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quota: Do not acquire dqio_sem for dquot overwrites in v2 format 

When dquot has space already allocated in a quota file, we just
overwrite that place when writing dquot. So we don't need any protection
against other modifications of quota file as these keep dquot in place.

Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Jan Kara 2017-06-08 16:09:46 +02:00
parent 8fc32c2b0d
commit d2faa41516
1 changed files with 13 additions and 2 deletions
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15
fs/quota/quota_v2.c
View File

@ -300,12 +300,23 @@ static int v2_write_dquot(struct dquot *dquot)
{
struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
int ret;
bool alloc = false;
down_write(&dqopt->dqio_sem);
/*
* If space for dquot is already allocated, we don't need any
* protection as we'll only overwrite the place of dquot. We are
* still protected by concurrent writes of the same dquot by
* dquot->dq_lock.
*/
if (!dquot->dq_off) {
alloc = true;
down_write(&dqopt->dqio_sem);
}
ret = qtree_write_dquot(
sb_dqinfo(dquot->dq_sb, dquot->dq_id.type)->dqi_priv,
dquot);
up_write(&dqopt->dqio_sem);
if (alloc)
up_write(&dqopt->dqio_sem);
return ret;
}