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Date:   Wed, 9 Sep 2020 14:28:40 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Masami Hiramatsu <mhiramat@kernel.org>
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Subject: Re: [PATCH v5 00/21] kprobes: Unify kretprobe trampoline handlers
 and make kretprobe lockless
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On Wed, 9 Sep 2020 00:09:23 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> > > Of course make it lockless then warning is gone.
> > > But even without the lockless patch, this warning can be false-positive
> > > because we prohibit nested kprobe call, right?
> > 
> > Yes, because the actual nesting is avoided by kprobe_busy, but lockdep
> > can't tell. Lockdep sees a regular lock user and an in-nmi lock user and
> > figures that's a bad combination.

Hmm, what about introducing new LOCK_USED_KPROBE bit, which will be set
if the lock is accessed when the current_kprobe is set (including kprobe_busy)?
This means it is in the kprobe user-handler context. If we access the lock always
in the kprobes context, it is never nested.

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>