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Date:   Thu, 16 Apr 2020 11:13:20 +0200
From:   Jiri Olsa <jolsa@redhat.com>
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Jiri Olsa <jolsa@kernel.org>,
        "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
        "David S. Miller" <davem@davemloft.net>,
        Peter Zijlstra <peterz@infradead.org>,
        lkml <linux-kernel@vger.kernel.org>,
        "bibo,mao" <bibo.mao@intel.com>,
        "Ziqian SUN (Zamir)" <zsun@redhat.com>, stable@vger.kernel.org
Subject: Re: [PATCH] kretprobe: Prevent triggering kretprobe from within
 kprobe_flush_task
Message-ID: <20200416091320.GA322899@krava>
References: <20200408164641.3299633-1-jolsa@kernel.org>
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 <20200409184451.GG3309111@krava>
 <20200409201336.GH3309111@krava>
 <20200410093159.0d7000a08fd76c2eaf1398f8@kernel.org>
 <20200414160338.GE208694@krava>
 <20200415090507.GG208694@krava>
 <20200416105506.904b7847a1b621b75463076d@kernel.org>
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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@redhat.com>
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> 
> Thanks Jiri and Ziqian!
> 
> Looks good to me.
> 
> Acked-by: Masami Hiramatsu <mhiramat@kernel.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@vger.kernel.org

ah right, do you want me to repost with those?

thanks,
jirka