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

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

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index c9ebd4fe8f7ee3d39d4afa06ac70721ecedfc357..e862292bdfc61d163353b6b5ed976beb4e913a86 100644 (file)
--- 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])