Kernel crash with target-pending/for-next

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

On Thu, 2017-06-01 at 18:17 +0000, Bart Van Assche wrote:
> Hello Nic,
> 
> This morning I started testing your for-next branch (commit b968ec8ff101
> with no changes). After a few seconds a kernel crash was triggered (see below).
> In the many tests I ran during the past two years of the ib_srpt driver I had
> not encountered any crash triggered by ib_srpt so this must be a recently
> introduced regression in the target core. This regression most likely has been
> introduced by one of these patches:
> 
> b968ec8ff101 target/configfs: Kill se_lun->lun_link_magic
> baacb554a73b target/configfs: Kill se_device->dev_link_magic
> ba438d7c8d39 target: Avoid target_shutdown_sessions loop during queue_depth change

Alas, the local list and unprotected list_del_init() ba438d7c8d won't
work for all fabric cases.

Here's the updated version to restore original behavior for se_node_acl
delete, but still avoid the endless loop with the iscsi-target specific
case where se_node_acl->queue_depth changes.

Care to verify on ib_srpt, or just a report and never confirm..?

From 9fdc33be4ef60ba87c8bf8a4dab6e756ec3b06e6 Mon Sep 17 00:00:00 2001
From: Nicholas Bellinger <nab@linux-iscsi.org>
Date: Thu, 1 Jun 2017 08:57:15 +0200
Subject: [PATCH-v2] target: Avoid target_shutdown_sessions loop during
 queue_depth change

When target_shutdown_sessions() is invoked to shutdown all active
sessions associated with a se_node_acl when se_node_acl->queue_depth
is changed via core_tpg_set_initiator_node_queue_depth(), it's
possible that new connections reconnect immediately after explicit
shutdown occurs via target_shutdown_sessions().

Which means it's possible for the newly reconnected session with
the proper queue_depth can be shutdown multiple times when
target_shutdown_sessions() loops to drain all active sessions
for all cases.

This was regression was introduced by:

  commit bc6e6bb470eda42f44bcac96c261cff1216577b3
  Author: Christoph Hellwig <hch@lst.de>
  Date:   Mon May 2 15:45:19 2016 +0200

      target: consolidate and fix session shutdown

To avoid this case, instead change target_shutdown_sessions() to
pass 'do_restart' and avoid the looping drain of sessions when
invoked via core_tpg_set_initiator_node_queue_depth(), but still
loop during normal se_node_acl delete until all associated
sessions have been shutdown.

(v2 - go back to the original version instead of a local list,
 in order to protect list_del_init(&sess->sess_acl_list) from
 transport_deregister_session_configfs.
 Also use safe list walking in target_shutdown_sessions - nab)

Cc: Christoph Hellwig <hch@lst.de>
Cc: Mike Christie <mchristi@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
---
 drivers/target/target_core_tpg.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

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Kernel crash with target-pending/for-next

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