From: Amol Grover <frextrite@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
"Paul E . McKenney" <paulmck@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
linux-kernel-mentees@lists.linuxfoundation.org,
linux-kernel@vger.kernel.org,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
Joel Fernandes <joel@joelfernandes.org>,
Namhyung Kim <namhyung@kernel.org>, Jiri Olsa <jolsa@redhat.com>
Subject: Re: [Linux-kernel-mentees] [PATCH] events: Annotate parent_ctx with __rcu
Date: Mon, 10 Feb 2020 18:29:48 +0530 [thread overview]
Message-ID: <20200210125948.GA16485@workstation-portable> (raw)
In-Reply-To: <20200210093624.GB14879@hirez.programming.kicks-ass.net>
On Mon, Feb 10, 2020 at 10:36:24AM +0100, Peter Zijlstra wrote:
> On Sat, Feb 08, 2020 at 08:16:49PM +0530, Amol Grover wrote:
> > parent_ctx is used under RCU context in kernel/events/core.c,
> > tell sparse about it aswell.
> >
> > Fixes the following instances of sparse error:
> > kernel/events/core.c:3221:18: error: incompatible types in comparison
> > kernel/events/core.c:3222:23: error: incompatible types in comparison
> >
> > This introduces the following two sparse errors:
> > kernel/events/core.c:3117:18: error: incompatible types in comparison
> > kernel/events/core.c:3121:30: error: incompatible types in comparison
> >
> > Hence, use rcu_dereference() to access parent_ctx and silence
> > the newly introduced errors.
> >
> > Signed-off-by: Amol Grover <frextrite@gmail.com>
> > ---
> > include/linux/perf_event.h | 2 +-
> > kernel/events/core.c | 11 ++++++++---
> > 2 files changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index 6d4c22aee384..e18a7bdc6f98 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -810,7 +810,7 @@ struct perf_event_context {
> > * These fields let us detect when two contexts have both
> > * been cloned (inherited) from a common ancestor.
> > */
> > - struct perf_event_context *parent_ctx;
> > + struct perf_event_context __rcu *parent_ctx;
> > u64 parent_gen;
> > u64 generation;
> > int pin_count;
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 2173c23c25b4..2a8c5670b254 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -3106,26 +3106,31 @@ static void ctx_sched_out(struct perf_event_context *ctx,
> > static int context_equiv(struct perf_event_context *ctx1,
> > struct perf_event_context *ctx2)
> > {
> > + struct perf_event_context *parent_ctx1, *parent_ctx2;
> > +
> > lockdep_assert_held(&ctx1->lock);
> > lockdep_assert_held(&ctx2->lock);
> >
> > + parent_ctx1 = rcu_dereference(ctx1->parent_ctx);
> > + parent_ctx2 = rcu_dereference(ctx2->parent_ctx);
>
> Bah.
>
> Why are you fixing all this sparse crap and making the code worse?
Hi Peter,
Sparse is quite noisy and we need to eliminate false-positives, right?
__rcu will tell the developer, this pointer could change and he needs to
take the required steps to make sure the code doesn't break.
Thanks
Amol
_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees
next prev parent reply other threads:[~2020-02-10 12:59 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-08 14:46 [Linux-kernel-mentees] [PATCH] events: Annotate parent_ctx with __rcu Amol Grover
2020-02-10 9:36 ` Peter Zijlstra
2020-02-10 12:59 ` Amol Grover [this message]
2020-02-10 13:34 ` Peter Zijlstra
2020-02-10 16:47 ` Amol Grover
2020-02-10 17:08 ` Joel Fernandes
2020-02-13 6:44 ` Amol Grover
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200210125948.GA16485@workstation-portable \
--to=frextrite@gmail.com \
--cc=acme@kernel.org \
--cc=alexander.shishkin@linux.intel.com \
--cc=joel@joelfernandes.org \
--cc=jolsa@redhat.com \
--cc=linux-kernel-mentees@lists.linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=madhuparnabhowmik10@gmail.com \
--cc=mark.rutland@arm.com \
--cc=mingo@redhat.com \
--cc=namhyung@kernel.org \
--cc=paulmck@kernel.org \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).