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

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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@xxxxxxx>
Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
---
  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.


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