Btrfs: Fix page count calculation

take offset of start position into account when calculating page count.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 9e097fbfc78d..b0ff34b96607 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -991,8 +991,8 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
                 size_t write_bytes = min(iov_iter_count(&i),
                                          nrptrs * (size_t)PAGE_CACHE_SIZE -
                                          offset);
-                size_t num_pages = (write_bytes + PAGE_CACHE_SIZE - 1) >>
-                                        PAGE_CACHE_SHIFT;
+                size_t num_pages = (write_bytes + offset +
+                                    PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 
                 WARN_ON(num_pages > nrptrs);
                 memset(pages, 0, sizeof(struct page *) * nrptrs);
@@ -1022,8 +1022,8 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 
                 copied = btrfs_copy_from_user(pos, num_pages,
                                            write_bytes, pages, &i);
-                dirty_pages = (copied + PAGE_CACHE_SIZE - 1) >>
-                                        PAGE_CACHE_SHIFT;
+                dirty_pages = (copied + offset + PAGE_CACHE_SIZE - 1) >>
+                                PAGE_CACHE_SHIFT;
 
                 if (num_pages > dirty_pages) {
                         if (copied > 0)