Re: [PATCH] scsi: Add intermediate STARGET_REMOVE state to scsi_target_state

[Johannes Thumshirn]

On Donnerstag, 24. März 2016 11:42:44 CEST Ewan D. Milne wrote:
> 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@xxxxxxx>
> > Fixes: 90a88d6ef 'scsi: fix soft lockup in scsi_remove_target() on module
> > removal' Cc: stable@xxxxxxxxxxxxxxx
> > Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>
> > ---
> > 
> >  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@xxxxxxxxxx>

We've tested it on-top of 90a88d6ef, so I'm not quite sure.

Anyways, I've seen a mail from the 0-day bot regarding this patch, so I'll 
have to check that one first.

-- 
Johannes Thumshirn                                          Storage
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