Re: [PATCH 4/6] shmem: prepare shmem quota infrastructure

[Jan Kara <jack@suse.cz>]

On Mon 03-04-23 10:47:57, cem@kernel.org wrote:
> From: Lukas Czerner <lczerner@redhat.com>
> 
> Add new shmem quota format, its quota_format_ops together with
> dquot_operations
> 
> Signed-off-by: Lukas Czerner <lczerner@redhat.com>
> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>

Just two small things below.

> diff --git a/mm/shmem_quota.c b/mm/shmem_quota.c
> new file mode 100644
> index 0000000000000..c415043a71e67
> --- /dev/null
> +++ b/mm/shmem_quota.c
...
> +/*
> + * Load dquot with limits from existing entry, or create the new entry if
> + * it does not exist.
> + */
> +static int shmem_acquire_dquot(struct dquot *dquot)
> +{
> +	struct mem_dqinfo *info = sb_dqinfo(dquot->dq_sb, dquot->dq_id.type);
> +	struct rb_node **n = &((struct rb_root *)info->dqi_priv)->rb_node;
> +	struct rb_node *parent = NULL, *new_node = NULL;
> +	struct quota_id *new_entry, *entry;
> +	qid_t id = from_kqid(&init_user_ns, dquot->dq_id);
> +	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
> +	int ret = 0;
> +
> +	mutex_lock(&dquot->dq_lock);
> +
> +	down_write(&dqopt->dqio_sem);
> +	while (*n) {
> +		parent = *n;
> +		entry = rb_entry(parent, struct quota_id, node);
> +
> +		if (id < entry->id)
> +			n = &(*n)->rb_left;
> +		else if (id > entry->id)
> +			n = &(*n)->rb_right;
> +		else
> +			goto found;
> +	}
> +
> +	/* We don't have entry for this id yet, create it */
> +	new_entry = kzalloc(sizeof(struct quota_id), GFP_NOFS);
> +	if (!new_entry) {
> +		ret = -ENOMEM;
> +		goto out_unlock;
> +	}
> +
> +	new_entry->id = id;
> +	new_node = &new_entry->node;
> +	rb_link_node(new_node, parent, n);
> +	rb_insert_color(new_node, (struct rb_root *)info->dqi_priv);
> +	entry = new_entry;
> +
> +found:
> +	/* Load the stored limits from the tree */
> +	spin_lock(&dquot->dq_dqb_lock);
> +	dquot->dq_dqb.dqb_bhardlimit = entry->bhardlimit;
> +	dquot->dq_dqb.dqb_bsoftlimit = entry->bsoftlimit;
> +	dquot->dq_dqb.dqb_ihardlimit = entry->ihardlimit;
> +	dquot->dq_dqb.dqb_isoftlimit = entry->isoftlimit;
> +
> +	if (!dquot->dq_dqb.dqb_bhardlimit &&
> +	    !dquot->dq_dqb.dqb_bsoftlimit &&
> +	    !dquot->dq_dqb.dqb_ihardlimit &&
> +	    !dquot->dq_dqb.dqb_isoftlimit)
> +		set_bit(DQ_FAKE_B, &dquot->dq_flags);
> +	spin_unlock(&dquot->dq_dqb_lock);
> +
> +	/* Make sure flags update is visible after dquot has been filled */
> +	smp_mb__before_atomic();
> +	set_bit(DQ_ACTIVE_B, &dquot->dq_flags);

I'm slightly wondering whether we shouldn't have a dquot_mark_active()
helper for this to hide the barrier details...

> +out_unlock:
> +	up_write(&dqopt->dqio_sem);
> +	mutex_unlock(&dquot->dq_lock);
> +	return ret;
> +}
> +
> +/*
> + * Store limits from dquot in the tree unless it's fake. If it is fake
> + * remove the id from the tree since there is no useful information in
> + * there.
> + */
> +static int shmem_release_dquot(struct dquot *dquot)
> +{
> +	struct mem_dqinfo *info = sb_dqinfo(dquot->dq_sb, dquot->dq_id.type);
> +	struct rb_node *node = ((struct rb_root *)info->dqi_priv)->rb_node;
> +	qid_t id = from_kqid(&init_user_ns, dquot->dq_id);
> +	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
> +	struct quota_id *entry = NULL;
> +
> +	mutex_lock(&dquot->dq_lock);
> +	/* Check whether we are not racing with some other dqget() */
> +	if (dquot_is_busy(dquot))
> +		goto out_dqlock;
> +
> +	down_write(&dqopt->dqio_sem);
> +	while (node) {
> +		entry = rb_entry(node, struct quota_id, node);
> +
> +		if (id < entry->id)
> +			node = node->rb_left;
> +		else if (id > entry->id)
> +			node = node->rb_right;
> +		else
> +			goto found;
> +	}
> +
> +	up_write(&dqopt->dqio_sem);
> +	mutex_unlock(&dquot->dq_lock);

We should report some kind of error here, shouldn't we? We do expect to
have the quota_id allocated from shmem_acquire_dquot() and we will be
possibly loosing set limits here.

Otherwise the patch looks good to me.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR