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Message-ID: <20080128103439.GC24010@elte.hu>
Date: Mon, 28 Jan 2008 11:34:39 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Yinghai Lu <Yinghai.Lu@....COM>
Cc: Mike Travis <travis@....com>, Christoph Lameter <clameter@....com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH] x86_64: mark x86_cpu_to_node_map_init to __initdata
like other xx_init
* Yinghai Lu <Yinghai.Lu@....COM> wrote:
> -int x86_cpu_to_node_map_init[NR_CPUS] = {
> +int x86_cpu_to_node_map_init[NR_CPUS] __initdata = {
> [0 ... NR_CPUS-1] = NUMA_NO_NODE
> };
i remember some linker warning here. While this array should indeed only
be used in early init, that decision is dynamic and our linker warnings
do not notice it. There's a special marker for such cases:
__initdata_refok. But ... i'm slightly nervous about turning off a vital
warning like that.
Sam, it would be nice to have a DEBUG_INITDATA mode of operation: in
this case free_initmem() would not truly free those pages but would
unmap them via:
kernel_map_pages(page, nrpages, 0);
could be made dependent on DEBUG_PAGEALLOC.
If this debugging is enabled then if any code references it, we get a
hard page fault. If we had a debug mode like that then bugs in this area
would not go unnoticed.
Or perhaps just make this part of normal DEBUG_PAGEALLOC. Like the patch
below on top of latest x86.git. Hm?
Ingo
------------------->
Subject: x86: init memory debugging
From: Ingo Molnar <mingo@...e.hu>
debug incorrect/late access to init memory, by permanently unmapping
the init memory ranges. Depends on CONFIG_DEBUG_PAGEALLOC=y.
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
arch/x86/mm/init_32.c | 12 ++++++++++++
arch/x86/mm/init_64.c | 11 +++++++++++
2 files changed, 23 insertions(+)
Index: linux-x86.q/arch/x86/mm/init_32.c
===================================================================
--- linux-x86.q.orig/arch/x86/mm/init_32.c
+++ linux-x86.q/arch/x86/mm/init_32.c
@@ -794,6 +794,18 @@ void free_init_pages(char *what, unsigne
unsigned long addr;
/*
+ * If debugging page accesses then do not free this memory but
+ * mark them not present - any buggy init-section access will
+ * create a kernel page fault:
+ */
+#ifdef CONFIG_DEBUG_PAGEALLOC
+ printk(KERN_INFO "debug: unmapping init memory %08lx..%08lx\n",
+ begin, PAGE_ALIGN(end));
+ set_memory_np(begin, (end - begin) >> PAGE_SHIFT);
+ return;
+#endif
+ set_memory_rw(begin, (end - begin) >> PAGE_SHIFT);
+ /*
* We just marked the kernel text read only above, now that
* we are going to free part of that, we need to make that
* writeable first.
Index: linux-x86.q/arch/x86/mm/init_64.c
===================================================================
--- linux-x86.q.orig/arch/x86/mm/init_64.c
+++ linux-x86.q/arch/x86/mm/init_64.c
@@ -580,6 +580,17 @@ void free_init_pages(char *what, unsigne
if (begin >= end)
return;
+ /*
+ * If debugging page accesses then do not free this memory but
+ * mark them not present - any buggy init-section access will
+ * create a kernel page fault:
+ */
+#ifdef CONFIG_DEBUG_PAGEALLOC
+ printk(KERN_INFO "debug: unmapping init memory %08lx..%08lx\n",
+ begin, PAGE_ALIGN(end));
+ set_memory_np(begin, (end - begin) >> PAGE_SHIFT);
+ return;
+#endif
printk(KERN_INFO "Freeing %s: %luk freed\n", what, (end - begin) >> 10);
for (addr = begin; addr < end; addr += PAGE_SIZE) {
--
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