Re: [PATCH] scsi: restart list search after unlock in scsi_remove_target

[Johannes Thumshirn <jthumshirn@suse.de>]

On Mon, 2015-10-19 at 16:35 +0200, Christoph Hellwig wrote:
> When dropping a lock while iterating a list we must restart the
> search
> as other threads could have manipulated the list under us.  Without
> this
> we can get stuck in an endless loop.
> 
> Reported-by: Johannes Thumshirn <jthumshirn@suse.de>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index b333389f..d3b34d8 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -1158,31 +1158,23 @@ static void __scsi_remove_target(struct
> scsi_target *starget)
>  void scsi_remove_target(struct device *dev)
>  {
>  	struct Scsi_Host *shost = dev_to_shost(dev->parent);
> -	struct scsi_target *starget, *last = NULL;
> +	struct scsi_target *starget;
>  	unsigned long flags;
>  
> -	/* remove targets being careful to lookup next entry before
> -	 * deleting the last
> -	 */
> +restart:
>  	spin_lock_irqsave(shost->host_lock, flags);
>  	list_for_each_entry(starget, &shost->__targets, siblings) {
>  		if (starget->state == STARGET_DEL)
>  			continue;
>  		if (starget->dev.parent == dev || &starget->dev ==
> dev) {
> -			/* assuming new targets arrive at the end */
>  			kref_get(&starget->reap_ref);
>  			spin_unlock_irqrestore(shost->host_lock,
> flags);
> -			if (last)
> -				scsi_target_reap(last);
> -			last = starget;
>  			__scsi_remove_target(starget);
> -			spin_lock_irqsave(shost->host_lock, flags);
> +			scsi_target_reap(starget);
> +			goto restart;
>  		}
>  	}
>  	spin_unlock_irqrestore(shost->host_lock, flags);
> -
> -	if (last)
> -		scsi_target_reap(last);
>  }
>  EXPORT_SYMBOL(scsi_remove_target);

Hi Christoph,

I haven't heard anything from the original reporter of the lockup but
my test's went all O.K., so 

Tested-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>

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