linux-kernel - Re: [PATCH v2 3/3] NFS: Fix a memory leak in nfs

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Date:	Wed, 1 Dec 2010 17:05:43 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Trond Myklebust <Trond.Myklebust@...app.com>,
	Hugh Dickins <hughd@...gle.com>,
	Nick Piggin <npiggin@...nel.dk>,
	Nick Bowler <nbowler@...iptictech.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-nfs@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Christoph Hellwig <hch@....de>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2 3/3] NFS: Fix a memory leak in nfs_readdir

On Wed, Dec 1, 2010 at 3:36 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Wed, 1 Dec 2010 15:31:11 -0800
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>>
>> Ergo: vmscan has a locked page leads to the filesystem being
>> guaranteed to not be unmounted.  And that, in turn, guarantees that
>> the module won't be unloaded until the machine has gone through an
>> idle cycle.
>
> The page isn't attached to the address_space any more:

Did you even read the email?

Here, let me quote the important parts:

  "module won't be unloaded until the machine has gone through an idle cycle"

  "This is pretty much how all the module races are handled. Doing module
   ref-counts per page (or per packet in flight for things like
   networking) would be prohibitively expensive."

IOW, the whole "stop_machine()" part is fundamental. That whole
"module unload won't happen until we've gone through an idle cycle" is
EXACTLY why we don't need to have the page attached or ref-counted -
we're still safe.

                    Linus
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