btrfs: Fix busyloops in transaction waiting code (6dd70ce4) · Commits · 戴 / test

wait_log_commit() and wait_for_writer() were using slightly different conditions for deciding whether they should call schedule() and whether they should continue in the wait loop. Thus it could happen that we busylooped when the first condition was not true while the second one was. That is burning CPU cycles needlessly and is deadly on UP machines... Signed-off-by:

Jan Kara <jack@suse.cz> Signed-off-by:

Chris Mason <chris.mason@oracle.com>

fs/btrfs/tree-log.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -1957,7 +1957,8 @@ static int wait_log_commit(struct btrfs_trans_handle *trans,

		finish_wait(&root->log_commit_wait[index], &wait);
		mutex_lock(&root->log_mutex);
		} while (root->log_transid < transid + 2 &&
		} while (root->fs_info->last_trans_log_full_commit !=
		trans->transid && root->log_transid < transid + 2 &&
		atomic_read(&root->log_commit[index]));
		return 0;
		}
		@@ -1966,7 +1967,8 @@ static int wait_for_writer(struct btrfs_trans_handle *trans,
		struct btrfs_root *root)
		{
		DEFINE_WAIT(wait);
		while (atomic_read(&root->log_writers)) {
		while (root->fs_info->last_trans_log_full_commit !=
		trans->transid && atomic_read(&root->log_writers)) {
		prepare_to_wait(&root->log_writer_wait,
		&wait, TASK_UNINTERRUPTIBLE);
		mutex_unlock(&root->log_mutex);

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