linux-kernel - Re: [PATCH v5 00/21] kprobes: Unify kretprobe trampoline handlers and make kretprobe lockless

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Message-Id: <20200908115527.cf8d2b106bf1a9c4416bbc89@kernel.org>
Date:   Tue, 8 Sep 2020 11:55:27 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     fche@...hat.com (Frank Ch. Eigler)
Cc:     peterz@...radead.org, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org, Eddy_Wu@...ndmicro.com,
        x86@...nel.org, davem@...emloft.net, rostedt@...dmis.org,
        naveen.n.rao@...ux.ibm.com, anil.s.keshavamurthy@...el.com,
        linux-arch@...r.kernel.org, cameron@...dycamel.com,
        oleg@...hat.com, will@...nel.org, paulmck@...nel.org,
        systemtap@...rceware.org
Subject: Re: [PATCH v5 00/21] kprobes: Unify kretprobe trampoline handlers
 and make kretprobe lockless

On Mon, 07 Sep 2020 13:44:19 -0400
fche@...hat.com (Frank Ch. Eigler) wrote:

> Masami Hiramatsu <mhiramat@...nel.org> writes:
> 
> > Sorry, for noticing this point, I Cc'd to systemtap. Is systemtap taking
> > care of spinlock too?
> 
> On PRREMPT_RT configurations, systemtap uses the raw_spinlock_t
> types/functions, to keep its probe handlers as atomic as we can make them.

OK, if the lock is only used in the probe handlers, there should be
no problem. Even if a probe hits in the NMI which happens in another
kprobe handler, the probe does not call its handler (because we don't
support nested kprobes* yet).
But maybe you'll get warnings if you enable the lockdep.

* https://lkml.kernel.org/r/158894789510.14896.13461271606820304664.stgit@devnote2
It seems that we need more work for the nested kprobes.

Thank you,

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