Messages in this thread | | | Date | Mon, 22 Nov 2004 08:58:02 +0100 | From | Jens Axboe <> | Subject | Re: PATCH (for comment): ide-cd possible race in PIO mode |
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On Wed, Nov 17 2004, Jens Axboe wrote: > 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); > > }
btw alan, have you attempted to compile this? It averages 2 errors out of 4 lines :)
-- Jens Axboe
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