From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [PATCH 2/2] Restart list search after unlock in scsi_remove_target Date: Wed, 04 Nov 2015 14:44:32 -0800 Message-ID: <1446677072.2216.30.camel@HansenPartnership.com> References: <5633E9F2.5080209@sandisk.com> <5633EA98.8050604@sandisk.com> <563A883C.9060501@sandisk.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from bedivere.hansenpartnership.com ([66.63.167.143]:54044 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031007AbbKDWoe (ORCPT ); Wed, 4 Nov 2015 17:44:34 -0500 In-Reply-To: <563A883C.9060501@sandisk.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Bart Van Assche Cc: Christoph Hellwig , Johannes Thumshirn , Dan Williams , "linux-scsi@vger.kernel.org" On Wed, 2015-11-04 at 14:35 -0800, Bart Van Assche wrote: > 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 > > Signed-off-by: Bart Van Assche > > Cc: Johannes Thumshirn > > Cc: Christoph Hellwig > > Cc: Dan Williams > > Cc: stable > > --- > > 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 ? Could you just both co-operate, especially since there's not much difference between the patches. The fundamental problem with this is how have the conditions that caused us to move away from list restart: commit bc3f02a795d3b4faa99d37390174be2a75d091bd Author: Dan Williams Date: Tue Aug 28 22:12:10 2012 -0700 [SCSI] scsi_remove_target: fix softlockup regression on hot remove Which was triggered by this bug report http://thread.gmane.org/gmane.linux.kernel/1348679 been mitigated? James