On Sun, Jan 28, 2018 at 11:17:20AM +0200, Leon Romanovsky wrote:
> +int __must_check rdma_restrack_get(struct rdma_restrack_entry *res)
> +{
> + return kref_get_unless_zero(&res->kref);
> +}
> +EXPORT_SYMBOL(rdma_restrack_get);
> +
> +static void restrack_release(struct kref *kref)
> +{
> + struct rdma_restrack_entry *res;
> +
> + res = container_of(kref, struct rdma_restrack_entry, kref);
> + complete(&res->comp);
> +}
> +
> +int rdma_restrack_put(struct rdma_restrack_entry *res)
> +{
> + return kref_put(&res->kref, restrack_release);
> +}
> +EXPORT_SYMBOL(rdma_restrack_put);
> +
> +void rdma_restrack_del(struct rdma_restrack_entry *res)
> +{
> + struct ib_device *dev;
> +
> + if (!res->valid)
> + return;
> +
> + dev = res_to_dev(res);
> + if (!dev)
> + return;
> +
> + down_read(&dev->res.rwsem);
> + rdma_restrack_put(res);
> + up_read(&dev->res.rwsem);
I can't see why this lock is necessary, the underlying kref is already
atomic.
This locking seems fine, can't see any problem with it.
But I still hate the readability of the kref-as-not-a-kref approach.
Now that you've written it out, it is clear this is actually open
coding a rw_semaphore??
I think lockdep will be okay with this due to the trylock?
It saves a bit of memory compared to a kref + completion, and has
better clarity:
static inline int __must_check rdma_restrack_get(struct rdma_restrack_entry *res)
{
return down_read_trylock(&res->rwsem);
}
static inline int rdma_restrack_put(struct rdma_restrack_entry *res)
{
return up_read(&res->rwsem);
}
void rdma_restrack_del(struct rdma_restrack_entry *res)
{
down_write(res->rwsem);
down_write(&dev->res.rwsem);
hash_del(&res->node);
[..]
}
No change to the read side.
Jason
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