Commit e8ecde25 authored by Al Viro's avatar Al Viro
Browse files

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: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 60b7eca1

Documentation/filesystems/porting

+5 −1
Original line number Diff line number Diff line
@@ -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

fs/nfs/dir.c

+2 −3
Original line number Diff line number Diff line
@@ -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);

mm/shmem.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

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