libceph: fix handling of short returns from get_user_pages

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>

1 files changed, 13 insertions, 5 deletions

diff --git a/net/ceph/pagevec.c b/net/ceph/pagevec.c
index 1a040e64c69..cd9c21df87d 100644
--- a/net/ceph/pagevec.c
+++ b/net/ceph/pagevec.c
@@ -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);