linux-kernel - Re: [PATCH] scsi: Add intermediate STARGET_REMOVE state to scsi_target

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Date:	Thu, 24 Mar 2016 11:42:44 -0400
From:	"Ewan D. Milne" <emilne@...hat.com>
To:	Johannes Thumshirn <jthumshirn@...e.de>
Cc:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	"James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Hannes Reinecke <hare@...e.de>, stable@...r.kernel.org
Subject: Re: [PATCH] scsi: Add intermediate STARGET_REMOVE state to
 scsi_target_state

On Thu, 2016-03-24 at 10:56 +0100, Johannes Thumshirn wrote:
> The target state machine only knows 'STARGET_DEL', which is set once
> scsi_target_destroy() is called.
> However, by that time the structure is still part of the __stargets
> list of the SCSI host, so any concurrent invocation will see this as
> a valid target, causing an access to freed memory.
> 
> This patch adds an intermediate state 'STARGET_REMOVE', which is set
> as soon as the target is scheduled to be removed.
> With this any concurrent invocation will be able to skip these
> targets and avoid the above scenario.
> 
> Signed-off-by: Johannes Thumshirn <jthumshirn@...e.de>
> Fixes: 90a88d6ef 'scsi: fix soft lockup in scsi_remove_target() on module removal'
> Cc: stable@...r.kernel.org
> Reviewed-by: Hannes Reinecke <hare@...e.com>
> ---
>  drivers/scsi/scsi_scan.c   | 1 +
>  drivers/scsi/scsi_sysfs.c  | 2 ++
>  include/scsi/scsi_device.h | 1 +
>  3 files changed, 4 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
> index 6a82066..37459dfa 100644
> --- a/drivers/scsi/scsi_scan.c
> +++ b/drivers/scsi/scsi_scan.c
> @@ -315,6 +315,7 @@ static void scsi_target_destroy(struct scsi_target *starget)
>  	struct Scsi_Host *shost = dev_to_shost(dev->parent);
>  	unsigned long flags;
>  
> +	BUG_ON(starget->state != STARGET_REMOVE);
>  	starget->state = STARGET_DEL;
>  	transport_destroy_device(dev);
>  	spin_lock_irqsave(shost->host_lock, flags);
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index 00bc721..0df82e8 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -1279,11 +1279,13 @@ restart:
>  	spin_lock_irqsave(shost->host_lock, flags);
>  	list_for_each_entry(starget, &shost->__targets, siblings) {
>  		if (starget->state == STARGET_DEL ||
> +		    starget->state == STARGET_REMOVE ||
>  		    starget == last_target)
>  			continue;
>  		if (starget->dev.parent == dev || &starget->dev == dev) {
>  			kref_get(&starget->reap_ref);
>  			last_target = starget;
> +			starget->state = STARGET_REMOVE;
>  			spin_unlock_irqrestore(shost->host_lock, flags);
>  			__scsi_remove_target(starget);
>  			scsi_target_reap(starget);
> diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
> index f63a167..2bffaa6 100644
> --- a/include/scsi/scsi_device.h
> +++ b/include/scsi/scsi_device.h
> @@ -240,6 +240,7 @@ scmd_printk(const char *, const struct scsi_cmnd *, const char *, ...);
>  enum scsi_target_state {
>  	STARGET_CREATED = 1,
>  	STARGET_RUNNING,
> +	STARGET_REMOVE,
>  	STARGET_DEL,
>  };
>  

This looks fine.  Do we still need 90a88d6ef (scsi: fix soft lockup in
scsi_remove_target() on module removal) or can that be reverted now,
since the STARGET_REMOVE state will allow the iteration to continue?

Reviewed-by: Ewan D. Milne <emilne@...hat.com>