scsi: target/core: Simplify transport_clear_lun_ref()

Since transport_clear_lun_ref() already waits until the percpu-refcount
.release() method is called, it is not necessary to wait first until
percpu_ref_kill_and_confirm() has finished transitioning the refcount into
atomic mode. Remove the code that waits for percpu_ref_kill_and_confirm()
to complete and also the completion object that is used by that code.  This
patch does not change the behavior of the SCSI target code.

Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: Mike Christie <mchristi@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Disseldorp <ddiss@suse.de>
Cc: Hannes Reinecke <hare@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

3 files changed, 5 insertions, 32 deletions

diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
index cffd7430bb99..1d51df2b3e77 100644
--- a/drivers/target/target_core_device.c
+++ b/drivers/target/target_core_device.c
@@ -823,7 +823,6 @@ struct se_device *target_alloc_device(struct se_hba *hba, const char *name)
 
         xcopy_lun = &dev->xcopy_lun;
         rcu_assign_pointer(xcopy_lun->lun_se_dev, dev);
-        init_completion(&xcopy_lun->lun_ref_comp);
         init_completion(&xcopy_lun->lun_shutdown_comp);
         INIT_LIST_HEAD(&xcopy_lun->lun_deve_list);
         INIT_LIST_HEAD(&xcopy_lun->lun_dev_link);
diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index 16e7a6500be4..e2ace1059437 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -577,7 +577,6 @@ struct se_lun *core_tpg_alloc_lun(
         }
         lun->unpacked_lun = unpacked_lun;
         atomic_set(&lun->lun_acl_count, 0);
-        init_completion(&lun->lun_ref_comp);
         init_completion(&lun->lun_shutdown_comp);
         INIT_LIST_HEAD(&lun->lun_deve_list);
         INIT_LIST_HEAD(&lun->lun_dev_link);
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 4d1651e46ea9..0c8eca6ae30f 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -2911,38 +2911,13 @@ void target_wait_for_sess_cmds(struct se_session *se_sess)
 }
 EXPORT_SYMBOL(target_wait_for_sess_cmds);
 
-static void target_lun_confirm(struct percpu_ref *ref)
-{
-        struct se_lun *lun = container_of(ref, struct se_lun, lun_ref);
-
-        complete(&lun->lun_ref_comp);
-}
-
+/*
+ * Prevent that new percpu_ref_tryget_live() calls succeed and wait until
+ * all references to the LUN have been released. Called during LUN shutdown.
+ */
 void transport_clear_lun_ref(struct se_lun *lun)
 {
-        /*
-         * Mark the percpu-ref as DEAD, switch to atomic_t mode, drop
-         * the initial reference and schedule confirm kill to be
-         * executed after one full RCU grace period has completed.
-         */
-        percpu_ref_kill_and_confirm(&lun->lun_ref, target_lun_confirm);
-        /*
-         * The first completion waits for percpu_ref_switch_to_atomic_rcu()
-         * to call target_lun_confirm after lun->lun_ref has been marked
-         * as __PERCPU_REF_DEAD on all CPUs, and switches to atomic_t
-         * mode so that percpu_ref_tryget_live() lookup of lun->lun_ref
-         * fails for all new incoming I/O.
-         */
-        wait_for_completion(&lun->lun_ref_comp);
-        /*
-         * The second completion waits for percpu_ref_put_many() to
-         * invoke ->release() after lun->lun_ref has switched to
-         * atomic_t mode, and lun->lun_ref.count has reached zero.
-         *
-         * At this point all target-core lun->lun_ref references have
-         * been dropped via transport_lun_remove_cmd(), and it's safe
-         * to proceed with the remaining LUN shutdown.
-         */
+        percpu_ref_kill(&lun->lun_ref);
         wait_for_completion(&lun->lun_shutdown_comp);
 }