From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCHv3 3/6] sg: protect accesses to 'reserved' page array
Date: Fri, 3 Feb 2017 17:19:10 +0100
Message-ID: <20170203161910.GA4339@lst.de>
References: <1486127531-13716-1-git-send-email-hare@suse.de> <1486127531-13716-4-git-send-email-hare@suse.de> <20170203133140.GC646@lst.de> <b75d63b6-ae38-6c69-ec16-430e2bd351f7@suse.de>
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To: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@lst.de>, "Martin K. Petersen" <martin.petersen@oracle.com>, James Bottomley <james.bottomley@hansenpartnership.com>, Johannes Thumshirn <jth@kernel.org>, Doug Gilberg <dgilbert@interlog.com>, linux-scsi@vger.kernel.org, Hannes Reinecke <hare@suse.com>

On Fri, Feb 03, 2017 at 02:38:35PM +0100, Hannes Reinecke wrote:
> On 02/03/2017 02:31 PM, Christoph Hellwig wrote:
> >> -		if (sg_res_in_use(sfp)) {
> >> +		mutex_lock(&sfp->f_mutex);
> >> +		if (sfp->res_in_use) {
> >> +			mutex_unlock(&sfp->f_mutex);
> >>  			sg_remove_request(sfp, srp);
> >>  			return -EBUSY;	/* reserve buffer already being used */
> >>  		}
> >> +		mutex_unlock(&sfp->f_mutex);
> > 
> > Holding a mutex over a the check of a single scalar doesn't make sense.
> > 
> It's adds a synchronisation point, doesn't it?

It does, but it doesn't actually protect anything..