linux-kernel - [PATCH 4.4 064/115] target: Use system workqueue for ALUA transitions

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Message-Id: <20171218152856.778650728@linuxfoundation.org>
Date:   Mon, 18 Dec 2017 16:48:53 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mike Christie <mchristi@...hat.com>,
        Nicholas Bellinger <nab@...ux-iscsi.org>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.4 064/115] target: Use system workqueue for ALUA transitions

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mike Christie <mchristi@...hat.com>

[ 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.

Signed-off-by: Mike Christie <mchristi@...hat.com>
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/target/target_core_alua.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

--- a/drivers/target/target_core_alua.c
+++ b/drivers/target/target_core_alua.c
@@ -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;
 	}