From: Peter Zijlstra <peterz@infradead.org>
To: Amol Grover <frextrite@gmail.com>
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 14:34:59 +0100 [thread overview]
Message-ID: <20200210133459.GJ14897@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200210125948.GA16485@workstation-portable>
On Mon, Feb 10, 2020 at 06:29:48PM +0530, Amol Grover wrote:
> 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:
> > > @@ -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?
Dunno, I've been happy just ignoring it all.
> __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.
I know what it does; what I don't know is why you need to make the code
worse. In paricular, __rcu doesn't mandate rcu_dereference(), esp. not
when you're actually holding the write side lock.
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next prev parent reply other threads:[~2020-02-10 13:35 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
2020-02-10 13:34 ` Peter Zijlstra [this message]
2020-02-10 16:47 ` Amol Grover
2020-02-10 17:08 ` Joel Fernandes
2020-02-13 6:44 ` Amol Grover
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