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From: Andrew Morton <akpm@linux-foundation.org>
To: Tilman Schmidt <tilman@imap.cc>
Cc: Karsten Keil <kkeil@suse.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	i4ldeveloper@listserv.isdn4linux.de,
	linux-serial@vger.kernel.org, Hansjoerg Lipp <hjlipp@web.de>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>, Greg KH <greg@kroah.com>
Subject: Re: [PATCH] drivers/isdn/gigaset: new M101 driver
Date: Sun, 4 Feb 2007 20:58:17 -0800	[thread overview]
Message-ID: <20070204205817.fe686375.akpm@linux-foundation.org> (raw)
In-Reply-To: <45C68B71.6050904@imap.cc>

On Mon, 05 Feb 2007 02:42:09 +0100 Tilman Schmidt <tilman@imap.cc> wrote:

> Am 04.02.2007 02:56 schrieb Andrew Morton:
> > On Sun, 04 Feb 2007 02:32:41 +0100 Tilman Schmidt <tilman@imap.cc> wrote:
> > 
> >>>> +	spin_lock_irqsave(&cs->cmdlock, flags);
> >>>> +	cb = cs->cmdbuf;
> >>>> +	spin_unlock_irqrestore(&cs->cmdlock, flags);
> >>> It is doubtful if the locking here does anything useful.
> >> It assures atomicity when reading the cs->cmdbuf pointer.
> > 
> > I think it's bogus.  If the quantity being copied here is more than 32-bits
> > then yes, a lock is appropriate.  But if it's a single word then it's
> > unlikely that the locking does anything useful.  Or there might be a bug
> > here.
> 
> It's a pointer. Are reads and writes of pointer sized objects
> guaranteed to be atomic on every platform?

Yup - we make the same assumption about longs in various places.

It's a bit strange to read a pointer which can be changing at the
same time.  Because the local copy will no longer represent the
thing which it was just copied from.

  reply	other threads:[~2007-02-05  4:58 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <200702012112.l11LCOO4016557@lx1.pxnet.com>
2007-02-02  1:13 ` Andrew Morton
2007-02-03 16:09   ` Greg KH
2007-02-04  0:26     ` Tilman Schmidt
2007-02-12 18:47       ` Greg KH
2007-02-12 23:49         ` Tilman Schmidt
2007-02-04  1:32   ` Tilman Schmidt
2007-02-04  1:56     ` Andrew Morton
2007-02-05  1:42       ` Tilman Schmidt
2007-02-05  4:58         ` Andrew Morton [this message]
2007-02-05 12:29           ` Tilman Schmidt

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