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 14:31:40 +0100
Message-ID: <20170203133140.GC646@lst.de>
References: <1486127531-13716-1-git-send-email-hare@suse.de> <1486127531-13716-4-git-send-email-hare@suse.de>
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To: Hannes Reinecke <hare@suse.de>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>, Christoph Hellwig <hch@lst.de>, 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>

> -		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.