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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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