linux-kernel - Re: [PATCH 2/2] target: Fix target_wait_for_sess

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Date:   Wed, 10 Oct 2018 04:01:17 +0000
From:   "Ly, Bryant" <bly@...alogicsoftware.com>
To:     "Nicholas A. Bellinger" <nab@...ux-iscsi.org>
CC:     target-devel <target-devel@...r.kernel.org>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Mike Christie <mchristi@...hat.com>,
        Hannes Reinecke <hare@...e.com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        "Bryant G. Ly" <bryantly@...ux.vnet.ibm.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Bart Van Assche <bvanassche@....org>
Subject: Re: [PATCH 2/2] target: Fix target_wait_for_sess_cmds breakage with
 active signals



> On Oct 9, 2018, at 10:23 PM, Nicholas A. Bellinger <nab@...ux-iscsi.org> wrote:
> 
> From: Nicholas Bellinger <nab@...ux-iscsi.org>
> 
> With the addition of commit 00d909a107 in v4.19-rc, it incorrectly assumes no
> signals will be pending for task_struct executing the normal session shutdown
> and I/O quiesce code-path.
> 
> For example, iscsi-target and iser-target issue SIGINT to all kthreads as
> part of session shutdown.  This has been the behaviour since day one.
> 
> As-is when signals are pending with se_cmds active in se_sess->sess_cmd_list,
> wait_event_interruptible_lock_irq_timeout() returns a negative number and
> immediately kills the machine because of the do while (ret <= 0) loop that
> was added in commit 00d909a107 to spin while backend I/O is taking any
> amount of extended time (say 30 seconds) to complete.
> 
> Here's what it looks like in action with debug plus delayed backend I/O
> completion:
> 
> [ 4951.909951] se_sess: 000000003e7e08fa before target_wait_for_sess_cmds
> [ 4951.914600] target_wait_for_sess_cmds: signal_pending: 1
> [ 4951.918015] wait_event_interruptible_lock_irq_timeout ret: -512 signal_pending: 1 loop count: 0
> [ 4951.921639] wait_event_interruptible_lock_irq_timeout ret: -512 signal_pending: 1 loop count: 1
> [ 4951.921944] wait_event_interruptible_lock_irq_timeout ret: -512 signal_pending: 1 loop count: 2
> [ 4951.921944] wait_event_interruptible_lock_irq_timeout ret: -512 signal_pending: 1 loop count: 3
> [ 4951.921944] wait_event_interruptible_lock_irq_timeout ret: -512 signal_pending: 1 loop count: 4
> [ 4951.921944] wait_event_interruptible_lock_irq_timeout ret: -512 signal_pending: 1 loop count: 5
> [ 4951.921944] wait_event_interruptible_lock_irq_timeout ret: -512 signal_pending: 1 loop count: 6
> [ 4951.921944] wait_event_interruptible_lock_irq_timeout ret: -512 signal_pending: 1 loop count: 7
> [ 4951.921944] wait_event_interruptible_lock_irq_timeout ret: -512 signal_pending: 1 loop count: 8
> [ 4951.921944] wait_event_interruptible_lock_irq_timeout ret: -512 signal_pending: 1 loop count: 9
> 
> ... followed by the usual RCU CPU stalls and deadlock.
> 
> There was never a case pre commit 00d909a107 where wait_for_complete(&se_cmd->cmd_wait_comp)
> was able to be interruptted, so to address this for v4.19+ moving forward go ahead and
> use wait_event_lock_irq_timeout() instead so new code works with all fabric drivers.
> 
> Also for commit 00d909a107, fix a minor regression in target_release_cmd_kref()
> to only wake_up the new se_sess->cmd_list_wq only when shutdown has actually
> been triggered via se_sess->sess_tearing_down.
> 
> Fixes: 00d909a107 ("scsi: target: Make the session shutdown code also wait for commands that are being aborted")
> Cc: Bart Van Assche <bvanassche@....org>
> Cc: Mike Christie <mchristi@...hat.com>
> Cc: Hannes Reinecke <hare@...e.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Sagi Grimberg <sagi@...mberg.me>
> Cc: Bryant G. Ly <bryantly@...ux.vnet.ibm.com>
> Tested-by: Nicholas Bellinger <nab@...ux-iscsi.org>
> Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
> ---
> drivers/target/target_core_transport.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 

Reviewed-by: Bryant G. Ly <bly@...alogicsoftware.com>

-Bryant