Btrfs: Fix bookend extent race v2

When dropping middle part of an extent, btrfs_drop_extents truncates
the extent at first, then inserts a bookend extent.

Since truncation and insertion can't be done atomically, there is a small
period that the bookend extent isn't in the tree. This causes problem for
functions that search the tree for file extent item. The way to fix this is
lock the range of the bookend extent before truncation.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>

1 files changed, 13 insertions, 15 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index fada9c22a021..535cee47fcfb 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3379,11 +3379,13 @@ static int noinline relocate_data_extent(struct inode *reloc_inode,
         struct btrfs_root *root = BTRFS_I(reloc_inode)->root;
         struct extent_map_tree *em_tree = &BTRFS_I(reloc_inode)->extent_tree;
         struct extent_map *em;
+        u64 start = extent_key->objectid - offset;
+        u64 end = start + extent_key->offset - 1;
 
         em = alloc_extent_map(GFP_NOFS);
         BUG_ON(!em || IS_ERR(em));
 
-        em->start = extent_key->objectid - offset;
+        em->start = start;
         em->len = extent_key->offset;
         em->block_len = extent_key->offset;
         em->block_start = extent_key->objectid;
@@ -3391,7 +3393,7 @@ static int noinline relocate_data_extent(struct inode *reloc_inode,
         set_bit(EXTENT_FLAG_PINNED, &em->flags);
 
         /* setup extent map to cheat btrfs_readpage */
-        mutex_lock(&BTRFS_I(reloc_inode)->extent_mutex);
+        lock_extent(&BTRFS_I(reloc_inode)->io_tree, start, end, GFP_NOFS);
         while (1) {
                 int ret;
                 spin_lock(&em_tree->lock);
@@ -3401,13 +3403,11 @@ static int noinline relocate_data_extent(struct inode *reloc_inode,
                         free_extent_map(em);
                         break;
                 }
-                btrfs_drop_extent_cache(reloc_inode, em->start,
-                                        em->start + em->len - 1, 0);
+                btrfs_drop_extent_cache(reloc_inode, start, end, 0);
         }
-        mutex_unlock(&BTRFS_I(reloc_inode)->extent_mutex);
+        unlock_extent(&BTRFS_I(reloc_inode)->io_tree, start, end, GFP_NOFS);
 
-        return relocate_inode_pages(reloc_inode, extent_key->objectid - offset,
-                                    extent_key->offset);
+        return relocate_inode_pages(reloc_inode, start, extent_key->offset);
 }
 
 struct btrfs_ref_path {
@@ -3831,7 +3831,6 @@ next:
                          * the file extent item was modified by someone
                          * before the extent got locked.
                          */
-                        mutex_unlock(&BTRFS_I(inode)->extent_mutex);
                         unlock_extent(&BTRFS_I(inode)->io_tree, lock_start,
                                       lock_end, GFP_NOFS);
                         extent_locked = 0;
@@ -3896,8 +3895,12 @@ next:
                         lock_start = key.offset;
                         lock_end = lock_start + num_bytes - 1;
                 } else {
-                        BUG_ON(lock_start != key.offset);
-                        BUG_ON(lock_end - lock_start + 1 < num_bytes);
+                        if (lock_start > key.offset ||
+                            lock_end + 1 < key.offset + num_bytes) {
+                                unlock_extent(&BTRFS_I(inode)->io_tree,
+                                              lock_start, lock_end, GFP_NOFS);
+                                extent_locked = 0;
+                        }
                 }
 
                 if (!inode) {
@@ -3951,7 +3954,6 @@ next:
                         if (ordered)
                                 btrfs_put_ordered_extent(ordered);
 
-                        mutex_lock(&BTRFS_I(inode)->extent_mutex);
                         extent_locked = 1;
                         continue;
                 }
@@ -4073,7 +4075,6 @@ next:
                 }
 
                 if (extent_locked) {
-                        mutex_unlock(&BTRFS_I(inode)->extent_mutex);
                         unlock_extent(&BTRFS_I(inode)->io_tree, lock_start,
                                       lock_end, GFP_NOFS);
                         extent_locked = 0;
@@ -4091,7 +4092,6 @@ out:
         if (inode) {
                 mutex_unlock(&inode->i_mutex);
                 if (extent_locked) {
-                        mutex_unlock(&BTRFS_I(inode)->extent_mutex);
                         unlock_extent(&BTRFS_I(inode)->io_tree, lock_start,
                                       lock_end, GFP_NOFS);
                 }
@@ -4180,10 +4180,8 @@ static int noinline invalidate_extent_cache(struct btrfs_root *root,
 
                 lock_extent(&BTRFS_I(inode)->io_tree, key.offset,
                             key.offset + num_bytes - 1, GFP_NOFS);
-                mutex_lock(&BTRFS_I(inode)->extent_mutex);
                 btrfs_drop_extent_cache(inode, key.offset,
                                         key.offset + num_bytes - 1, 1);
-                mutex_unlock(&BTRFS_I(inode)->extent_mutex);
                 unlock_extent(&BTRFS_I(inode)->io_tree, key.offset,
                               key.offset + num_bytes - 1, GFP_NOFS);
                 cond_resched();