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btrfs: Remove unnecessary check from join_running_log_trans

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join_running_log_trans checks btrfs_root::log_root outside of
btrfs_root::log_mutex to avoid contention on the mutex. Turns out this
check is not necessary because the two callers of join_running_log_trans
(both of which deal with removing entries from the tree-log during
unlink) explicitly check whether the respective inode has been logged in
the current transaction.

If it hasn't then it won't have any items in the tree-log and call path
will return before calling join_running_log_trans. If the check passes,
however, then it's guaranteed that btrfs_root::log_root is set because
the inode is logged.

Those guarantees allows us to remove the speculative as well as the
implicity and tricky memory barrier.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Nikolay Borisov 2019-05-23 14:51:26 +03:00 committed by David Sterba
parent 32e534402a
commit e678934cbe
1 changed files with 0 additions and 4 deletions
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4
fs/btrfs/tree-log.c
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@ -188,10 +188,6 @@ static int join_running_log_trans(struct btrfs_root *root)
{
int ret = -ENOENT;
smp_mb();
if (!root->log_root)
return -ENOENT;
mutex_lock(&root->log_mutex);
if (root->log_root) {
ret = 0;