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SubjectRe: PATCH (for comment): ide-cd possible race in PIO mode
On Wed, Nov 17 2004, Alan Cox wrote:
> Working on tracing down Fedora bug #115458
> (https://bugzilla.redhat.com/bugzilla/process_bug.cgi) I found what
> appears to be a race between the IDE CD driver and the hardware status.
> It doesn't appear to explain the bug at all but it does look like a bug
> of itself
>
> When we issue an ide command the status bits don't become valid for
> 400nS. In the DMA case ide_execute_command handles this but in the PIO
> case we don't do the needed locking, use OUTBSYNC to avoid posting or
> delay. This means that in some situations we can execute the command
> handler in PIO mode before the command status bits are valid and the
> handler may read and act wrongly.
>
> --- drivers/ide/ide-cd.c~ 2004-11-17 14:08:42.950485320 +0000
> +++ drivers/ide/ide-cd.c 2004-11-17 14:08:42.951485168 +0000
> @@ -897,7 +897,10 @@
> return ide_started;
> } else {
> /* packet command */
> - HWIF(drive)->OUTB(WIN_PACKETCMD, IDE_COMMAND_REG);
> + spin_lock_irqsave(&ide_lock, flags);
> + HWIF(drive)->OUTBSYNC(WIN_PACKETCMD, IDE_COMMAND_REG);
> + ndelay(400);
> + spin_unlock_irqsave(&ide_lock, flags);
> return (*handler) (drive);
> }
> }

What good does the lock do?

--
Jens Axboe

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