linux-kernel - Re: [4/5] 2.6.21-rc5: known regressions

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Message-Id: <200703271209.14447.rjw@sisk.pl>
Date:	Tue, 27 Mar 2007 12:09:13 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Adrian Bunk <bunk@...sta.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, pavel@...e.cz,
	linux-pm@...ts.osdl.org, Thomas Meyer <thomas@...3r.de>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [4/5] 2.6.21-rc5: known regressions

On Tuesday, 27 March 2007 03:59, Adrian Bunk wrote:
> This email lists some known regressions in Linus' tree compared to 2.6.20.
> 
> If you find your name in the Cc header, you are either submitter of one
> of the bugs, maintainer of an affectected subsystem or driver, a patch
> of you caused a breakage or I'm considering you in any other way
> possibly involved with one or more of these issues.
> 
> Due to the huge amount of recipients, please trim the Cc when answering.

I think the following two:
 
> Subject    : suspend to disk: keypress required for power down
> References : http://lkml.org/lkml/2007/3/25/78
> Submitter  : Thomas Meyer <thomas@...3r.de>
> Status     : unknown
 
> Subject    : suspend to disk: non-boot cpus are disabled again
> References : http://lkml.org/lkml/2007/3/25/78
> Submitter  : Thomas Meyer <thomas@...3r.de>
> Handled-By : Rafael J. Wysocki <rjw@...k.pl>
>              Eric W. Biederman <ebiederm@...ssion.com>
> Status     : problem is being debugged

are related to the same issue.

The problem is that we call disable_nonboot_cpus() in swsusp before
powering down the system in order to avoid triggering the WARN_ON()
in arch/x86_64/kernel/acpi/sleep.c:init_low_mapping() and this doesn't
work well on Thomas' system.

Since the problem has been introduced by commit
94985134b7b46848267ed6b734320db01c974e72
(swsusp: disable nonboot CPUs before entering platform suspend), I think it's
better to revert this commit and remove the the WARN_ON() in
arch/x86_64/kernel/acpi/sleep.c:init_low_mapping() (appended is a patch that
removes the WARN_ON()).

Greetings,
Rafael


---
Remove the WARN_ON() in arch/x86_64/kernel/acpi/sleep.c:init_low_mapping(),
which triggers every time during the suspend to disk in the platform mode, as
the potential problem it is related to doesn't seem to occur in practice.

Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
 arch/x86_64/kernel/acpi/sleep.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: linux-2.6.21-rc5/arch/x86_64/kernel/acpi/sleep.c
===================================================================
--- linux-2.6.21-rc5.orig/arch/x86_64/kernel/acpi/sleep.c
+++ linux-2.6.21-rc5/arch/x86_64/kernel/acpi/sleep.c
@@ -66,8 +66,10 @@ static void init_low_mapping(void)
 {
 	pgd_t *slot0 = pgd_offset(current->mm, 0UL);
 	low_ptr = *slot0;
+	/* FIXME: We're playing with the current task's page tables here, which
+	 * is potentially dangerous on SMP systems.
+	 */
 	set_pgd(slot0, *pgd_offset(current->mm, PAGE_OFFSET));
-	WARN_ON(num_online_cpus() != 1);
 	local_flush_tlb();
 }
 
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