linux-kernel - Re: [3/5] 2.6.21-rc4: known regressions (v2)

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Date:	Sun, 25 Mar 2007 06:56:08 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Thomas Meyer <thomas@...3r.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-pci@...ey.karlin.mff.cuni.cz,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Tony Luck <tony.luck@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <lenb@...nel.org>
Subject: Re: [3/5] 2.6.21-rc4: known regressions (v2)

"Rafael J. Wysocki" <rjw@...k.pl> writes:

> Yes, in kernel/power/disk.c:power_down() .
>
> Please comment out the disable_nonboot_cpus() in there and retest (but please
> test the latest Linus' tree).

<rant>

Why do we even need a disable_nonboot_cpus in that path?  machine_shutdown
on i386 and x86_64 should take care of that.  Further the code that computes
the boot cpu is bogus (not all architectures require cpu == 0 to be
the boot cpu), and disabling non boot cpus appears to be a strong
x86ism, in the first place.

If the only reason for disable_nonboot_cpus there is to avoid the
WARN_ON in init_low_mappings() we should seriously consider killing
it.  If we can wait for 2.6.22 the relocatable x86_64 patchset that
Andi has queued, has changes that kill the init_low_mapping() hack.

I'm not very comfortable with calling cpu_down in a common code path
right now either.  I'm fairly certain we still don't have that
correct.  So if we confine the mess that is cpu_down to #if
defined(CPU_HOTPLUG) && defined(CONFIG_EXPERIMENTAL) I don't care.
If we start using it everywhere I'm very nervous.  I know the irq
migration when bringing a cpu down is strongly racy, and I don't think
we actually put cpus to sleep properly either.

</rant>

Eric
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