libceph: fix handling of short returns from get_user_pages
Sage Weil [Thu, 3 Mar 2011 00:55:21 +0000 (16:55 -0800)]
get_user_pages() can return fewer pages than we ask for.  We were returning
a bogus pointer/error code in that case.  Instead, loop until we get all
the pages we want or get an error we can return to the caller.

Signed-off-by: Sage Weil <sage@newdream.net>

net/ceph/pagevec.c

index 1a040e6..cd9c21d 100644 (file)
@@ -16,22 +16,30 @@ struct page **ceph_get_direct_page_vector(const char __user *data,
                                          int num_pages, bool write_page)
 {
        struct page **pages;
-       int rc;
+       int got = 0;
+       int rc = 0;
 
        pages = kmalloc(sizeof(*pages) * num_pages, GFP_NOFS);
        if (!pages)
                return ERR_PTR(-ENOMEM);
 
        down_read(&current->mm->mmap_sem);
-       rc = get_user_pages(current, current->mm, (unsigned long)data,
-                           num_pages, write_page, 0, pages, NULL);
+       while (got < num_pages) {
+               rc = get_user_pages(current, current->mm,
+                   (unsigned long)data + ((unsigned long)got * PAGE_SIZE),
+                   num_pages - got, write_page, 0, pages + got, NULL);
+               if (rc < 0)
+                       break;
+               BUG_ON(rc == 0);
+               got += rc;
+       }
        up_read(&current->mm->mmap_sem);
-       if (rc < num_pages)
+       if (rc < 0)
                goto fail;
        return pages;
 
 fail:
-       ceph_put_page_vector(pages, rc > 0 ? rc : 0, false);
+       ceph_put_page_vector(pages, got, false);
        return ERR_PTR(rc);
 }
 EXPORT_SYMBOL(ceph_get_direct_page_vector);