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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>
This commit is contained in:
Al Viro 2016-01-14 17:52:59 -05:00
parent 60b7eca1dc
commit e8ecde25f5
3 changed files with 8 additions and 5 deletions
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6
Documentation/filesystems/porting
View File

@ -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

5
fs/nfs/dir.c
View File

@ -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);

2
mm/shmem.c
View File

@ -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);