1 files changed, 13 insertions, 3 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 5de7633e1dbe..d97d1ad55473 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1023,8 +1023,17 @@ find_page:
                                         ra, filp, page,
                                         index, last_index - index);
                 }
-                if (!PageUptodate(page))
-                        goto page_not_up_to_date;
+                if (!PageUptodate(page)) {
+                        if (inode->i_blkbits == PAGE_CACHE_SHIFT ||
+                                        !mapping->a_ops->is_partially_uptodate)
+                                goto page_not_up_to_date;
+                        if (TestSetPageLocked(page))
+                                goto page_not_up_to_date;
+                        if (!mapping->a_ops->is_partially_uptodate(page,
+                                                                desc, offset))
+                                goto page_not_up_to_date_locked;
+                        unlock_page(page);
+                }
 page_ok:
                 /*
                  * i_size must be checked after we know the page is Uptodate.
@@ -1094,6 +1103,7 @@ page_not_up_to_date:
                 if (lock_page_killable(page))
                         goto readpage_eio;
 
+page_not_up_to_date_locked:
                 /* Did it get truncated before we got the lock? */
                 if (!page->mapping) {
                         unlock_page(page);
@@ -1869,7 +1879,7 @@ void iov_iter_advance(struct iov_iter *i, size_t bytes)
                  * The !iov->iov_len check ensures we skip over unlikely
                  * zero-length segments (without overruning the iovec).
                  */
-                while (bytes || unlikely(!iov->iov_len && i->count)) {
+                while (bytes || unlikely(i->count && !iov->iov_len)) {
                         int copy;
 
                         copy = min(bytes, iov->iov_len - base);