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Date: Mon, 11 Feb 2008 11:37:15 +0900 From: Tejun Heo <htejun@...il.com> To: linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org, htejun@...il.com, alan@...hat.com, jeff@...zik.org Subject: Re: [PATCH] libata: Forcing PIO0 mode on reset must not freeze system Hello, Holger Macht wrote: > Calling ap->ops->set_piomode(ap, dev) on a device/controller which got > already removed, locks the system hard. Reproducibly on an X60 attached to > a dock station containing a cdrom device with doing > > $ echo 1 > /sys/devices/platform/dock.0/undock && echo 123 > /dev/sr0 > > This calls ata_eh_reset(...) which in turn tries to force PIO mode 0. But > the device is already gone. > > Bisecting revealed the following commit as culprit: > > commit cdeab1140799f09c5f728a5ff85e0bdfa5679cd2 > Author: Tejun Heo <htejun@...il.com> > Date: Mon Oct 29 16:41:09 2007 +0900 > > libata: relocate forcing PIO0 on reset > > Forcing PIO0 on reset was done inside ata_bus_softreset(), which is a > bit out of place as it should be applied to all resets - hard, soft > and implementation which don't use ata_bus_softreset(). Relocate it > such that... > > * For new EH, it's done in ata_eh_reset() before calling prereset. > > * For old EH, it's done before calling ap->ops->phy_reset() in > ata_bus_probe(). > > This makes PIO0 forced after all resets. Another difference is that > reset itself is done after PIO0 is forced. > > Signed-off-by: Tejun Heo <htejun@...il.com> > Acked-by: Alan Cox <alan@...hat.com> > Signed-off-by: Jeff Garzik <jeff@...zik.org> > > > ATTENTION! The following patch solves the problem on my system, but please > be aware that I don't really know what I'm doing because I don't have the > big picture. There's surely a better way to check if the device/controller > is still functional than calling ata_link_{online,offline}. In the above example, even the reset sequence itself can cause hang if the hardware is implemented slightly differently. The reason why set_piomode() locks up but reset sequence doesn't is simple dumb luck. I think the proper fix is to tell libata to detach the cdrom before undocking. > Signed-off-by: Holger Macht <hmacht@...e.de> NACK. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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