target: Fix PR registration + APTPL RCU conversion regression

This patch fixes a v4.2+ regression introduced by commit 79dc9c9e86
where lookup of t10_pr_registration->pr_reg_deve and associated
->pr_kref get was missing from __core_scsi3_do_alloc_registration(),
which is responsible for setting DEF_PR_REG_ACTIVE.

This would result in REGISTER operations completing successfully,
but subsequent core_scsi3_pr_seq_non_holder() checking would fail
with !DEF_PR_REG_ACTIVE -> RESERVATION CONFLICT status.

Update __core_scsi3_add_registration() to drop ->pr_kref reference
after registration and any optional ALL_TG_PT=1 processing has
completed.  Update core_scsi3_decode_spec_i_port() to release
the new parent local_pr_reg->pr_kref as well.

Also, update __core_scsi3_check_aptpl_registration() to perform
the same target_nacl_find_deve() lookup + ->pr_kref get, now that
__core_scsi3_add_registration() expects to drop the reference.

Finally, since there are cases when se_dev_entry->se_lun_acl can
still be dereferenced in core_scsi3_lunacl_undepend_item() while
holding ->pr_kref, go ahead and move explicit rcu_assign_pointer()
NULL assignments within core_disable_device_list_for_node() until
after orig->pr_comp finishes.

Reported-by: Scott L. Lykens <scott@lykens.org>
Tested-by: Scott L. Lykens <scott@lykens.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Lee Duncan <lduncan@suse.com>
Cc: <stable@vger.kernel.org> # v4.2+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
index dcc424ac35d4..abf20763b0b6 100644
--- a/drivers/target/target_core_device.c
+++ b/drivers/target/target_core_device.c
@@ -427,8 +427,6 @@ void core_disable_device_list_for_node(
 
 	hlist_del_rcu(&orig->link);
 	clear_bit(DEF_PR_REG_ACTIVE, &orig->deve_flags);
-	rcu_assign_pointer(orig->se_lun, NULL);
-	rcu_assign_pointer(orig->se_lun_acl, NULL);
 	orig->lun_flags = 0;
 	orig->creation_time = 0;
 	orig->attach_count--;
@@ -439,6 +437,9 @@ void core_disable_device_list_for_node(
 	kref_put(&orig->pr_kref, target_pr_kref_release);
 	wait_for_completion(&orig->pr_comp);
 
+	rcu_assign_pointer(orig->se_lun, NULL);
+	rcu_assign_pointer(orig->se_lun_acl, NULL);
+
 	kfree_rcu(orig, rcu_head);
 
 	core_scsi3_free_pr_reg_from_nacl(dev, nacl);