Patch "fscache: Fix the default for fscache_maybe_release_page()" has been added to the 4.14-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    fscache: Fix the default for fscache_maybe_release_page()

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fscache-fix-the-default-for-fscache_maybe_release_page.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 98801506552593c9b8ac11021b0cdad12cab4f6b Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Tue, 2 Jan 2018 10:02:19 +0000
Subject: fscache: Fix the default for fscache_maybe_release_page()

From: David Howells <dhowells@redhat.com>

commit 98801506552593c9b8ac11021b0cdad12cab4f6b upstream.

Fix the default for fscache_maybe_release_page() for when the cookie isn't
valid or the page isn't cached.  It mustn't return false as that indicates
the page cannot yet be freed.

The problem with the default is that if, say, there's no cache, but a
network filesystem's pages are using up almost all the available memory, a
system can OOM because the filesystem ->releasepage() op will not allow
them to be released as fscache_maybe_release_page() incorrectly prevents
it.

This can be tested by writing a sequence of 512MiB files to an AFS mount.
It does not affect NFS or CIFS because both of those wrap the call in a
check of PG_fscache and it shouldn't bother Ceph as that only has
PG_private set whilst writeback is in progress.  This might be an issue for
9P, however.

Note that the pages aren't entirely stuck.  Removing a file or unmounting
will clear things because that uses ->invalidatepage() instead.

Fixes: 201a15428bd5 ("FS-Cache: Handle pages pending storage that get evicted under OOM conditions")
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 include/linux/fscache.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -755,7 +755,7 @@ bool fscache_maybe_release_page(struct f
 {
 	if (fscache_cookie_valid(cookie) && PageFsCache(page))
 		return __fscache_maybe_release_page(cookie, page, gfp);
-	return false;
+	return true;
 }
 
 /**


Patches currently in stable-queue which might be from dhowells@redhat.com are

queue-4.14/fscache-fix-the-default-for-fscache_maybe_release_page.patch