Re: [PATCH 2/2] Restart list search after unlock in scsi_remove_target

[Bart Van Assche <bart.vanassche@sandisk.com>]

On 10/30/2015 03:09 PM, Bart Van Assche 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.
>
> This is a slightly modified version of a patch from Christoph Hellwig
> (see also https://www.spinics.net/lists/linux-scsi/msg89416.html).
>
> Reported-by: Johannes Thumshirn <jthumshirn@suse.de>
> Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
> Cc: Johannes Thumshirn <jthumshirn@suse.de>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: stable <stable@vger.kernel.org>
> ---
>   drivers/scsi/scsi_sysfs.c | 16 ++++------------
>   1 file changed, 4 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index b9fb61a..5a183d1 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -1158,32 +1158,24 @@ 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->reaped)
>   			continue;
>   		if (starget->dev.parent == dev || &starget->dev == dev) {
> -			/* assuming new targets arrive at the end */
>   			kref_get(&starget->reap_ref);
>   			starget->reaped = true;
>   			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);

(replying to my own e-mail)

Hello Christoph,

Is it OK for you if I mention you as author of this e-mail ?

Thanks,

Bart.