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SubjectRe: percpu related boot crash on x86 (was: Linux 2.6.38-rc1)

* Tejun Heo <tj@kernel.org> wrote:

> Hello,
>
> On Wed, Jan 19, 2011 at 02:56:23PM +0200, Pekka Enberg wrote:
> > Is vmalloc() and vfree() supposed to work with interrupts disabled? I
> > always thought they weren't which would mean something in
> > pcpu_mem_alloc() needs changing...
>
> They aren't but percpu allocator doesn't call them with interrupts
> disabled normally. It only happens during early boot before it's
> enabled for the first time but this is an allowed exception. We'll
> probably need to update the WARN_ON to consider the rare call path.
> It also looks like something in that path is turning off/on IRQ
> instead of saving/restoring it, so that probably needs to be changed
> too but both aren't really critical.
>
> I think the real problem is a lot of unsigned int percpu allocations
> added by 6c9ae009 (irq: use per_cpu kstat_irqs). percpu allocator
> should be able to cope but it assumes that it would always be able to
> allocate contiguous allocation map using vmalloc and that might be
> failing, although I cannot readily see how or why that would happen
> frequently on a 64bit machine.

Btw., based on Peter's suggestion i tried the limit-bumping hack below - but it did
not help, the crash still triggers on 5%-10% of all randconfig bootups.

Thanks,

Ingo

From e2c013d28c8fe81cd30976dcd3058cc86c6285d3 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Wed, 19 Jan 2011 20:15:20 +0100
Subject: [PATCH] <not for upstream> percpu: Increase allocation limits

Might solve the boot crashes ...

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
mm/percpu.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/mm/percpu.c b/mm/percpu.c
index 3f93001..5cd9cf4 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -74,7 +74,7 @@
#include <asm/io.h>

#define PCPU_SLOT_BASE_SHIFT 5 /* 1-31 shares the same slot */
-#define PCPU_DFL_MAP_ALLOC 16 /* start a map with 16 ents */
+#define PCPU_DFL_MAP_ALLOC 64 /* start a map with 64 ents */

#ifdef CONFIG_SMP
/* default addr <-> pcpu_ptr mapping, override in asm/percpu.h if necessary */

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