Re: [bug] ata subsystem related crash with latest -git

Jens Axboe
2007-10-18T09:42:17Z

On Thu, Oct 18 2007, Jeff Garzik wrote:
> Jens Axboe wrote:
>> The sata_mv construct looks a bit odd. Does this work? That last
>
> The sata_mv construct worked just fine before sg chaining :)

Yes I know, but I'm trying to works towards getting rid of sg_last() and
ata_sg_is_last() anyway :-)

>> end_mv_sg test should always be true, just being paranoid...
>> diff --git a/drivers/ata/sata_mv.c b/drivers/ata/sata_mv.c
>> index 4df8311..5397eea 100644
>> --- a/drivers/ata/sata_mv.c
>> +++ b/drivers/ata/sata_mv.c
>> @@ -1138,8 +1138,9 @@ static void mv_fill_sg(struct ata_queued_cmd *qc)
>> {
>> struct mv_port_priv *pp = qc->ap->private_data;
>> struct scatterlist *sg;
>> - struct mv_sg *mv_sg;
>> + struct mv_sg *mv_sg, *end_mv_sg;
>> + end_mv_sg = NULL;
>> mv_sg = pp->sg_tbl;
>> ata_for_each_sg(sg, qc) {
>> dma_addr_t addr = sg_dma_address(sg);
>> @@ -1158,14 +1159,12 @@ static void mv_fill_sg(struct ata_queued_cmd *qc)
>> sg_len -= len;
>> addr += len;
>> -
>> - if (!sg_len && ata_sg_is_last(sg, qc))
>> - mv_sg->flags_size |= cpu_to_le32(EPRD_FLAG_END_OF_TBL);
>> -
>> + end_mv_sg = mv_sg;
>> mv_sg++;
>> }
>> -
>> }
>> + if (end_mv_sg)
>> + end_mv_sg->flags_size |= cpu_to_le32(EPRD_FLAG_END_OF_TBL);
>> }
>>
>
> I'm testing a similar patch based on ata_fill_sg()'s method, which
> basically does something similar to what you've done here (see attached).
> I had noticed that ata_fill_sg() did not call ata_sg_is_last().
>
> If this fixes the problem, I think the best solution would be to delete
> ata_sg_is_last(). In the few users that exist, we should be able to
> eliminate the test programmatically as you and ata_fill_sg() have done --
> thereby eliminating a branch per loop in a hotpath.
>
> Off to test the attached... if that doesn't work I'll try your version,
> though there shouldn't be much difference.

That should work as well. WRT ata_sg_is_last(), if we go ahead with my
recent sg chaining updates, we can keep the test as it would be a single
conditional and not require any looping.

Let me know when you have tested this!

--
Jens Axboe