Btrfs: Fix lock ordering of the snapshot semaphore against the page lock

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index c9ebd4fe8f7e..e862292bdfc6 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -251,7 +251,6 @@ static int noinline dirty_and_release_pages(struct btrfs_trans_handle *trans,
         num_bytes = (write_bytes + pos - start_pos +
                     root->sectorsize - 1) & ~((u64)root->sectorsize - 1);
 
-        down_read(&BTRFS_I(inode)->root->snap_sem);
         end_of_last_block = start_pos + num_bytes - 1;
 
         lock_extent(em_tree, start_pos, end_of_last_block, GFP_NOFS);
@@ -356,7 +355,6 @@ out_unlock:
         mutex_unlock(&root->fs_info->fs_mutex);
         unlock_extent(em_tree, start_pos, end_of_last_block, GFP_NOFS);
         free_extent_map(em);
-        up_read(&BTRFS_I(inode)->root->snap_sem);
         return err;
 }
 
@@ -726,6 +724,8 @@ static ssize_t btrfs_file_write(struct file *file, const char __user *buf,
 
         pages = kmalloc(nrptrs * sizeof(struct page *), GFP_KERNEL);
 
+        down_read(&BTRFS_I(inode)->root->snap_sem);
+
         mutex_lock(&inode->i_mutex);
         first_index = pos >> PAGE_CACHE_SHIFT;
         last_index = (pos + count) >> PAGE_CACHE_SHIFT;
@@ -804,6 +804,8 @@ static ssize_t btrfs_file_write(struct file *file, const char __user *buf,
         }
 out:
         mutex_unlock(&inode->i_mutex);
+        up_read(&BTRFS_I(inode)->root->snap_sem);
+
 out_nolock:
         kfree(pages);
         if (pinned[0])