[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>

diff --git a/fs/gfs2/ops_address.c b/fs/gfs2/ops_address.c
index 90c2879..30c1562 100644 (file)
--- 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;