On Aug 16, 2017, at 9:41 AM, Jan Kara <jack@xxxxxxx> wrote:
>
> 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.
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
> ---
> fs/quota/quota_v2.c | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/fs/quota/quota_v2.c b/fs/quota/quota_v2.c
> index 482733abe4ac..7a05b80f3b8c 100644
> --- a/fs/quota/quota_v2.c
> +++ b/fs/quota/quota_v2.c
> @@ -300,12 +300,23 @@ static int v2_write_dquot(struct dquot *dquot)
> {
> struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
> int ret;
> -
> - down_write(&dqopt->dqio_sem);
> + bool alloc = false;
> +
> + /*
> + * 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;
> }
>
> --
> 2.12.3
>
Cheers, Andreas
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