From: Linus Torvalds <torvalds@osdl.org>
To: Robin Holt <holt@sgi.com>
Cc: Simon Derr <Simon.Derr@bull.net>, Paul Jackson <pj@sgi.com>,
Andrew Morton <akpm@osdl.org>,
Dinakar Guniguntala <dino@in.ibm.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2.6.12-rc4] cpuset exit NULL dereference fix
Date: Thu, 26 May 2005 08:44:37 -0700 (PDT) [thread overview]
Message-ID: <Pine.LNX.4.58.0505260840470.2307@ppc970.osdl.org> (raw)
In-Reply-To: <20050526120859.GD29852@lnx-holt.americas.sgi.com>
On Thu, 26 May 2005, Robin Holt wrote:
>
> Why not change the atomic into a lock and a refcount. Grab the lock before
> each increment/decrement of the refcount and only continue with the removal
> code when the refcount reaches 0.
For this, there is a nice
atomic_dec_and_lock()
function that is the same as "atomic_dec_and_test()", except it grabs the
lock if the count decrements to zero.
I'm surprised people haven't picked up on it - it's been around for a
while, the VFS layer uses it for some quite fundamental data structures
(inode and dcache refcounts), and it's even documented in "atomic_ops.txt"
And it's _designed_ for refcountign things like this.
Basic rule of kernel programming: if a globally visible object does not
have a refcount, IT IS A BUG.
Linus
next prev parent reply other threads:[~2005-05-26 15:43 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-05-26 8:25 Paul Jackson
2005-05-26 9:00 ` Simon Derr
2005-05-26 12:08 ` Robin Holt
2005-05-26 15:44 ` Linus Torvalds [this message]
2005-05-26 18:46 ` Paul Jackson
2005-05-26 20:46 ` Paul Jackson
2005-05-26 13:54 ` Dinakar Guniguntala
2005-05-26 20:07 ` Paul Jackson
2005-05-27 0:24 ` Paul Jackson
2005-05-26 23:40 ` Paul Jackson
2005-05-27 8:07 ` Simon Derr
2005-05-27 8:44 ` Paul Jackson
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