linux-kernel - Re: [PATCH RESEND] xen/blkfront: improve protection against issuing unsupported REQ

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Message-ID: <87wq68k6jd.fsf@vitty.brq.redhat.com>
Date:	Wed, 03 Dec 2014 18:05:42 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Laszlo Ersek <lersek@...hat.com>,
	Andrew Jones <drjones@...hat.com>,
	Jeff Moyer <jmoyer@...hat.com>, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH RESEND] xen/blkfront: improve protection against issuing unsupported REQ_FUA

Boris Ostrovsky <boris.ostrovsky@...cle.com> writes:

> On 12/01/2014 08:01 AM, Vitaly Kuznetsov wrote:
>> Guard against issuing unsupported REQ_FUA and REQ_FLUSH was introduced
>> in d11e61583 and was factored out into blkif_request_flush_valid() in
>> 0f1ca65ee. However:
>> 1) This check in incomplete. In case we negotiated to feature_flush = REQ_FLUSH
>>     and flush_op = BLKIF_OP_FLUSH_DISKCACHE (so FUA is unsupported) FUA request
>>     will still pass the check.
>> 2) blkif_request_flush_valid() is misnamed. It is bool but returns true when
>>     the request is invalid.
>> 3) When blkif_request_flush_valid() fails -EIO is being returned. It seems that
>>     -EOPNOTSUPP is more appropriate here.
>> Fix all of the above issues.
>>
>> This patch is based on the original patch by Laszlo Ersek and a comment by
>> Jeff Moyer.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> Reviewed-by: Laszlo Ersek <lersek@...hat.com>
>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>
> (although, as I mentioned last time, a companion patch to remove
> flush_op would be a good thing to have)
>

Thanks, it is on my todo list but I'm trying to separate this
(potential) bugfix from straight cleanup.

> -boris
>
>> ---
>>   drivers/block/xen-blkfront.c | 14 ++++++++------
>>   1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>> index 5ac312f..2e6c103 100644
>> --- a/drivers/block/xen-blkfront.c
>> +++ b/drivers/block/xen-blkfront.c
>> @@ -582,12 +582,14 @@ static inline void flush_requests(struct blkfront_info *info)
>>   		notify_remote_via_irq(info->irq);
>>   }
>>   -static inline bool blkif_request_flush_valid(struct request *req,
>> -					     struct blkfront_info *info)
>> +static inline bool blkif_request_flush_invalid(struct request *req,
>> +					       struct blkfront_info *info)
>>   {
>>   	return ((req->cmd_type != REQ_TYPE_FS) ||
>> -		((req->cmd_flags & (REQ_FLUSH | REQ_FUA)) &&
>> -		!info->flush_op));
>> +		((req->cmd_flags & REQ_FLUSH) &&
>> +		 !(info->feature_flush & REQ_FLUSH)) ||
>> +		((req->cmd_flags & REQ_FUA) &&
>> +		 !(info->feature_flush & REQ_FUA)));
>>   }
>>     /*
>> @@ -612,8 +614,8 @@ static void do_blkif_request(struct request_queue *rq)
>>     		blk_start_request(req);
>>   -		if (blkif_request_flush_valid(req, info)) {
>> -			__blk_end_request_all(req, -EIO);
>> +		if (blkif_request_flush_invalid(req, info)) {
>> +			__blk_end_request_all(req, -EOPNOTSUPP);
>>   			continue;
>>   		}
>>   

-- 
  Vitaly
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