From: Andi Kleen <andi@firstfloor.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Andi Kleen <andi@firstfloor.org>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Ingo Molnar <mingo@redhat.com>,
Arjan van de Ven <arjan@infradead.org>,
Hugh Dickins <hugh@veritas.com>,
Ulrich Drepper <drepper@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH, v3] shmat: introduce flag SHM_MAP_NOT_FIXED
Date: Wed, 8 Oct 2008 13:02:43 +0200 [thread overview]
Message-ID: <20081008110243.GN7971@one.firstfloor.org> (raw)
In-Reply-To: <20081008112037.6fa37c0b@lxorguk.ukuu.org.uk>
On Wed, Oct 08, 2008 at 11:20:37AM +0100, Alan Cox wrote:
> > That is racy when multi threaded because shmat() doesn't replace, so you
> > would need to munmap() inbetween and someone else could steal the area
> > then. Yes you could stick a loop around it. It could livelock.
> > No, it's not a good interface I would advocate.
>
> You could just use pthread mutexes in your application. The rôle of the
malloc() can call mmap, so that would require putting a mutex around
each malloc(). Good luck finding them all.
> kernel is not to provide nappies for people who think programming is too
> hard but to provide services that can be used to build applications.
Outsourcing kernel locking to user space is not the way to go.
-Andi
--
ak@linux.intel.com
WARNING: multiple messages have this Message-ID (diff)
From: Andi Kleen <andi@firstfloor.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Andi Kleen <andi@firstfloor.org>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Ingo Molnar <mingo@redhat.com>,
Arjan van de Ven <arjan@infradead.org>,
Hugh Dickins <hugh@veritas.com>,
Ulrich Drepper <drepper@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH, v3] shmat: introduce flag SHM_MAP_NOT_FIXED
Date: Wed, 8 Oct 2008 13:02:43 +0200 [thread overview]
Message-ID: <20081008110243.GN7971@one.firstfloor.org> (raw)
In-Reply-To: <20081008112037.6fa37c0b@lxorguk.ukuu.org.uk>
On Wed, Oct 08, 2008 at 11:20:37AM +0100, Alan Cox wrote:
> > That is racy when multi threaded because shmat() doesn't replace, so you
> > would need to munmap() inbetween and someone else could steal the area
> > then. Yes you could stick a loop around it. It could livelock.
> > No, it's not a good interface I would advocate.
>
> You could just use pthread mutexes in your application. The role of the
malloc() can call mmap, so that would require putting a mutex around
each malloc(). Good luck finding them all.
> kernel is not to provide nappies for people who think programming is too
> hard but to provide services that can be used to build applications.
Outsourcing kernel locking to user space is not the way to go.
-Andi
--
ak@linux.intel.com
--
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next prev parent reply other threads:[~2008-10-08 10:56 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-07 16:15 [PATCH, v3] shmat: introduce flag SHM_MAP_NOT_FIXED Kirill A. Shutemov
2008-10-07 16:15 ` Kirill A. Shutemov
2008-10-07 16:31 ` KOSAKI Motohiro
2008-10-07 16:31 ` KOSAKI Motohiro
2008-10-07 21:10 ` Andi Kleen
2008-10-07 21:10 ` Andi Kleen
2008-10-07 21:38 ` KOSAKI Motohiro
2008-10-07 21:38 ` KOSAKI Motohiro
2008-10-07 23:23 ` Andi Kleen
2008-10-07 23:23 ` Andi Kleen
2008-10-07 23:05 ` Alan Cox
2008-10-07 23:05 ` Alan Cox
2008-10-07 23:20 ` Andi Kleen
2008-10-07 23:20 ` Andi Kleen
2008-10-07 23:40 ` Alan Cox
2008-10-07 23:40 ` Alan Cox
2008-10-07 23:57 ` Andi Kleen
2008-10-07 23:57 ` Andi Kleen
2008-10-08 8:33 ` Alan Cox
2008-10-08 8:33 ` Alan Cox
2008-10-08 8:34 ` Alan Cox
2008-10-08 8:34 ` Alan Cox
2008-10-08 8:43 ` Andi Kleen
2008-10-08 8:43 ` Andi Kleen
2008-10-08 8:58 ` Alan Cox
2008-10-08 8:58 ` Alan Cox
2008-10-08 9:11 ` Andi Kleen
2008-10-08 9:11 ` Andi Kleen
2008-10-08 10:20 ` Alan Cox
2008-10-08 10:20 ` Alan Cox
2008-10-08 11:02 ` Andi Kleen [this message]
2008-10-08 11:02 ` Andi Kleen
2008-10-08 12:46 ` Alan Cox
2008-10-08 12:46 ` Alan Cox
2008-10-07 16:54 ` Alan Cox
2008-10-07 16:54 ` Alan Cox
[not found] ` <1223396117-8118-1-git-send-email-kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>
2008-10-08 8:57 ` Michael Kerrisk
2008-10-08 8:57 ` Michael Kerrisk
2008-10-08 8:57 ` Michael Kerrisk
[not found] ` <517f3f820810080157j3994ff10j8518178af02e5b22-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2008-10-08 9:35 ` Kirill A. Shutemov
2008-10-08 9:35 ` Kirill A. Shutemov
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