linux-kernel - Re: [PATCH 1/2] ide-tape: change IDE_AFLAG_IGNORE

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Message-ID: <20090603053916.GA3577@liondog.tnic>
Date:	Wed, 3 Jun 2009 07:39:16 +0200
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
Cc:	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] ide-tape: change IDE_AFLAG_IGNORE_DSC
	non-atomically

Hi,

> > > 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.
> 
> Please remove it then.

---

From: Borislav Petkov <petkovbb@...il.com>
Date: Mon, 1 Jun 2009 13:43:49 +0200
Subject: [PATCH 1/2] ide-tape: change IDE_AFLAG_IGNORE_DSC non-atomically

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.

Spotted-by: Jiri Slaby <jirislaby@...il.com>
Signed-off-by: Borislav Petkov <petkovbb@...il.com>
---
 drivers/ide/ide-atapi.c |    2 +-
 drivers/ide/ide-tape.c  |   12 +++++++-----
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/ide/ide-atapi.c b/drivers/ide/ide-atapi.c
index afe5a43..fbcb851 100644
--- a/drivers/ide/ide-atapi.c
+++ b/drivers/ide/ide-atapi.c
@@ -258,7 +258,7 @@ void ide_retry_pc(ide_drive_t *drive)
 	pc->req_xfer = sense_rq->data_len;
 
 	if (drive->media == ide_tape)
-		set_bit(IDE_AFLAG_IGNORE_DSC, &drive->atapi_flags);
+		drive->atapi_flags |= IDE_AFLAG_IGNORE_DSC;
 
 	if (ide_queue_sense_rq(drive, pc))
 		ide_complete_rq(drive, -EIO, blk_rq_bytes(drive->hwif->rq));
diff --git a/drivers/ide/ide-tape.c b/drivers/ide/ide-tape.c
index 203bbea..f1d3c7b 100644
--- a/drivers/ide/ide-tape.c
+++ b/drivers/ide/ide-tape.c
@@ -656,15 +656,15 @@ 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) {
+	if (!(drive->atapi_flags & IDE_AFLAG_IGNORE_DSC) &&
+	    !(stat & ATA_DSC)) {
 		if (postponed_rq == NULL) {
 			tape->dsc_polling_start = jiffies;
 			tape->dsc_poll_freq = tape->best_dsc_rw_freq;
@@ -684,7 +684,9 @@ static ide_startstop_t idetape_do_request(ide_drive_t *drive,
 			tape->dsc_poll_freq = IDETAPE_DSC_MA_SLOW;
 		idetape_postpone_request(drive);
 		return ide_stopped;
-	}
+	} else
+		drive->atapi_flags &= ~IDE_AFLAG_IGNORE_DSC;
+
 	if (rq->cmd[13] & REQ_IDETAPE_READ) {
 		pc = &tape->queued_pc;
 		ide_tape_create_rw_cmd(tape, pc, rq, READ_6);
-- 
1.6.3.1


-- 
Regards/Gruss,
    Boris.
--
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