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Message-ID: <20140508091758.5be6f380@gandalf.local.home>
Date: Thu, 8 May 2014 09:17:58 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Rusty Russell <rusty@...tcorp.com.au>,
Romain Izard <romain.izard.pro@...il.com>,
stable <stable@...r.kernel.org>
Subject: Re: [GIT PULL] trace: module: Maintain a valid user count
Linus,
You can hold off on pulling this if you want. I just received a patch
that fixes a "use after free" bug that was introduced in this merge
window. I've added that patch after this commit, and I'm starting my
tests now. I should have another pull request later today if all goes
well.
-- Steve
On Thu, 8 May 2014 07:13:27 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:
>
> Linus,
>
> This is a long standing bug that causes bogus data to show up
> in the refcnt field of the module_refcnt tracepoint. It was
> introduced by a merge conflict resolution back in 2.6.35-rc days.
>
> The result should be refcnt = incs - decs, but instead it did
> refcnt = incs + decs.
>
> Please pull the latest trace-fixes-v3.15-rc4 tree, which can be found at:
>
>
> git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
> trace-fixes-v3.15-rc4
>
> Tag SHA1: df839af2f97c5761d24b7a1c80f5ac8c4fa63dfe
> Head SHA1: 098507ae3ec2331476fb52e85d4040c1cc6d0ef4
>
>
> Romain Izard (1):
> trace: module: Maintain a valid user count
>
> ----
> include/trace/events/module.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> ---------------------------
> commit 098507ae3ec2331476fb52e85d4040c1cc6d0ef4
> Author: Romain Izard <romain.izard.pro@...il.com>
> Date: Tue Mar 4 10:09:39 2014 +0100
>
> trace: module: Maintain a valid user count
>
> The replacement of the 'count' variable by two variables 'incs' and
> 'decs' to resolve some race conditions during module unloading was done
> in parallel with some cleanup in the trace subsystem, and was integrated
> as a merge.
>
> Unfortunately, the formula for this replacement was wrong in the tracing
> code, and the refcount in the traces was not usable as a result.
>
> Use 'count = incs - decs' to compute the user count.
>
> Link: http://lkml.kernel.org/p/1393924179-9147-1-git-send-email-romain.izard.pro@gmail.com
>
> Acked-by: Ingo Molnar <mingo@...nel.org>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: stable@...r.kernel.org # 2.6.35
> Fixes: c1ab9cab7509 "merge conflict resolution"
> Signed-off-by: Romain Izard <romain.izard.pro@...il.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
>
> diff --git a/include/trace/events/module.h b/include/trace/events/module.h
> index 11fd51b..daa60c7 100644
> --- a/include/trace/events/module.h
> +++ b/include/trace/events/module.h
> @@ -80,7 +80,7 @@ DECLARE_EVENT_CLASS(module_refcnt,
>
> TP_fast_assign(
> __entry->ip = ip;
> - __entry->refcnt = __this_cpu_read(mod->refptr->incs) + __this_cpu_read(mod->refptr->decs);
> + __entry->refcnt = __this_cpu_read(mod->refptr->incs) - __this_cpu_read(mod->refptr->decs);
> __assign_str(name, mod->name);
> ),
>
--
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