Messages in this thread | | | From | Bartlomiej Zolnierkiewicz <> | Subject | Re: [PATCH 1/2] ide-tape: change IDE_AFLAG_IGNORE_DSC non-atomically | Date | Tue, 2 Jun 2009 12:18:33 +0200 |
| |
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@gmail.com> > Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
[...]
> --- 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).
| |