linux-kernel - [PATCH 3.16 093/346] target: Fix missing complete during ABORT_TASK + CMD_T_FABRIC

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Date:   Mon, 14 Nov 2016 00:14:20 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Mike Christie" <mchristi@...hat.com>,
        "Christoph Hellwig" <hch@....de>, "Hannes Reinecke" <hare@...e.de>,
        "Himanshu Madhani" <himanshu.madhani@...gic.com>,
        "Quinn Tran" <quinn.tran@...gic.com>,
        "Nicholas Bellinger" <nab@...ux-iscsi.org>
Subject: [PATCH 3.16 093/346] target: Fix missing complete during
 ABORT_TASK + CMD_T_FABRIC_STOP

3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Nicholas Bellinger <nab@...ux-iscsi.org>

commit 5e2c956b8aa24d4f33ff7afef92d409eed164746 upstream.

During transport_generic_free_cmd() with a concurrent TMR
ABORT_TASK and shutdown CMD_T_FABRIC_STOP bit set, the
caller will be blocked on se_cmd->cmd_wait_stop completion
until the final kref_put() -> target_release_cmd_kref()
has been invoked to call complete().

However, when ABORT_TASK is completed with FUNCTION_COMPLETE
in core_tmr_abort_task(), the aborted se_cmd will have already
been removed from se_sess->sess_cmd_list via list_del_init().

This results in target_release_cmd_kref() hitting the
legacy list_empty() == true check, invoking ->release_cmd()
but skipping complete() to wakeup se_cmd->cmd_wait_stop
blocked earlier in transport_generic_free_cmd() code.

To address this bug, it's safe to go ahead and drop the
original list_empty() check so that fabric_stop invokes
the complete() as expected, since list_del_init() can
safely be used on a empty list.

Cc: Mike Christie <mchristi@...hat.com>
Cc: Quinn Tran <quinn.tran@...gic.com>
Cc: Himanshu Madhani <himanshu.madhani@...gic.com>
Cc: Christoph Hellwig <hch@....de>
Cc: Hannes Reinecke <hare@...e.de>
Tested-by: Nicholas Bellinger <nab@...ux-iscsi.org>
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/target/target_core_transport.c | 6 ------
 1 file changed, 6 deletions(-)

--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -2455,12 +2455,6 @@ static void target_release_cmd_kref(stru
 	struct se_session *se_sess = se_cmd->se_sess;
 	bool fabric_stop;

-	if (list_empty(&se_cmd->se_cmd_list)) {
-		spin_unlock(&se_sess->sess_cmd_lock);
-		target_free_cmd_mem(se_cmd);
-		se_cmd->se_tfo->release_cmd(se_cmd);
-		return;
-	}

 	spin_lock(&se_cmd->t_state_lock);
 	fabric_stop = (se_cmd->transport_state & CMD_T_FABRIC_STOP);