Hi,
On Tue, Jun 2, 2009 at 12:18 PM, Bartlomiej Zolnierkiewicz
<bzolnier@xxxxxxxxx> wrote:
..
>> --- a/drivers/ide/ide-tape.c
>> +++ b/drivers/ide/ide-tape.c
>> @@ -656,15 +656,24 @@ static ide_startstop_t idetape_do_request(ide_drive_t *drive,
>>
>> if ((drive->dev_flags & IDE_DFLAG_DSC_OVERLAP) == 0 &&
>> (rq->cmd[13] & REQ_IDETAPE_PC2) == 0)
>> - set_bit(IDE_AFLAG_IGNORE_DSC, &drive->atapi_flags);
>> + drive->atapi_flags |= IDE_AFLAG_IGNORE_DSC;
>>
>> if (drive->dev_flags & IDE_DFLAG_POST_RESET) {
>> - set_bit(IDE_AFLAG_IGNORE_DSC, &drive->atapi_flags);
>> + drive->atapi_flags |= IDE_AFLAG_IGNORE_DSC;
>> drive->dev_flags &= ~IDE_DFLAG_POST_RESET;
>> }
>>
>> - if (!test_and_clear_bit(IDE_AFLAG_IGNORE_DSC, &drive->atapi_flags) &&
>> - (stat & ATA_DSC) == 0) {
>> + /*
>> + * This is a precaution for IDE_AFLAG_IGNORE_DSC being conditionally set
>> + * above. We don't need a stronger enforcement of ordering because the
>> + * read below cannot precede the earlier write out-of-order since it is
>> + * to the same location. Also, since we have the ide port locked during
>> + * the ->do_request(), we only have to be aware of gcc reordering stuff.
>> + */
>> + barrier();
>
> Are you seeing a real problem with gcc here? No sane compiler should need
> a barrier() here (we would probably need zillions of them in kernel if it
> really does).
No, this is just a precaution. The asm I checked looked fine but since
the flag is set and right afterwards checked, it will be bad if this
somehow got reordered. I actually haven't checked whether anything like
that would be possible, at all.
--
Regards/Gruss,
Boris
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