Re: [bisected] 2.6.31 regression: fails to boot as xen guest

[Pekka Enberg <penberg@cs.helsinki.fi>]

On Tue, 2009-08-25 at 21:58 +0300, Pekka Enberg wrote:
> On Tue, 2009-08-25 at 20:22 +0200, Arnd Hannemann wrote:
> > Pekka Enberg wrote:
> > > On Tue, 2009-08-25 at 19:49 +0200, Arnd Hannemann wrote:
> > >> Hi Pekka,
> > >>
> > >> Pekka Enberg wrote:
> > >>> On Tue, 2009-08-25 at 18:49 +0200, Arnd Hannemann wrote:
> > >>>>> Thanks for doing the bisect! Can we also see your .config
> > >>>>> also?
> > >>>> Config for -rc7 is attached. My bisect configs were based on
> > >>>> that
> > >>> Thanks! While we wait for the Xen people, you can try the
> > >>> following patch to see if we can narrow the bug down to
> > >>> trap_init().
> > >> Yes seems to be trap_init(). -rc7 with this patch applied boots up
> > >> to the prompt.
> > >
> > > Thanks for testing! Ingo, what do you think of the following patch?
> > > AFAICT, x86-32 is the only architecture playing with traps in
> > > mem_init() so this should be the safest fix for 2.6.31.
> > 
> > Hmm, -rc7 + this fix does not work for me :-/
> > Still hangs before any output...
> 
> Arnd, does this work for you?

Here's a version of the patch that actually compiles. :-)

			Pekka

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 13ffa5d..b6ff185 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -50,6 +50,7 @@ config X86
 	select HAVE_KERNEL_BZIP2
 	select HAVE_KERNEL_LZMA
 	select HAVE_ARCH_KMEMCHECK
+	select HAVE_ARCH_MEM_INIT_LATE if X86_32
 
 config OUTPUT_FORMAT
 	string
@@ -86,6 +87,10 @@ config STACKTRACE_SUPPORT
 config HAVE_LATENCYTOP_SUPPORT
 	def_bool y
 
+config HAVE_ARCH_MEM_INIT_LATE
+	def_bool y
+	depends on X86_32
+
 config FAST_CMPXCHG_LOCAL
 	bool
 	default y
diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 3cd7711..488ed4b 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -956,13 +956,17 @@ void __init mem_init(void)
 	BUG_ON(VMALLOC_START				>= VMALLOC_END);
 	BUG_ON((unsigned long)high_memory		> VMALLOC_START);
 
-	if (boot_cpu_data.wp_works_ok < 0)
-		test_wp_bit();
-
 	save_pg_dir();
 	zap_low_mappings(true);
 }
 
+void __init mem_init_late(void)
+{
+	/* Interrupts are enabled at this point. */
+	if (boot_cpu_data.wp_works_ok < 0)
+		test_wp_bit();
+}
+
 #ifdef CONFIG_MEMORY_HOTPLUG
 int arch_add_memory(int nid, u64 start, u64 size)
 {
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9a72cc7..eefcfbe 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1052,6 +1052,14 @@ extern void si_meminfo(struct sysinfo * val);
 extern void si_meminfo_node(struct sysinfo *val, int nid);
 extern int after_bootmem;
 
+#ifdef CONFIG_HAVE_ARCH_MEM_INIT_LATE
+extern void mem_init_late(void);
+#else
+static inline void mem_init_late(void)
+{
+}
+#endif
+
 #ifdef CONFIG_NUMA
 extern void setup_per_cpu_pageset(void);
 #else
diff --git a/init/main.c b/init/main.c
index 2d9d6bd..45d8dbd 100644
--- a/init/main.c
+++ b/init/main.c
@@ -643,6 +643,7 @@ asmlinkage void __init start_kernel(void)
 	set_gfp_allowed_mask(__GFP_BITS_MASK);
 
 	kmem_cache_init_late();
+	mem_init_late();
 
 	/*
 	 * HACK ALERT! This is early. We're enabling the console before