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btrfs: Fix busyloops in transaction waiting code

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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>
This commit is contained in:
Jan Kara 2012-01-26 15:01:11 -05:00 committed by Chris Mason
parent 357b9784b7
commit 6dd70ce4eb
1 changed files with 4 additions and 2 deletions
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6
fs/btrfs/tree-log.c
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@ -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);