linux-kernel - Re: [PATCH 0/2] tracing/tlb/x85: Fix splat of calling RCU trace code on offline CPU

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Message-ID: <CA+icZUVvnOA9O0GMDangTLATPOHU=Do5Kj-fo0bVu5Wfb0TT7Q@mail.gmail.com>
Date:	Fri, 6 Feb 2015 22:07:56 +0100
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Dave Hansen <dave@...1.net>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-next <linux-next@...r.kernel.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Kristen Carlson Accardi <kristen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/2] tracing/tlb/x85: Fix splat of calling RCU trace code
 on offline CPU

On Fri, Feb 6, 2015 at 9:06 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> Paul,
>
> I found a much better fix than adding the rcu_nocheck(). Simply have the
> rcu check inside the condition check as well. This way the rcu splat
> will only happen if the condition is set too. The condition doesn't need
> the tracepoint enabled.
>
> Now I'm thinking that I should push the first patch through my tree as it
> only touches tracing. The second patch you can freely take.
>
> Neither patch really depends on the other, but both patches are required
> to make the splat go away. If Sedat could test these patches together,
> and give his tested-by tag, that would be great. I'll run my patch through
> my full series of tests and then push to linux next. You could take the second
> patch and push that through your tree (linux-next). When both arrive, the
> bug will be fixed. The two do not need to come in together.
>
> Thoughts?
>
> -- Steve
>
>
> Steven Rostedt (Red Hat) (2):
>       tracing: Add condition check to RCU lockdep checks
>       x86/tbl/trace: Do not trace on CPU that is offline
>
> ----
>  include/linux/tracepoint.h | 2 +-
>  include/trace/events/tlb.h | 4 +++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
>

Your patchset fixes the issue for me (look at the attached files for
more detailed information).

I tested the "To Be Loved" (TBL VS. TLB flushes) edition against
Linux-next (next-20150204) where I had originally seen and reported
the call-trace.

Before I forget... The Fixes-tag misses pointing to Dave Hansen's...

commit d17d8f9dedb9dd76fd540a5c497101529d9eb25a
"x86/mm: Add tracepoints for TLB flushes"

My POV is that both patches somehow belong together.
If you decide to push them through two different trees, please add a
note/reference to each other.

Thanks to all involved people nailing this down.

- Sedat -

View attachment "dmesg_3.19.0-rc7-next-20150204.12-iniza-small_for-rostedt-20150206.txt" of type "text/plain" (63867 bytes)

View attachment "3.19.0-rc7-next-20150204.12-iniza-small.patch" of type "text/x-diff" (3232 bytes)

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