linux-kernel - Re: sched: Fix signedness bug in yield

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Date:	Fri, 22 Feb 2013 12:12:25 +0530
From:	Raghavendra KT <raghavendra.kt.linux@...il.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>, dan.carpenter@...cle.com
Cc:	Ingo Molnar <mingo@...nel.org>, Shuah Khan <shuahkhan@...il.com>,
	peterz@...radead.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	torvalds@...ux-foundation.org
Subject: Re: sched: Fix signedness bug in yield_to()

On Fri, Feb 22, 2013 at 4:56 AM, Marcelo Tosatti <mtosatti@...hat.com> wrote:
> On Thu, Feb 21, 2013 at 09:56:54AM +0100, Ingo Molnar wrote:
>>
>> * Shuah Khan <shuahkhan@...il.com> wrote:
>>
>> > On Tue, Feb 19, 2013 at 7:27 PM, Linux Kernel Mailing List
>> > <linux-kernel@...r.kernel.org> wrote:
>> > > Gitweb:     http://git.kernel.org/linus/;a=commit;h=c3c186403c6abd32e719f005f0af950155a9e54d
>> > > Commit:     c3c186403c6abd32e719f005f0af950155a9e54d
>> > > Parent:     e0a79f529d5ba2507486d498b25da40911d95cf6
>> > > Author:     Dan Carpenter <dan.carpenter@...cle.com>
>> > > AuthorDate: Tue Feb 5 14:37:51 2013 +0300
>> > > Committer:  Ingo Molnar <mingo@...nel.org>
>> > > CommitDate: Tue Feb 5 12:59:29 2013 +0100
>> > >
>> > >     sched: Fix signedness bug in yield_to()
>> > >
>> > >     In 7b270f6099 "sched: Bail out of yield_to when source and
>> > >     target runqueue has one task" we changed this to store -ESRCH so
>> > >     it needs to be signed.
>> >
>> > Dan, Ingo,
>> >
>> > I can't find the 7b270f6099 "sched: Bail out of yield_to when
>> > source and target runqueue has one task" in the latest Linus's
>> > git. Am I missing something.
>> >
>> > The current kenel/sched/core.c doesn't have the code from the
>> > associated patch https://patchwork.kernel.org/patch/2016651/
>>
>> As per the lkml discussion that one was supposed to go upstream
>> via the KVM tree. Marcelo?
>
> commit c3c186403c6abd32e719f005f0af950155a9e54d
> Author: Dan Carpenter <dan.carpenter@...cle.com>
> Date:   Tue Feb 5 14:37:51 2013 +0300
>
>     sched: Fix signedness bug in yield_to()
>
>     In 7b270f6099 "sched: Bail out of yield_to when source and
>     target runqueue has one task" we changed this to store -ESRCH so
>     it needs to be signed.
>
>     Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
>     Cc: Peter Zijlstra <peterz@...radead.org>
>     Cc: kbuild@...org
>     Cc: Steven Rostedt <rostedt@...dmis.org>
>     Cc: Mike Galbraith <efault@....de>
>     Link: http://lkml.kernel.org/r/20130205113751.GA20521@elgon.mountain
>     Signed-off-by: Ingo Molnar <mingo@...nel.org>
>

IIUC, we are only changing variable in yield_to  from bool to int.
I am curious whether we need changes in struct  sched_class (sched.h)

 bool (*yield_to_task) (struct rq *rq, struct task_struct *p, bool preempt);
==>
int (*yield_to_task) (struct rq *rq, struct task_struct *p, bool preempt);

otherwise we would assign bool value  to int here

 yielded = curr->sched_class->yield_to_task(rq, p, preempt);

this return values also cascaded to kvm_main.c.

If we need to patchup entire thing, I can cook a correction patch.

Thanks and Regards
Raghu
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