Re: [PATCH] sg: remove unreachable code in SET_FORCE_LOW_DMA

[Hannes Reinecke <hare@suse.de>]

On 02/01/2017 02:00 PM, Christoph Hellwig wrote:
> On Wed, Feb 01, 2017 at 12:26:39PM +0100, Hannes Reinecke wrote:
>> The low_dma value is always '1' in that branch, so the remaining
>> 'if' statement can never be reached.
>>
>>
>> Signed-off-by: Hannes Reinecke <hare@suse.com>
>> ---
>>  drivers/scsi/sg.c | 9 ++-------
>>  1 file changed, 2 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
>> index dbe5b4b..652b934 100644
>> --- a/drivers/scsi/sg.c
>> +++ b/drivers/scsi/sg.c
>> @@ -890,14 +890,9 @@ static int max_sectors_bytes(struct request_queue *q)
>>  		result = get_user(val, ip);
>>  		if (result)
>>  			return result;
>> -		if (val) {
>> +		if (val)
>>  			sfp->low_dma = 1;
>> -			if ((0 == sfp->low_dma) && (0 == sg_res_in_use(sfp))) {
>> -				val = (int) sfp->reserve.bufflen;
>> -				sg_remove_scat(sfp, &sfp->reserve);
>> -				sg_build_reserve(sfp, val);
>> -			}
>> -		} else {
>> +		else {
> 
> I think the proper fix is to check sfp->low_dma for 0 before updating
> it, at least that seems to be the intent here.
> 
May. Or may not.

But this code path has _never_ been taken for the last ten years; this
particular code predates the initial git check-in from Linus.
Where would be the point of enabling it now?
(Especially given all the issues we're having with the sg driver ...)

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
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