Make sure that highmem pages are not added to symlink page cache

inode_nohighmem() is sufficient to make sure that page_get_link()
won't try to allocate a highmem page.  Moreover, it is sufficient
to make sure that page_symlink/__page_symlink won't do the same
thing.  However, any filesystem that manually preseeds the symlink's
page cache upon symlink(2) needs to make sure that the page it
inserts there won't be a highmem one.

Fortunately, only nfs and shmem have run afoul of that...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index 0f88e60..f1b87d8 100644 (file)
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -508,7 +508,11 @@ in your dentry operations instead.
 [mandatory]
        any symlink that might use page_follow_link_light/page_put_link() must
        have inode_nohighmem(inode) called before anything might start playing with
-       its pagecache.
+       its pagecache.  No highmem pages should end up in the pagecache of such
+       symlinks.  That includes any preseeding that might be done during symlink
+       creation.  __page_symlink() will honour the mapping gfp flags, so once
+       you've done inode_nohighmem() it's safe to use, but if you allocate and
+       insert the page manually, make sure to use the right gfp flags.
 --
 [mandatory]
        ->follow_link() is replaced with ->get_link(); same API, except that

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index ce5a218..8a05309 100644 (file)
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1894,15 +1894,14 @@ int nfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
        attr.ia_mode = S_IFLNK | S_IRWXUGO;
        attr.ia_valid = ATTR_MODE;
 
-       page = alloc_page(GFP_HIGHUSER);
+       page = alloc_page(GFP_USER);
        if (!page)
                return -ENOMEM;
 
-       kaddr = kmap_atomic(page);
+       kaddr = page_address(page);
        memcpy(kaddr, symname, pathlen);
        if (pathlen < PAGE_SIZE)
                memset(kaddr + pathlen, 0, PAGE_SIZE - pathlen);
-       kunmap_atomic(kaddr);
 
        trace_nfs_symlink_enter(dir, dentry);
        error = NFS_PROTO(dir)->symlink(dir, dentry, page, pathlen, &attr);

diff --git a/mm/shmem.c b/mm/shmem.c
index 5813b7f..642471b 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2469,6 +2469,7 @@ static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *s
                inode->i_op = &shmem_short_symlink_operations;
                inode->i_link = info->symlink;
        } else {
+               inode_nohighmem(inode);
                error = shmem_getpage(inode, 0, &page, SGP_WRITE, NULL);
                if (error) {
                        iput(inode);
@@ -2476,7 +2477,6 @@ static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *s
                }
                inode->i_mapping->a_ops = &shmem_aops;
                inode->i_op = &shmem_symlink_inode_operations;
-               inode_nohighmem(inode);
                memcpy(page_address(page), symname, len);
                SetPageUptodate(page);
                set_page_dirty(page);