Re: [PATCH-v2 1/9] target: Convert se_node_acl->device_list[] to RCU hlist

Christoph Hellwig
2015-05-22T08:24:16Z

> - spin_lock_irqsave(&se_sess->se_node_acl->device_list_lock, flags);
> - se_cmd->se_deve = se_sess->se_node_acl->device_list[unpacked_lun];
> - if (se_cmd->se_deve->lun_flags & TRANSPORT_LUNFLAGS_INITIATOR_ACCESS) {
> - struct se_dev_entry *deve = se_cmd->se_deve;
> -
> + rcu_read_lock();
> + deve = target_nacl_find_deve(nacl, unpacked_lun);
> + if (deve) {
> deve->total_cmds++;

This update will now be racy, ditto for the read/write_bytes update
later.

> +bool target_lun_is_rdonly(struct se_cmd *cmd)
> +{
> + struct se_session *se_sess = cmd->se_sess;
> + struct se_dev_entry *deve;
> + bool ret;
> +
> + if (cmd->se_lun->lun_access & TRANSPORT_LUNFLAGS_READ_ONLY)
> + return true;
> +
> + rcu_read_lock();
> + deve = target_nacl_find_deve(se_sess->se_node_acl, cmd->orig_fe_lun);
> + ret = (deve && deve->lun_flags & TRANSPORT_LUNFLAGS_READ_ONLY);
> + rcu_read_unlock();
> +
> + return ret;
> +}
> +EXPORT_SYMBOL(target_lun_is_rdonly);

This should be a separate prep patch like, like it was in my original
version. I also still think you want this whole patch:

http://git.infradead.org/users/hch/scsi.git/commitdiff/e9a71bda1a120e0488c5c4e4b2f17f14333e2dc6

as storing a pointer to the dev entry without a refcount is bound to
cause trouble. I don't have a tree with all the patches applied
available, but I doubt it fully gets that right.

> +void target_pr_kref_release(struct kref *kref)
> +{
> + struct se_dev_entry *deve = container_of(kref, struct se_dev_entry,
> + pr_kref);
> + complete(&deve->pr_comp);
> }
>
> /* core_enable_device_list_for_node():

> + kref_put(&orig->pr_kref, target_pr_kref_release);
> + wait_for_completion(&orig->pr_comp);
>

> + kref_put(&orig->pr_kref, target_pr_kref_release);
> /*
> - * Disable struct se_dev_entry LUN ACL mapping
> + * Before fireing off RCU callback, wait for any in process SPEC_I_PT=1
> + * or REGISTER_AND_MOVE PR operation to complete.
> */
> + wait_for_completion(&orig->pr_comp);
> + kfree_rcu(orig, rcu_head);

The release callback should just call kfree_rcu, no need to wait for the
release in the caller.

Also can you drop the _pr from the name? It's a generic refcount now
even if the PR code is the only consumer so far.

> +void target_pr_kref_release(struct kref *);

Instead of exporting the release function it would be much more obvious
to have a

void target_deve_put(struct se_dev_entry *deve)
{
kref_put(&deve->pr_kref, target_deve_release);
}

helper. Probably paired with one for the get side.

> static void core_scsi3_lunacl_undepend_item(struct se_dev_entry *se_deve)
> {
> - struct se_lun_acl *lun_acl = se_deve->se_lun_acl;
> + struct se_lun_acl *lun_acl;
> struct se_node_acl *nacl;
> struct se_portal_group *tpg;
> +
> + if (!se_deve) {
> + pr_err("core_scsi3_lunacl_undepend_item passed NULL se_deve\n");
> + dump_stack();
> + return;
> + }

How could this happen and how is it related to this patch?

> - if (!deve->se_lun || !deve->se_lun_acl) {
> - spin_unlock_irq(&nacl->device_list_lock);
> + rcu_read_lock();
> + deve = target_nacl_find_deve(nacl, lacl->mapped_lun);
> + if (!deve) {
> + rcu_read_unlock();
> return -ENODEV;

So previously a lot of these files returned -ENODEV when not having
an explicit node ACL, and now they don't. If that was intentional
it should be documented in the changelog, or preferably moved into
a preparation patch of its own.

> + struct se_node_acl *se_node_acl;

Where is this field coming from? It's not documented in the changelog
and doesn't seem to be actually used either.