On Thu, Oct 24, 2013 at 02:30:19PM -0400, Mike Snitzer wrote:
> From: Heinz Mauelshagen <heinzm@xxxxxxxxxx>
> Addresses callers' (insert_in*cache()) requirement that alloc_entry()
> return NULL when an entry isn't able to be allocated.
What is the code path that leads to the requirement for this patch?
> +++ b/drivers/md/dm-cache-policy-mq.c
> static struct entry *alloc_entry(struct mq_policy *mq)
> + struct entry *e = NULL;
>
> if (mq->nr_entries_allocated >= mq->nr_entries) {
> BUG_ON(!list_empty(&mq->free));
> return NULL;
> }
>
> - e = list_entry(list_pop(&mq->free), struct entry, list);
> - INIT_LIST_HEAD(&e->list);
> - INIT_HLIST_NODE(&e->hlist);
> + if (!list_empty(&mq->free)) {
> + e = list_entry(list_pop(&mq->free), struct entry, list);
> + INIT_LIST_HEAD(&e->list);
> + INIT_HLIST_NODE(&e->hlist);
> + mq->nr_entries_allocated++;
> + }
In other words, under what circumstances is mq->nr_entries_allocated
less then mq->nr_entries, yet the mq->free list is empty?
Is it better to apply a patch like this, or rather to fix whatever situation
leads to those circumstances? Has the bug/race always been there or is it a
regression?
Alasdair
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