linux-kernel - Re: [PATCH] ia64/mm: fix a bad_page bug when crash kernel booting

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Date:	Mon, 04 Feb 2013 16:32:45 +0000
From:	Matt Fleming <matt.fleming@...el.com>
To:	Xishi Qiu <qiuxishi@...wei.com>
Cc:	"Luck, Tony" <tony.luck@...el.com>, fenghua.yu@...el.com,
	Liujiang <jiang.liu@...wei.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] ia64/mm: fix a bad_page bug when crash kernel booting

On Tue, 2013-01-29 at 11:52 +0800, Xishi Qiu wrote:
> On ia64 platform, I set "crashkernel=1024M-:600M", and dmesg shows 128M-728M
> memory is reserved for crash kernel. Then "echo c > /proc/sysrq-trigger" to
> test kdump.
> 
> When crash kernel booting, efi_init() will aligns the memory address in
> IA64_GRANULE_SIZE(16M), so 720M-728M memory will be dropped, It means
> crash kernel only manage 128M-720M memory.
> 
> But initrd start and end are fixed in boot loader, it is before efi_init(),
> so initrd size maybe overflow when free_initrd_mem().

[...]

> diff --git a/arch/ia64/mm/init.c b/arch/ia64/mm/init.c
> index b755ea9..cfdb1eb 100644
> --- a/arch/ia64/mm/init.c
> +++ b/arch/ia64/mm/init.c
> @@ -207,6 +207,17 @@ free_initrd_mem (unsigned long start, unsigned long end)
>  	start = PAGE_ALIGN(start);
>  	end = end & PAGE_MASK;
> 
> +	/*
> +	 * Initrd size is fixed in boot loader, but kernel parameter max_addr
> +	 * which aligns in granules is fixed after boot loader, so initrd size
> +	 * maybe overflow.
> +	 */
> +	if (max_addr != ~0UL) {
> +		end = GRANULEROUNDDOWN(end);
> +		if (start > end)
> +			start = end;
> +	}
> +
>  	if (start < end)
>  		printk(KERN_INFO "Freeing initrd memory: %ldkB freed\n", (end - start) >> 10);

I don't think this is the correct fix.

Now, my ia64-fu is weak, but could it be that there's actually a bug in
efi_init() and that the following patch would be the best way to fix
this?

---

diff --git a/arch/ia64/kernel/efi.c b/arch/ia64/kernel/efi.c
index f034563..8d579f1 100644
--- a/arch/ia64/kernel/efi.c
+++ b/arch/ia64/kernel/efi.c
@@ -482,7 +482,7 @@ efi_init (void)
 		if (memcmp(cp, "mem=", 4) == 0) {
 			mem_limit = memparse(cp + 4, &cp);
 		} else if (memcmp(cp, "max_addr=", 9) == 0) {
-			max_addr = GRANULEROUNDDOWN(memparse(cp + 9, &cp));
+			max_addr = GRANULEROUNDUP(memparse(cp + 9, &cp));
 		} else if (memcmp(cp, "min_addr=", 9) == 0) {
 			min_addr = GRANULEROUNDDOWN(memparse(cp + 9, &cp));
 		} else {


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