> > >       raw_spin_lock_irqsave
> > >         _raw_spin_lock_irqsave ---> probe triggered, kretprobe_trampoline installed
> > > 
> > >         ---> kretprobe_table_locks locked
> > > 
> > >         kretprobe_trampoline
> > >           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.
> > > 
> > 
> > Thanks Jiri!
> > 
> > Ingo, could you pick this up?
> 
> Ingo, any chance you could take this one?

Hi Ingo,

Should I make a pull request for all kprobes related patches to you?

Thank you,

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

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