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

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Date:	Wed, 1 Dec 2010 14:43:14 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Neil Brown <neilb@...e.de>
Cc:	Trond Myklebust <Trond.Myklebust@...app.com>,
	Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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>,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: [PATCH v2 3/3] NFS: Fix a memory leak in nfs_readdir

On Thu, 2 Dec 2010 08:29:13 +1100
Neil Brown <neilb@...e.de> wrote:

> > > 
> > > However, while reading Documentation/filesystems/vfs.txt (in order to
> > > add documentation for freepage) I was surprised to read that the
> > > ->releasepage() is itself supposed to be allowed to actually remove the
> > > page from the address space if it so desires.
> > 
> > That doesn't sound right.  It came from Neil in 2006.
> > 
> > Neil, what were you thinking there?   Did you find such a ->releasepage()?
> 
> Nope, no idea, sorry.
> 
> No releasepage functions do anything like that, and no call sites suggest it
> could be a possibility.  Quite the reverse - they are likely to remove the
> page from the mapping without checking that it is still in the mapping.
> 
> So that sentence should be deleted.

This?

From: Andrew Morton <akpm@...ux-foundation.org>

->releasepage() does not remove the page from the mapping.

Cc: Neil Brown <neilb@...e.de>
Cc: Trond Myklebust <Trond.Myklebust@...app.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 Documentation/filesystems/vfs.txt |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff -puN Documentation/filesystems/vfs.txt~documentation-filesystems-vfstxt-fix-repeasepage-description Documentation/filesystems/vfs.txt
--- a/Documentation/filesystems/vfs.txt~documentation-filesystems-vfstxt-fix-repeasepage-description
+++ a/Documentation/filesystems/vfs.txt
@@ -660,11 +660,10 @@ struct address_space_operations {
   releasepage: releasepage is called on PagePrivate pages to indicate
         that the page should be freed if possible.  ->releasepage
         should remove any private data from the page and clear the
-        PagePrivate flag.  It may also remove the page from the
-        address_space.  If this fails for some reason, it may indicate
-        failure with a 0 return value.
-	This is used in two distinct though related cases.  The first
-        is when the VM finds a clean page with no active users and
+        PagePrivate flag. If releasepage() fails for some reason, it must
+	indicate failure with a 0 return value.
+	releasepage() is used in two distinct though related cases.  The
+	first is when the VM finds a clean page with no active users and
         wants to make it a free page.  If ->releasepage succeeds, the
         page will be removed from the address_space and become free.
 
_

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