Re: [PATCH v2 3/4] scsi: Avoid that .queuecommand() gets called for a quiesced SCSI device

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From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "ming.lei@redhat.com" <ming.lei@redhat.com>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"jthumshirn@suse.de" <jthumshirn@suse.de>,
	"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
	"jgg@mellanox.com" <jgg@mellanox.com>, "hch@lst.de" <hch@lst.de>,
	"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
	"axboe@kernel.dk" <axboe@kernel.dk>,
	"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	"hare@suse.com" <hare@suse.com>,
	"dledford@redhat.com" <dledford@redhat.com>
Subject: Re: [PATCH v2 3/4] scsi: Avoid that .queuecommand() gets called for a quiesced SCSI device
Date: Fri, 12 Jan 2018 22:45:57 +0000	[thread overview]
Message-ID: <1515797155.2396.86.camel@wdc.com> (raw)
In-Reply-To: <20180111022341.GA7290@ming.t460p>

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WARNING: multiple messages have this Message-ID (diff)

From: Bart Van Assche <Bart.VanAssche-Sjgp3cTcYWE@public.gmane.org>
To: "ming.lei-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org"
	<ming.lei-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: "linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"jthumshirn-l3A5Bk7waGM@public.gmane.org"
	<jthumshirn-l3A5Bk7waGM@public.gmane.org>,
	"linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
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	"martin.petersen-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org"
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	"axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org"
	<axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>,
	"linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"hare-IBi9RG/b67k@public.gmane.org"
	<hare-IBi9RG/b67k@public.gmane.org>,
	"dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org"
	<dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH v2 3/4] scsi: Avoid that .queuecommand() gets called for a quiesced SCSI device
Date: Fri, 12 Jan 2018 22:45:57 +0000	[thread overview]
Message-ID: <1515797155.2396.86.camel@wdc.com> (raw)
In-Reply-To: <20180111022341.GA7290-1Cy0MwPVgsaKEAUSAb389g@public.gmane.org>

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On Thu, 2018-01-11 at 10:23 +0800, Ming Lei wrote:
> > not sufficient to prevent .queuecommand() calls from scsi_send_eh_cmnd().
> 
> Given it is error handling, do we need to prevent the .queuecommand() call
> in scsi_send_eh_cmnd()? Could you share us what the actual issue
> observed is from user view?

Please have a look at the kernel bug report in the description of patch 4/4 of
this series.

> > Hence surround the .queuecommand() call from the SCSI error handler with
> > blk_start_wait_if_quiesced() / blk_finish_wait_if_quiesced().
> > 
> > Note: converting the .queuecommand() call in scsi_send_eh_cmnd() into
> > code that calls blk_get_request(), e.g. scsi_execute_req(), is not an
> > option since scsi_send_eh_cmnd() can be called if all requests are
> > allocated and if no requests will make progress without aborting any
> > of these requests.
> 
> If we need to prevent the .queuecommand() in scsi_send_eh_cmnd(), what
> do you think of the approach by requeuing the EH command via
> scsi_mq_requeue_cmd()/scsi_requeue_cmd()? And the EH request will be
> dispatched finally when the queue becomes unquiesced or the STOPPED
> is cleared.

Calling scsi_mq_requeue_cmd() would trigger scsi_mq_uninit_cmd(),
blk_mq_put_driver_tag(), blk_mq_get_driver_tag() and scsi_mq_prep_fn().
That could cause scsi_eh_scmd_add() to be called multiple times for the
same SCSI command. However, that would break one of the assumptions
scsi_eh_scmd_add() is based on, namely that that function gets called
only once per SCSI command that is in progress.

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next prev parent reply	other threads:[~2018-01-12 22:45 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-10 18:18 [PATCH v2 0/4] Make SCSI transport recovery more robust Bart Van Assche
2018-01-10 18:18 ` Bart Van Assche
2018-01-10 18:18 ` [PATCH v2 1/4] blk-mq: Rename request_queue.mq_freeze_wq into mq_wq Bart Van Assche
2018-01-10 18:18   ` Bart Van Assche
2018-01-10 18:18 ` [PATCH v2 2/4] block: Introduce blk_start_wait_if_quiesced() and blk_finish_wait_if_quiesced() Bart Van Assche
2018-01-10 18:18   ` Bart Van Assche
2018-01-10 18:18 ` [PATCH v2 3/4] scsi: Avoid that .queuecommand() gets called for a quiesced SCSI device Bart Van Assche
2018-01-11  2:23   ` Ming Lei
2018-01-12 22:45     ` Bart Van Assche [this message]
2018-01-12 22:45       ` Bart Van Assche
2018-01-13 15:54       ` Ming Lei
2018-01-25 17:07         ` Bart Van Assche
2018-01-25 17:07           ` Bart Van Assche
2018-01-10 18:18 ` [PATCH v2 4/4] IB/srp: Fix a sleep-in-invalid-context bug Bart Van Assche
2018-01-10 18:18   ` Bart Van Assche
2018-01-13 15:42   ` Ming Lei
2018-01-13 15:42     ` Ming Lei

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