Patch "target: Use system workqueue for ALUA transitions" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

target: Use system workqueue for ALUA transitions

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
target-use-system-workqueue-for-alua-transitions.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Mike Christie <[email protected]>
Date: Wed, 1 Mar 2017 23:13:26 -0600
Subject: target: Use system workqueue for ALUA transitions

From: Mike Christie <[email protected]>

[ Upstream commit 207ee84133c00a8a2a5bdec94df4a5b37d78881c ]

If tcmu-runner is processing a STPG and needs to change the kernel's ALUA state then we cannot use the same work queue for task management requests and ALUA transitions, because we could deadlock. The problem occurs when a STPG times out before tcmu-runner is able to call into target_tg_pt_gp_alua_access_state_store-> core_alua_do_port_transition -> core_alua_do_transition_tg_pt -> queue_work. In this case, the tmr is on the work queue waiting for the STPG to complete, but the STPG transition is now queued behind the waiting tmr.

Note:
This bug will also be fixed by this patch:
http://www.spinics.net/lists/target-devel/msg14560.html
which switches the tmr code to use the system workqueues.

For both, I am not sure if we need a dedicated workqueue since it is not a performance path and I do not think we need WQ_MEM_RECLAIM to make forward progress to free up memory like the block layer does.

---
 drivers/target/target_core_alua.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

@@ -1118,13 +1118,11 @@ static int core_alua_do_transition_tg_pt
 		unsigned long transition_tmo;
 
 		transition_tmo = tg_pt_gp->tg_pt_gp_implicit_trans_secs * HZ;
-		queue_delayed_work(tg_pt_gp->tg_pt_gp_dev->tmr_wq,
-				   &tg_pt_gp->tg_pt_gp_transition_work,
-				   transition_tmo);
+		schedule_delayed_work(&tg_pt_gp->tg_pt_gp_transition_work,
+				      transition_tmo);
 	} else {
 		tg_pt_gp->tg_pt_gp_transition_complete = &wait;
-		queue_delayed_work(tg_pt_gp->tg_pt_gp_dev->tmr_wq,
-				   &tg_pt_gp->tg_pt_gp_transition_work, 0);
+		schedule_delayed_work(&tg_pt_gp->tg_pt_gp_transition_work, 0);
 		wait_for_completion(&wait);
 		tg_pt_gp->tg_pt_gp_transition_complete = NULL;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/target-use-system-workqueue-for-alua-transitions.patch queue-4.4/target-iscsi-fix-a-race-condition-in-iscsit_add_reject_from_cmd.patch queue-4.4/target-fix-alua-transition-timeout-handling.patch queue-4.4/target-fix-race-during-implicit-transition-work-flushes.patch