Btrfs: fix fsync data loss after a ranged fsync

While we're doing a full fsync (when the inode has the flag
BTRFS_INODE_NEEDS_FULL_SYNC set) that is ranged too (covers only a
portion of the file), we might have ordered operations that are started
before or while we're logging the inode and that fall outside the fsync
range.

Therefore when a full ranged fsync finishes don't remove every extent
map from the list of modified extent maps - as for some of them, that
fall outside our fsync range, their respective ordered operation hasn't
finished yet, meaning the corresponding file extent item wasn't inserted
into the fs/subvol tree yet and therefore we didn't log it, and we must
let the next fast fsync (one that checks only the modified list) see this
extent map and log a matching file extent item to the log btree and wait
for its ordered operation to finish (if it's still ongoing).

A test case for xfstests follows.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

3 files changed, 64 insertions, 17 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 36861b7a6757..ff1cc0399b9a 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1966,7 +1966,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 
         btrfs_init_log_ctx(&ctx);
 
-        ret = btrfs_log_dentry_safe(trans, root, dentry, &ctx);
+        ret = btrfs_log_dentry_safe(trans, root, dentry, start, end, &ctx);
         if (ret < 0) {
                 /* Fallthrough and commit/free transaction. */
                 ret = 1;
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 7e0e6e3029dd..d296efe2d3e7 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -94,8 +94,10 @@
 #define LOG_WALK_REPLAY_ALL 3
 
 static int btrfs_log_inode(struct btrfs_trans_handle *trans,
-                             struct btrfs_root *root, struct inode *inode,
-                             int inode_only);
+                           struct btrfs_root *root, struct inode *inode,
+                           int inode_only,
+                           const loff_t start,
+                           const loff_t end);
 static int link_to_fixup_dir(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root,
                              struct btrfs_path *path, u64 objectid);
@@ -3858,8 +3860,10 @@ process:
  * This handles both files and directories.
  */
 static int btrfs_log_inode(struct btrfs_trans_handle *trans,
-                             struct btrfs_root *root, struct inode *inode,
-                             int inode_only)
+                           struct btrfs_root *root, struct inode *inode,
+                           int inode_only,
+                           const loff_t start,
+                           const loff_t end)
 {
         struct btrfs_path *path;
         struct btrfs_path *dst_path;
@@ -3876,6 +3880,7 @@ static int btrfs_log_inode(struct btrfs_trans_handle *trans,
         int ins_nr;
         bool fast_search = false;
         u64 ino = btrfs_ino(inode);
+        struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
 
         path = btrfs_alloc_path();
         if (!path)
@@ -4049,13 +4054,35 @@ log_extents:
                         goto out_unlock;
                 }
         } else if (inode_only == LOG_INODE_ALL) {
-                struct extent_map_tree *tree = &BTRFS_I(inode)->extent_tree;
                 struct extent_map *em, *n;
 
-                write_lock(&tree->lock);
-                list_for_each_entry_safe(em, n, &tree->modified_extents, list)
-                        list_del_init(&em->list);
-                write_unlock(&tree->lock);
+                write_lock(&em_tree->lock);
+                /*
+                 * We can't just remove every em if we're called for a ranged
+                 * fsync - that is, one that doesn't cover the whole possible
+                 * file range (0 to LLONG_MAX). This is because we can have
+                 * em's that fall outside the range we're logging and therefore
+                 * their ordered operations haven't completed yet
+                 * (btrfs_finish_ordered_io() not invoked yet). This means we
+                 * didn't get their respective file extent item in the fs/subvol
+                 * tree yet, and need to let the next fast fsync (one which
+                 * consults the list of modified extent maps) find the em so
+                 * that it logs a matching file extent item and waits for the
+                 * respective ordered operation to complete (if it's still
+                 * running).
+                 *
+                 * Removing every em outside the range we're logging would make
+                 * the next fast fsync not log their matching file extent items,
+                 * therefore making us lose data after a log replay.
+                 */
+                list_for_each_entry_safe(em, n, &em_tree->modified_extents,
+                                         list) {
+                        const u64 mod_end = em->mod_start + em->mod_len - 1;
+
+                        if (em->mod_start >= start && mod_end <= end)
+                                list_del_init(&em->list);
+                }
+                write_unlock(&em_tree->lock);
         }
 
