linux-kernel - Re: SATA resume slowness, e1000 MSI warning

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Date:	Fri, 09 Mar 2007 20:41:14 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Kok, Auke" <auke-jan.h.kok@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Jeff Garzik <jeff@...zik.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Michael S. Tsirkin" <mst@...lanox.co.il>,
	Pavel Machek <pavel@....cz>,
	Jens Axboe <jens.axboe@...cle.com>,
	Adrian Bunk <bunk@...sta.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, linux-pm@...ts.osdl.org,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>
Subject: Re: SATA resume slowness, e1000 MSI warning

"Kok, Auke" <auke-jan.h.kok@...el.com> writes:

> Eric W. Biederman wrote:
>
> [CHOP]
>
>> Below is an additional set of warnings that should help debug this.
>> The old code just got lucky that it triggered a warning when this happens.
>
>
> I'm trying this patch together with the other 2 that you sent out a few days
> ago. I'm seeing some minor issues with this and lots of bogus warnings as far as
> I can see.
>
> If I suspend/resume and unload e1000, then reinsert e1000.ko, I immediately hit
> the WARN_ON at `msi.c:516: WARN_ON(!hlist_empty(&dev->saved_cap_space));`
>
> I'm not sure that's useful debugging information. even though saved state exists
> the module has been removed, so you might want to purge the state table when the
> driver gets removed?
>
>
> anyway, back to testing.

Sorry I should have been clear.

With the last two patches I sent out:
pci: Repair pci_save/restore_state so we can restore one save many times.
msi: Safer state caching.

Those WARN_ON's are now totally bogus.  

In essence the WARN_ON's were testing to ensure pci_save_state and
pci_restore_state were paired.

The assumptions was that pci_restore_state would remove everything
from the list that pci_save_state placed on it.

When I reworked the code and removed the bogus pairing requirement it meant
that if we ever save state and have a pci-e or pci-x capability we will have
a state structure on the list until the kernel reboots. 

In summary:
pci_save_state and pci_restore_state were making a wrong assumption
about the world.  The WARN_ON patch tested to ensure the world matched
those functions.  When I fixed those functions to match the world the
WARN_ON's became completely bogus.

Eric
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