linux-kernel - Re: x86/kprobes: kretprobe fails to triggered if kprobe at function entry is not optimized (trigger by int3 breakpoint)

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Message-ID: <20200825073651.GW1362448@hirez.programming.kicks-ass.net>
Date:   Tue, 25 Aug 2020 09:36:51 +0200
From:   peterz@...radead.org
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     "Eddy_Wu@...ndmicro.com" <Eddy_Wu@...ndmicro.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: x86/kprobes: kretprobe fails to triggered if kprobe at function
 entry is not optimized (trigger by int3 breakpoint)

On Tue, Aug 25, 2020 at 03:15:03AM +0900, Masami Hiramatsu wrote:

> > I did the below, but i'm not at all sure that isn't horrible broken. I
> > can't really find many rp->lock sites and this might break things by
> > limiting contention.
> 
> This is not enough. 

I was afraid of that..

> For checking the recursion of kretprobes, we might
> need kretprobe_table_trylock() or kretprobe_table_busy() (but both
> can be false positive)

Agreed.

> Note that rp->lock shouldn't matter unless we will support recursive
> kprobe itself. (even though, we can use raw_spin_trylock_irqsave())

If the deadlock mentioned isn't about rp->lock, then what it is about?