Date: Fri, 4 Jan 2008 16:49:06 -0800 (PST)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Arjan van de Ven <arjan@infradead.org>
cc: Ingo Molnar <mingo@elte.hu>, Theodore Tso <tytso@mit.edu>,
       Andi Kleen <andi@firstfloor.org>, Christoph Lameter <clameter@sgi.com>,
       Willy Tarreau <w@1wt.eu>, Steven Rostedt <rostedt@goodmis.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       LKML <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Christoph Hellwig <hch@infradead.org>,
       "Rafael J. Wysocki" <rjw@sisk.pl>
Subject: Re: [patch] slub: provide /proc/slabinfo
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On Fri, 4 Jan 2008, Arjan van de Ven wrote:
> 
> this is the part I'm not very thrilled about... at least on first sight 
> it looks like a user can now hold the read sem over system calls, and 
> for as long as it wants.

No, you misunderstand how seq-files work.

The start/stop sequence is done only overone single kernel buffer 
instance, not over the whole open/close (or even the copy to user space).

It's expressly designed so that you can hold locks (including spinlocks 
etc), and will not do any blocking ops (well - your *callbacks* can you 
blocking ops, but the seq_file stuff itself won't) between start/stop.

		Linus
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