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 cc: stable@vger.kernel.org # 2.6.32+ ---

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

diff --git a/include/linux/fscache.h b/include/linux/fscache.h index f4ff47d4a893..fe0c349684fa 100644 --- a/include/linux/fscache.h +++ b/include/linux/fscache.h @@ -755,7 +755,7 @@ bool fscache_maybe_release_page(struct fscache_cookie *cookie, { if (fscache_cookie_valid(cookie) && PageFsCache(page)) return __fscache_maybe_release_page(cookie, page, gfp); - return false; + return true; }

/**