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>

diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
index cffd743..1d51df2 100644 (file)
--- 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 16e7a65..e2ace10 100644 (file)
--- 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 4d1651e..0c8eca6 100644 (file)
--- 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);
 }
 

diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 53b90cc..bb965a3 100644 (file)
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -733,7 +733,6 @@ struct se_lun {
        struct scsi_port_stats  lun_stats;
        struct config_group     lun_group;
        struct se_port_stat_grps port_stat_grps;
-       struct completion       lun_ref_comp;
        struct completion       lun_shutdown_comp;
        struct percpu_ref       lun_ref;
        struct list_head        lun_dev_link;