linux-kernel - Re: [PATCH -tip V2 0/2] kprobes: Fix RCU warning and cleanup

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Message-ID: <20200110211438.GE128013@google.com>
Date:   Fri, 10 Jan 2020 16:14:38 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Anders Roxell <anders.roxell@...aro.org>, paulmck@...nel.org,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        David Miller <davem@...emloft.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip V2 0/2] kprobes: Fix RCU warning and cleanup

On Tue, Jan 07, 2020 at 09:15:35PM +0900, Masami Hiramatsu wrote:
> Hello,
> 
> Anyone have any comment on this series?
> Without this series, I still see the suspicious RCU warning for kprobe on -tip tree.

+Paul since RCU.

Hi Masami,

I believe I had commented before that I don't agree with this patch:
https://lore.kernel.org/lkml/157535318870.16485.6366477974356032624.stgit@devnote2/

The rationale you used is to replace RCU-api with non-RCU api just to avoid
warnings. I think a better approach is to use RCU api and pass the optional
expression to silence the false-positive warnings by informing the RCU API
about the fact that locks are held (similar to what we do for
rcu_dereference_protected()). The RCU API will do additional checking
(such as making sure preemption is disabled for safe RCU usage etc) as well.

Could you repost the latest versions?

thanks,

 - Joel


> 
> Thank you,
> 
> On Sat, 21 Dec 2019 03:55:41 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > Hi Ingo,
> > 
> > Could you pick this series to fix the false-positive RCU-list warnings?
> > 
> > Thank you,
> > 
> > On Tue,  3 Dec 2019 15:06:06 +0900
> > Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > 
> > > Hi,
> > > 
> > > Here is a couple of patches which fix suspicious RCU
> > > usage warnings in kprobes.
> > > 
> > > Anders reported the first warning in kprobe smoke test
> > > with CONFIG_PROVE_RCU_LIST=y. While fixing this issue,
> > > I found similar issues and cleanups in kprobes.
> > > 
> > > Thank you,
> > > 
> > > ---
> > > 
> > > Masami Hiramatsu (2):
> > >       kprobes: Suppress the suspicious RCU warning on kprobes
> > >       kprobes: Use non RCU traversal APIs on kprobe_tables if possible
> > > 
> > > 
> > >  kernel/kprobes.c |   32 ++++++++++++++++++++++----------
> > >  1 file changed, 22 insertions(+), 10 deletions(-)
> > > 
> > > --
> > > Masami Hiramatsu (Linaro) <mhiramat@...nel.org>
> > 
> > 
> > -- 
> > Masami Hiramatsu <mhiramat@...nel.org>
> 
> 
> -- 
> Masami Hiramatsu <mhiramat@...nel.org>