Btrfs: fix the mismatch of page->mapping

commit 600a45e1d5e376f679ff9ecc4ce9452710a6d27c
(Btrfs: fix deadlock on page lock when doing auto-defragment)
fixes the deadlock on page, but it also introduces another bug.

A page may have been truncated after unlock & lock.
So we need to find it again to get the right one.

And since we've held i_mutex lock, inode size remains unchanged and
we can drop isize overflow checks.

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 19 insertions, 16 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 45910d4b8f65..de46fa218590 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -871,6 +871,7 @@ static int cluster_pages_for_defrag(struct inode *inode,
         u64 isize = i_size_read(inode);
         u64 page_start;
         u64 page_end;
+        u64 page_cnt;
         int ret;
         int i;
         int i_done;
@@ -879,19 +880,21 @@ static int cluster_pages_for_defrag(struct inode *inode,
         struct extent_io_tree *tree;
         gfp_t mask = btrfs_alloc_write_mask(inode->i_mapping);
 
-        if (isize == 0)
-                return 0;
         file_end = (isize - 1) >> PAGE_CACHE_SHIFT;
+        if (!isize || start_index > file_end)
+                return 0;
+
+        page_cnt = min_t(u64, (u64)num_pages, (u64)file_end - start_index + 1);
 
         ret = btrfs_delalloc_reserve_space(inode,
-                                           num_pages << PAGE_CACHE_SHIFT);
+                                           page_cnt << PAGE_CACHE_SHIFT);
         if (ret)
                 return ret;
         i_done = 0;
         tree = &BTRFS_I(inode)->io_tree;
 
         /* step one, lock all the pages */
-        for (i = 0; i < num_pages; i++) {
+        for (i = 0; i < page_cnt; i++) {
                 struct page *page;
 again:
                 page = find_or_create_page(inode->i_mapping,
@@ -913,6 +916,15 @@ again:
                         btrfs_start_ordered_extent(inode, ordered, 1);
                         btrfs_put_ordered_extent(ordered);
                         lock_page(page);
+                        /*
+                         * we unlocked the page above, so we need check if
+                         * it was released or not.
+                         */
+                        if (page->mapping != inode->i_mapping) {
+                                unlock_page(page);
+                                page_cache_release(page);
+                                goto again;
+                        }
                 }
 
                 if (!PageUptodate(page)) {
@@ -926,15 +938,6 @@ again:
                         }
                 }
 
-                isize = i_size_read(inode);
-                file_end = (isize - 1) >> PAGE_CACHE_SHIFT;
-                if (!isize || page->index > file_end) {
-                        /* whoops, we blew past eof, skip this page */
-                        unlock_page(page);
-                        page_cache_release(page);
-                        break;
-                }
-
                 if (page->mapping != inode->i_mapping) {
                         unlock_page(page);
                         page_cache_release(page);
@@ -967,12 +970,12 @@ again:
                           EXTENT_DO_ACCOUNTING, 0, 0, &cached_state,
                           GFP_NOFS);
 
-        if (i_done != num_pages) {
+        if (i_done != page_cnt) {
                 spin_lock(&BTRFS_I(inode)->lock);
                 BTRFS_I(inode)->outstanding_extents++;
                 spin_unlock(&BTRFS_I(inode)->lock);
                 btrfs_delalloc_release_space(inode,
-                                     (num_pages - i_done) << PAGE_CACHE_SHIFT);
+                                     (page_cnt - i_done) << PAGE_CACHE_SHIFT);
         }
 
 
@@ -997,7 +1000,7 @@ out:
                 unlock_page(pages[i]);
                 page_cache_release(pages[i]);
         }
-        btrfs_delalloc_release_space(inode, num_pages << PAGE_CACHE_SHIFT);
+        btrfs_delalloc_release_space(inode, page_cnt << PAGE_CACHE_SHIFT);
         return ret;
 
 }