linux-kernel - Re: [PATCH] Don't set sempid in semctl syscall.

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Message-ID: <20160226221551.GA18437@linux-uzut.site>
Date:	Fri, 26 Feb 2016 14:15:51 -0800
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Manfred Spraul <manfred@...orfullife.com>
Cc:	PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>,
	akpm@...ux-foundation.org, herton@...hat.com,
	penguin-kernel@...ove.sakura.ne.jp, rientjes@...gle.com,
	joe@...ches.com, linux-kernel@...r.kernel.org,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH] Don't set sempid in semctl syscall.

On Fri, 26 Feb 2016, Manfred Spraul wrote:

This is a user-visible change, adding mtk.

>Hi,
>
>On 02/26/2016 01:21 PM, PrasannaKumar Muralidharan wrote:
>>From: PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>
>>
>>As described in bug #112271 (bugzilla.kernel.org/show_bug.cgi?id=112271)
>>don't set sempid in semctl syscall. Set sempid only when semop is called.
>I disagree with the bug report:

This bug report really lacks any kind of motivation for this patch, not
posix-friendly is pretty bogus. Albeit we are doing some false publicity.

>
>sempid is (and always was on Linux) the pid of the last task that modified the semaphore:
>It is updated for semop, SETVAL and undo adjustment on process exit.
>And - that is a bug: sempid is not updated for SETALL :-(

Code-wise yeah, but we have such things in our docs (semctl.2):

       GETPID    Return the value of sempid for the semnum-th semaphore of the  set  (i.e.,  the  PID  of  the
                  process  that  executed  the last semop(2) call for the semnum-th semaphore of the set).  The
                  calling process must have read permission on the semaphore set.

Furthermore, semop.2 is very explicit about sempid. That said, I am also weary of this
change because we've been setting semval for semctl for so long.
stuff).

Thanks,
Davidlohr