Messages in this thread Patch in this message | | | Date | Thu, 24 Mar 2011 20:13:18 +0200 (EET) | From | Pekka Enberg <> | Subject | Re: [GIT PULL] SLAB changes for v2.6.39-rc1 |
| |
Hi Ingo,
On Thu, 24 Mar 2011, Ingo Molnar wrote: > * Pekka Enberg <penberg@kernel.org> wrote: > >> On Thu, Mar 24, 2011 at 4:41 PM, Christoph Lameter <cl@linux.com> wrote: >>> On Thu, 24 Mar 2011, Ingo Molnar wrote: >>> >>>> FYI, some sort of boot crash has snuck upstream in the last 24 hours: >>>> >>>> BUG: unable to handle kernel paging request at ffff87ffc147e020 >>>> IP: [<ffffffff811aa762>] this_cpu_cmpxchg16b_emu+0x2/0x1c >>> >>> Hmmm.. This is the fallback code for the case that the processor does not >>> support cmpxchg16b. >> >> How does alternative_io() work? Does it require >> alternative_instructions() to be executed. If so, the fallback code >> won't be active when we enter kmem_cache_init(). Is there any reason >> check_bugs() is called so late during boot? Can we do something like >> the totally untested attached patch? > > Does the config i sent you boot on your box? I think the bug is pretty generic > and should trigger on any box.
Here's a patch that reorganizes the alternatives fixup to happen earlier so that the fallback should work. It boots on my machine so please give it a spin if possible.
I'll try out your .config next.
Pekka
From dd1534455196d2a8f6c9c912db614e59986c9f0e Mon Sep 17 00:00:00 2001 From: Pekka Enberg <penberg@kernel.org> Date: Thu, 24 Mar 2011 19:59:35 +0200 Subject: [PATCH] x86: Early boot alternative instructions
Commit 8a5ec0ba42c4919e2d8f4c3138cc8b987fdb0b79 ("Lockless (and preemptless) fastpaths for slub") added use of cmpxchg16b in kmem_cache_init() which happens early on during the boot. As cmpxchg16b is not supported on some older AMD CPUs, there's a alternative_io() fallback for cmpxchg16b emulation.
Unfortunately alternative_instructions() happens late in the boot sequence so the fallback code is not patched into kernel text which causes the following oops:
BUG: unable to handle kernel paging request at ffff87ffc147e020 IP: [<ffffffff811aa762>] this_cpu_cmpxchg16b_emu+0x2/0x1c
[<ffffffff810d9cbc>] ? kmem_cache_alloc+0x4c/0x110 [<ffffffff8151cf06>] kmem_cache_init+0xeb/0x2b0 [<ffffffff81504a06>] start_kernel+0x1de/0x49b [<ffffffff8150432b>] x86_64_start_reservations+0x132/0x136 [<ffffffff81504140>] ? early_idt_handlers+0x140/0x140
This patch reorganizes the code so that alternative_io() tagged fallbacks are patched to the kernel before kmem_cache_init() is called.
Reported-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Pekka Enberg <penberg@kernel.org> --- arch/x86/include/asm/alternative.h | 1 + arch/x86/kernel/alternative.c | 12 +++++++++++- arch/x86/kernel/cpu/bugs.c | 2 -- arch/x86/kernel/cpu/bugs_64.c | 2 -- include/asm-generic/alternative.h | 19 +++++++++++++++++++ init/main.c | 3 +++ 6 files changed, 34 insertions(+), 5 deletions(-) create mode 100644 include/asm-generic/alternative.h
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h index 13009d1..ca819c6 100644 --- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -54,6 +54,7 @@ struct alt_instr { #endif };
+extern void alternative_instructions_early(void); extern void alternative_instructions(void); extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 4a23467..32e96dd 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -453,7 +453,7 @@ extern struct paravirt_patch_site __start_parainstructions[], __stop_parainstructions[]; #endif /* CONFIG_PARAVIRT */
-void __init alternative_instructions(void) +void __init alternative_instructions_early(void) { /* The patching is not fully atomic, so try to avoid local interruptions that might execute the to be patched code. @@ -473,6 +473,16 @@ void __init alternative_instructions(void)
apply_alternatives(__alt_instructions, __alt_instructions_end);
+ restart_nmi(); +} + +void __init alternative_instructions(void) +{ + /* The patching is not fully atomic, so try to avoid local interruptions + that might execute the to be patched code. + Other CPUs are not running. */ + stop_nmi(); + /* switch to patch-once-at-boottime-only mode and free the * tables in case we know the number of CPUs will never ever * change */ diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index c39576c..3854e58 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -15,7 +15,6 @@ #include <asm/i387.h> #include <asm/msr.h> #include <asm/paravirt.h> -#include <asm/alternative.h>
static int __init no_halt(char *s) { @@ -165,5 +164,4 @@ void __init check_bugs(void) check_popad(); init_utsname()->machine[1] = '0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86); - alternative_instructions(); } diff --git a/arch/x86/kernel/cpu/bugs_64.c b/arch/x86/kernel/cpu/bugs_64.c index 04f0fe5..1064db5 100644 --- a/arch/x86/kernel/cpu/bugs_64.c +++ b/arch/x86/kernel/cpu/bugs_64.c @@ -5,7 +5,6 @@
#include <linux/kernel.h> #include <linux/init.h> -#include <asm/alternative.h> #include <asm/bugs.h> #include <asm/processor.h> #include <asm/mtrr.h> @@ -18,7 +17,6 @@ void __init check_bugs(void) printk(KERN_INFO "CPU: "); print_cpu_info(&boot_cpu_data); #endif - alternative_instructions();
/* * Make sure the first 2MB area is not mapped by huge pages diff --git a/include/asm-generic/alternative.h b/include/asm-generic/alternative.h new file mode 100644 index 0000000..893a070 --- /dev/null +++ b/include/asm-generic/alternative.h @@ -0,0 +1,19 @@ +/* + * linux/include/asm-generic/alternative.h + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ +#ifndef __ASM_GENERIC_ALTERNATIVE_H__ +#define __ASM_GENERIC_ALTERNATIVE_H__ + +static inline void alternative_instructions_early(void) +{ +} + +static inline void alternative_instructions(void) +{ +} + +#endif /* __ASM_GENERIC_ALTERNATIVE_H__ */ diff --git a/init/main.c b/init/main.c index 4a9479e..0bb3c52 100644 --- a/init/main.c +++ b/init/main.c @@ -74,6 +74,7 @@ #include <asm/setup.h> #include <asm/sections.h> #include <asm/cacheflush.h> +#include <asm/alternative.h>
#ifdef CONFIG_X86_LOCAL_APIC #include <asm/smp.h> @@ -508,6 +509,7 @@ asmlinkage void __init start_kernel(void) vfs_caches_init_early(); sort_main_extable(); trap_init(); + alternative_instructions_early(); mm_init(); /* * Set up the scheduler prior starting any interrupts (such as the @@ -614,6 +616,7 @@ asmlinkage void __init start_kernel(void) taskstats_init_early(); delayacct_init();
+ alternative_instructions(); check_bugs();
acpi_early_init(); /* before LAPIC and SMP init */ -- 1.7.0.4 | |