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>

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 9e097fbfc78d395dca4e461f5a054135aa4e1ba3..b0ff34b966078e0ef5221cac40678b2c725b026a 100644 (file)
--- 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)