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-rw-r--r--fs/btrfs/file.c56
1 files changed, 28 insertions, 28 deletions
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index b476e5645034..6351947c9bb0 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1811,22 +1811,10 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
mutex_unlock(&inode->i_mutex);
/*
- * we want to make sure fsync finds this change
- * but we haven't joined a transaction running right now.
- *
- * Later on, someone is sure to update the inode and get the
- * real transid recorded.
- *
- * We set last_trans now to the fs_info generation + 1,
- * this will either be one more than the running transaction
- * or the generation used for the next transaction if there isn't
- * one running right now.
- *
* We also have to set last_sub_trans to the current log transid,
* otherwise subsequent syncs to a file that's been synced in this
* transaction will appear to have already occured.
*/
- BTRFS_I(inode)->last_trans = root->fs_info->generation + 1;
BTRFS_I(inode)->last_sub_trans = root->log_transid;
if (num_written > 0) {
err = generic_write_sync(file, pos, num_written);
@@ -1959,25 +1947,37 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
atomic_inc(&root->log_batch);
/*
- * check the transaction that last modified this inode
- * and see if its already been committed
- */
- if (!BTRFS_I(inode)->last_trans) {
- mutex_unlock(&inode->i_mutex);
- goto out;
- }
-
- /*
- * if the last transaction that changed this file was before
- * the current transaction, we can bail out now without any
- * syncing
+ * If the last transaction that changed this file was before the current
+ * transaction and we have the full sync flag set in our inode, we can
+ * bail out now without any syncing.
+ *
+ * Note that we can't bail out if the full sync flag isn't set. This is
+ * because when the full sync flag is set we start all ordered extents
+ * and wait for them to fully complete - when they complete they update
+ * the inode's last_trans field through:
+ *
+ * btrfs_finish_ordered_io() ->
+ * btrfs_update_inode_fallback() ->
+ * btrfs_update_inode() ->
+ * btrfs_set_inode_last_trans()
+ *
+ * So we are sure that last_trans is up to date and can do this check to
+ * bail out safely. For the fast path, when the full sync flag is not
+ * set in our inode, we can not do it because we start only our ordered
+ * extents and don't wait for them to complete (that is when
+ * btrfs_finish_ordered_io runs), so here at this point their last_trans
+ * value might be less than or equals to fs_info->last_trans_committed,
+ * and setting a speculative last_trans for an inode when a buffered
+ * write is made (such as fs_info->generation + 1 for example) would not
+ * be reliable since after setting the value and before fsync is called
+ * any number of transactions can start and commit (transaction kthread
+ * commits the current transaction periodically), and a transaction
+ * commit does not start nor waits for ordered extents to complete.
*/
smp_mb();
if (btrfs_inode_in_log(inode, root->fs_info->generation) ||
- BTRFS_I(inode)->last_trans <=
- root->fs_info->last_trans_committed) {
- BTRFS_I(inode)->last_trans = 0;
-
+ (full_sync && BTRFS_I(inode)->last_trans <=
+ root->fs_info->last_trans_committed)) {
/*
* We'v had everything committed since the last time we were
* modified so clear this flag in case it was set for whatever