@@ -4468,6 +4468,28 @@ static char *page_getlink(struct dentry * dentry, struct page **ppage)
return kaddr;
}
+/* get the link contents from pagecache under RCU */
+static char *page_getlink_rcu(struct dentry * dentry, struct page **ppage)
+{
+ char *kaddr;
+ struct page *page;
+ struct address_space *mapping = dentry->d_inode->i_mapping;
+ page = find_get_page(mapping, 0);
+ if (page &&
+ (!PageUptodate(page) || PageHighMem(page))) {
+ put_page(page);
+ page = NULL;
+ }
+ if (!page) {
+ *ppage = ERR_PTR(-ECHILD);
+ return NULL;
+ }
+ *ppage = page;
+ kaddr = page_address(page);
+ nd_terminate_link(kaddr, dentry->d_inode->i_size, PAGE_SIZE - 1);
+ return kaddr;
+}
+
int page_readlink(struct dentry *dentry, char __user *buffer, int buflen)
{
struct page *page = NULL;
@@ -4484,8 +4506,9 @@ void *page_follow_link_light(struct dentry *dentry, struct nameidata *nd)
{
struct page *page = NULL;
if (nd->flags & LOOKUP_RCU)
- return ERR_PTR(-ECHILD);
- nd_set_link(nd, page_getlink(dentry, &page));
+ nd_set_link(nd, page_getlink_rcu(dentry, &page));
+ else
+ nd_set_link(nd, page_getlink(dentry, &page));
return page;
}
EXPORT_SYMBOL(page_follow_link_light);
@@ -4495,7 +4518,8 @@ void page_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
struct page *page = cookie;
if (page) {
- kunmap(page);
+ if (!(nd->flags & LOOKUP_LINK_RCU))
+ kunmap(page);
page_cache_release(page);
}
}
If the symlink has already be been read-in, then page_follow_link_light can succeed in RCU-walk mode. page_getlink_rcu() is added to support this. With this many filesystems can follow links in RCU-walk mode when everything is cached. This includes ext?fs and others. If the page is a HighMem page we do *not* try to kmap_atomic, but simply give up - only page_address() is used. This is because we need to be able to sleep while holding the address of the page, particularly over calls to do_last() which can be quite slow and in particular takes a mutex. If this were a problem, then copying into a GFP_ATOMIC allocation might be a workable solution. Signed-off-by: NeilBrown <neilb@suse.de> --- fs/namei.c | 30 +++++++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html