[GFS2] Patch to fix mmap of stuffed files

If a stuffed file is mmaped and a page fault is generated at some offset
above the initial page, we need to create a zero page to hang the buffer
heads off before we can unstuff the file. This is a fix for bz #236087

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 14 insertions, 3 deletions

diff --git a/fs/gfs2/ops_address.c b/fs/gfs2/ops_address.c
index 90c287932d58..30c15622174f 100644
--- a/fs/gfs2/ops_address.c
+++ b/fs/gfs2/ops_address.c
@@ -197,7 +197,19 @@ static int stuffed_readpage(struct gfs2_inode *ip, struct page *page)
         void *kaddr;
         int error;
 
-        BUG_ON(page->index);
+        /*
+         * Due to the order of unstuffing files and ->nopage(), we can be
+         * asked for a zero page in the case of a stuffed file being extended,
+         * so we need to supply one here. It doesn't happen often.
+         */
+        if (unlikely(page->index)) {
+                kaddr = kmap_atomic(page, KM_USER0);
+                memset(kaddr, 0, PAGE_CACHE_SIZE);
+                kunmap_atomic(kaddr, KM_USER0);
+                flush_dcache_page(page);
+                SetPageUptodate(page);
+                return 0;
+        }
 
         error = gfs2_meta_inode_buffer(ip, &dibh);
         if (error)
@@ -208,9 +220,8 @@ static int stuffed_readpage(struct gfs2_inode *ip, struct page *page)
                ip->i_di.di_size);
         memset(kaddr + ip->i_di.di_size, 0, PAGE_CACHE_SIZE - ip->i_di.di_size);
         kunmap_atomic(kaddr, KM_USER0);
-
+        flush_dcache_page(page);
         brelse(dibh);
-
         SetPageUptodate(page);
 
         return 0;