Hi,
On Tuesday 02 June 2009 09:05:07 Borislav Petkov wrote:
> There are two sites where the flag is being changed: ide_retry_pc
> and idetape_do_request. Both codepaths are protected by hwif->busy
> (ide_lock_port) and therefore we shouldn't need the atomic accesses. The
> only problem would be the compiler reordering the accesses, therefore the
> optimization barrier.
>
> Spotted-by: Jiri Slaby <jirislaby@xxxxxxxxx>
> Signed-off-by: Borislav Petkov <petkovbb@xxxxxxxxx>
[...]
> --- 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).
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