Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 18 Feb 2020 09:23:47 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     James Bottomley <jejb@linux.ibm.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Merlijn Wajer <merlijn@archive.org>, merlijn@wizzup.org,
        linux-scsi@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Arnd Bergmann <arnd@arndb.de>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] scsi: sr: get rid of sr global mutex
Message-ID: <20200218172347.GA3020@infradead.org>
References: <20200218143918.30267-1-merlijn@archive.org>
 <20200218171259.GA6724@infradead.org>
 <1582046428.16681.7.camel@linux.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1582046428.16681.7.camel@linux.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Feb 18, 2020 at 09:20:28AM -0800, James Bottomley wrote:
> > > Replace the global mutex with per-sr-device mutex.
> > 
> > Do we actually need the lock at all?  What is protected by it?
> 
> We do at least for cdrom_open.  It modifies the cdi structure with no
> other protection and concurrent modification would at least screw up
> the use counter which is not atomic.  Same reasoning for cdrom_release.

Wouldn't the right fix to add locking to cdrom_open/release instead of
having an undocumented requirement for the callers?