         if (inode_only == LOG_INODE_ALL && S_ISDIR(inode->i_mode)) {
@@ -4065,8 +4092,19 @@ log_extents:
                         goto out_unlock;
                 }
         }
-        BTRFS_I(inode)->logged_trans = trans->transid;
-        BTRFS_I(inode)->last_log_commit = BTRFS_I(inode)->last_sub_trans;
+
+        write_lock(&em_tree->lock);
+        /*
+         * If we're doing a ranged fsync and there are still modified extents
+         * in the list, we must run on the next fsync call as it might cover
+         * those extents (a full fsync or an fsync for other range).
+         */
+        if (list_empty(&em_tree->modified_extents)) {
+                BTRFS_I(inode)->logged_trans = trans->transid;
+                BTRFS_I(inode)->last_log_commit =
+                        BTRFS_I(inode)->last_sub_trans;
+        }
+        write_unlock(&em_tree->lock);
 out_unlock:
         if (unlikely(err))
                 btrfs_put_logged_extents(&logged_list);
@@ -4161,7 +4199,10 @@ out:
  */
 static int btrfs_log_inode_parent(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root, struct inode *inode,
-                                  struct dentry *parent, int exists_only,
+                                  struct dentry *parent,
+                                  const loff_t start,
+                                  const loff_t end,
+                                  int exists_only,
                                   struct btrfs_log_ctx *ctx)
 {
         int inode_only = exists_only ? LOG_INODE_EXISTS : LOG_INODE_ALL;
@@ -4207,7 +4248,7 @@ static int btrfs_log_inode_parent(struct btrfs_trans_handle *trans,
         if (ret)
                 goto end_no_trans;
 
-        ret = btrfs_log_inode(trans, root, inode, inode_only);
+        ret = btrfs_log_inode(trans, root, inode, inode_only, start, end);
         if (ret)
                 goto end_trans;
 
@@ -4235,7 +4276,8 @@ static int btrfs_log_inode_parent(struct btrfs_trans_handle *trans,
 
                 if (BTRFS_I(inode)->generation >
                     root->fs_info->last_trans_committed) {
-                        ret = btrfs_log_inode(trans, root, inode, inode_only);
+                        ret = btrfs_log_inode(trans, root, inode, inode_only,
+                                              0, LLONG_MAX);
                         if (ret)
                                 goto end_trans;
                 }
@@ -4269,13 +4311,15 @@ end_no_trans:
  */
 int btrfs_log_dentry_safe(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root, struct dentry *dentry,
+                          const loff_t start,
+                          const loff_t end,
                           struct btrfs_log_ctx *ctx)
 {
         struct dentry *parent = dget_parent(dentry);
         int ret;
 
         ret = btrfs_log_inode_parent(trans, root, dentry->d_inode, parent,
-                                     0, ctx);
+                                     start, end, 0, ctx);
         dput(parent);
 
         return ret;
@@ -4512,6 +4556,7 @@ int btrfs_log_new_name(struct btrfs_trans_handle *trans,
                     root->fs_info->last_trans_committed))
                 return 0;
 
-        return btrfs_log_inode_parent(trans, root, inode, parent, 1, NULL);
+        return btrfs_log_inode_parent(trans, root, inode, parent, 0,
+                                      LLONG_MAX, 1, NULL);
 }
 
diff --git a/fs/btrfs/tree-log.h b/fs/btrfs/tree-log.h
index 7f5b41bd5373..e2e798ae7cd7 100644
--- a/fs/btrfs/tree-log.h
+++ b/fs/btrfs/tree-log.h
@@ -59,6 +59,8 @@ int btrfs_free_log_root_tree(struct btrfs_trans_handle *trans,
 int btrfs_recover_log_trees(struct btrfs_root *tree_root);
 int btrfs_log_dentry_safe(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root, struct dentry *dentry,
+                          const loff_t start,
+                          const loff_t end,
                           struct btrfs_log_ctx *ctx);
 int btrfs_del_dir_entries_in_log(struct btrfs_trans_handle *trans,
                                  struct btrfs_root *root,