Commit 3bd6f43f authored by Bart Van Assche's avatar Bart Van Assche Committed by Martin K. Petersen
Browse files

scsi: core: Ensure that the SCSI error handler gets woken up 



If scsi_eh_scmd_add() is called concurrently with
scsi_host_queue_ready() while shost->host_blocked > 0 then it can
happen that neither function wakes up the SCSI error handler. Fix
this by making every function that decreases the host_busy counter
wake up the error handler if necessary and by protecting the
host_failed checks with the SCSI host lock.

Reported-by: default avatarPavel Tikhomirov <ptikhomirov@virtuozzo.com>
References: https://marc.info/?l=linux-kernel&m=150461610630736


Fixes: commit 74665016 ("scsi: convert host_busy to atomic_t")
Signed-off-by: default avatarBart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: default avatarPavel Tikhomirov <ptikhomirov@virtuozzo.com>
Tested-by: default avatarStuart Hayes <stuart.w.hayes@gmail.com>
Cc: Konstantin Khorenko <khorenko@virtuozzo.com>
Cc: Stuart Hayes <stuart.w.hayes@gmail.com>
Cc: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
parent 156baec3

drivers/scsi/hosts.c

+6 −0
Original line number Diff line number Diff line
@@ -318,6 +318,9 @@ static void scsi_host_dev_release(struct device *dev) 


	scsi_proc_hostdir_rm(shost->hostt);



	/* Wait for functions invoked through call_rcu(&shost->rcu, ...) */

	rcu_barrier();



	if (shost->tmf_work_q)

		destroy_workqueue(shost->tmf_work_q);

	if (shost->ehandler)
@@ -325,6 +328,8 @@ static void scsi_host_dev_release(struct device *dev) 
	if (shost->work_q)

		destroy_workqueue(shost->work_q);



	destroy_rcu_head(&shost->rcu);



	if (shost->shost_state == SHOST_CREATED) {

		/*

		 * Free the shost_dev device name here if scsi_host_alloc()
@@ -399,6 +404,7 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize) 
	INIT_LIST_HEAD(&shost->starved_list);

	init_waitqueue_head(&shost->host_wait);

	mutex_init(&shost->scan_mutex);

	init_rcu_head(&shost->rcu);



	index = ida_simple_get(&host_index_ida, 0, 0, GFP_KERNEL);

	if (index < 0)

drivers/scsi/scsi_error.c

+16 −2
Original line number Diff line number Diff line
@@ -220,6 +220,17 @@ static void scsi_eh_reset(struct scsi_cmnd *scmd) 
	}

}



static void scsi_eh_inc_host_failed(struct rcu_head *head)

{

	struct Scsi_Host *shost = container_of(head, typeof(*shost), rcu);

	unsigned long flags;



	spin_lock_irqsave(shost->host_lock, flags);

	shost->host_failed++;

	scsi_eh_wakeup(shost);

	spin_unlock_irqrestore(shost->host_lock, flags);

}



/**

 * scsi_eh_scmd_add - add scsi cmd to error handling.

 * @scmd:	scmd to run eh on.
@@ -242,9 +253,12 @@ void scsi_eh_scmd_add(struct scsi_cmnd *scmd) 


	scsi_eh_reset(scmd);

	list_add_tail(&scmd->eh_entry, &shost->eh_cmd_q);

	shost->host_failed++;

	scsi_eh_wakeup(shost);

	spin_unlock_irqrestore(shost->host_lock, flags);

	/*

	 * Ensure that all tasks observe the host state change before the

	 * host_failed change.

	 */

	call_rcu(&shost->rcu, scsi_eh_inc_host_failed);

}



/**

drivers/scsi/scsi_lib.c

+28 −11
Original line number Diff line number Diff line
@@ -318,22 +318,39 @@ static void scsi_init_cmd_errh(struct scsi_cmnd *cmd) 
		cmd->cmd_len = scsi_command_size(cmd->cmnd);

}



void scsi_device_unbusy(struct scsi_device *sdev)

/*

 * Decrement the host_busy counter and wake up the error handler if necessary.

 * Avoid as follows that the error handler is not woken up if shost->host_busy

 * == shost->host_failed: use call_rcu() in scsi_eh_scmd_add() in combination

 * with an RCU read lock in this function to ensure that this function in its

 * entirety either finishes before scsi_eh_scmd_add() increases the

 * host_failed counter or that it notices the shost state change made by

 * scsi_eh_scmd_add().

 */

static void scsi_dec_host_busy(struct Scsi_Host *shost)

{

	struct Scsi_Host *shost = sdev->host;

	struct scsi_target *starget = scsi_target(sdev);

	unsigned long flags;



	rcu_read_lock();

	atomic_dec(&shost->host_busy);

	if (starget->can_queue > 0)

		atomic_dec(&starget->target_busy);



	if (unlikely(scsi_host_in_recovery(shost) &&

		     (shost->host_failed || shost->host_eh_scheduled))) {

	if (unlikely(scsi_host_in_recovery(shost))) {

		spin_lock_irqsave(shost->host_lock, flags);

		if (shost->host_failed || shost->host_eh_scheduled)

			scsi_eh_wakeup(shost);

		spin_unlock_irqrestore(shost->host_lock, flags);

	}

	rcu_read_unlock();

}



void scsi_device_unbusy(struct scsi_device *sdev)

{

	struct Scsi_Host *shost = sdev->host;

	struct scsi_target *starget = scsi_target(sdev);



	scsi_dec_host_busy(shost);



	if (starget->can_queue > 0)

		atomic_dec(&starget->target_busy);



	atomic_dec(&sdev->device_busy);

}
@@ -1532,7 +1549,7 @@ starved: 
		list_add_tail(&sdev->starved_entry, &shost->starved_list);

	spin_unlock_irq(shost->host_lock);

out_dec:

	atomic_dec(&shost->host_busy);

	scsi_dec_host_busy(shost);

	return 0;

}
@@ -2018,7 +2035,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx, 
	return BLK_STS_OK;



out_dec_host_busy:

       atomic_dec(&shost->host_busy);

	scsi_dec_host_busy(shost);

out_dec_target_busy:

	if (scsi_target(sdev)->can_queue > 0)

		atomic_dec(&scsi_target(sdev)->target_busy);

include/scsi/scsi_host.h

+2 −0
Original line number Diff line number Diff line
@@ -571,6 +571,8 @@ struct Scsi_Host { 
		struct blk_mq_tag_set	tag_set;

	};



	struct rcu_head rcu;



	atomic_t host_busy;		   /* commands actually active on low-level */

	atomic_t host_blocked;

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