linux-kernel - Re: [PATCH] signal: annotate siglock acquisition

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Date:	Sat, 25 Sep 2010 20:33:08 +0900
From:	Namhyung Kim <namhyung@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] signal: annotate siglock acquisition

On Sat, Sep 25, 2010 at 18:42, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le samedi 25 septembre 2010 à 18:21 +0900, Namhyung Kim a écrit :
>> @@ -1403,7 +1404,9 @@ int send_sigqueue(struct sigqueue *q, struct task_struct *t, int group)
>>       BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
>>
>>       ret = -1;
>> -     if (!likely(lock_task_sighand(t, &flags)))
>> +     if (likely(lock_task_sighand(t, &flags)))
>> +             __acquire(&t->sighand->siglock);
>> +     else
>>               goto ret;
>>
>>       ret = 1; /* the signal is ignored */
>
> making sparse happy is good, but changing a likely clause is not,
> unless you meant it ;)
>
> maybe -->
>
>        if (!likely(lock_task_sighand(t, &flags)))
>                goto ret;
>        else
>                __acquire(&t->sighand->siglock);
>
>
>
>

What's the difference? I didn't change the semantics of likely clause
but simply exchange the order of then-else part because IMHO a
negative expression make it hard to understand, generally.
I've checked compiled binaries for both cases on x86 and they
produced exactly same code.

Thanks.


-- 
Regards,
Namhyung Kim
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