From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 2/4] sg: protect access to to 'reserved' page array
Date: Fri, 3 Feb 2017 11:24:32 +0100
Message-ID: <20170203102432.GB29163@lst.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, stable@vger.kernel.org, Hannes Reinecke <hare@suse.com>
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On Fri, Feb 03, 2017 at 09:54:49AM +0100, Hannes Reinecke wrote:
> The 'reserved' page array is used as a short-cut for mapping
> data, saving us to allocate pages per request.
> However, the 'reserved' array is only capable of holding one
> request, so we need to protect it against concurrent accesses.

Can you please explain how you protect the access here a bit more,
as mentioned before the set_bit for exclusion trick is always
suspicious, so the changelog needs to have a justification for it.