Re: [PATCH 2/4] x86, memblock: Fix crashkernel allocation

Yinghai Lu
2010-10-05T23:05:53Z

On 10/05/2010 03:29 PM, H. Peter Anvin wrote:
> On 10/04/2010 02:57 PM, Yinghai Lu wrote:
>>
>> +#define DEFAULT_BZIMAGE_ADDR_MAX 0x37FFFFFF
>> static void __init reserve_crashkernel(void)
>> {
>> unsigned long long total_mem;
>> @@ -518,17 +519,28 @@ static void __init reserve_crashkernel(v
>> if (crash_base <= 0) {
>> const unsigned long long alignment = 16<<20; /* 16M */
>>
>> - crash_base = memblock_find_in_range(alignment, ULONG_MAX, crash_size,
>> - alignment);
>> + /*
>> + * Assume half crash_size is for bzImage
>> + * kexec want bzImage is below DEFAULT_BZIMAGE_ADDR_MAX
>> + */
>> + crash_base = memblock_find_in_range(alignment,
>> + DEFAULT_BZIMAGE_ADDR_MAX + crash_size/2,
>> + crash_size, alignment);
>> +
>> if (crash_base == MEMBLOCK_ERROR) {
>> - pr_info("crashkernel reservation failed - No suitable area found.\n");
>> - return;
>> + crash_base = memblock_find_in_range(alignment,
>> + ULONG_MAX, crash_size, alignment);
>> +
>> + if (crash_base == MEMBLOCK_ERROR) {
>> + pr_info("crashkernel reservation failed - No suitable area found.\n");
>> + return;
>> + }
>> }
>>
>
> Okay, this *really* doesn't make sense.
>
> It's bad enough that kexec doesn't know what memory is safe for it, but
> why the heck the heuristic that "half is for bzImage and the rest can go
> beyond the heuristic limit"?

kdump want that range half for bzImage or half for initrd.

and kexec only check if bzImage can be put under small range.

> Can't we at least simply cap the region to
> the default, unless the kexec system has passed in some knowable
> alternative?

+ crash_base = memblock_find_in_range(alignment,
+ DEFAULT_BZIMAGE_ADDR_MAX,
+ crash_size, alignment);

Furthermore, why bother having the "fallback" at all
> (certainly without having a message!?) If we don't get the memory area
> we need we're likely to randomly fail anyway.

if kexec is fixed to work with bzImage with 64bit entry...

>
> Let me be completely clear -- it's obvious from all of this that kexec
> is fundamentally broken by design: if kexec can't communicate the safe
> memory to use it's busted seven ways to Sunday and it needs to be fixed.
> However, in the meantime I can see capping the memory available to it
> as a temporary band-aid, but a fallback to picking random memory is
> nuts, especially on the motivation that "a future kexec version might be
> able to use it." If so, the "future kexec tools" should SAY SO.

ok, please check

[PATCH -v6] x86, memblock: Fix crashkernel allocation

Cai Qian found crashkernel is broken with x86 memblock changes
1. crashkernel=128M@32M always reported that range is used, even first kernel is small
no one use that range
2. always get following report when using "kexec -p"
Could not find a free area of memory of a000 bytes...
locate_hole failed

The root cause is that generic memblock_find_in_range() will try to get range from top_down.
But crashkernel do need from low and specified range.

Let's limit the target range with crash_base + crash_size to make sure that
We get exact range.

-v6: use DEFAULT_BZIMAGE_ADDR_MAX to limit area that could be used by bzImge.

Reported-and-Bisected-by: CAI Qian <caiqian@redhat.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
arch/x86/kernel/setup.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

Index: linux-2.6/arch/x86/kernel/setup.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/setup.c
+++ linux-2.6/arch/x86/kernel/setup.c
@@ -501,6 +501,7 @@ static inline unsigned long long get_tot
return total << PAGE_SHIFT;
}

+#define DEFAULT_BZIMAGE_ADDR_MAX 0x37FFFFFF
static void __init reserve_crashkernel(void)
{
unsigned long long total_mem;
@@ -518,8 +519,12 @@ static void __init reserve_crashkernel(v
if (crash_base <= 0) {
const unsigned long long alignment = 16<<20; /* 16M */

- crash_base = memblock_find_in_range(alignment, ULONG_MAX, crash_size,
- alignment);
+ /*
+ * kexec want bzImage is below DEFAULT_BZIMAGE_ADDR_MAX
+ */
+ crash_base = memblock_find_in_range(alignment,
+ DEFAULT_BZIMAGE_ADDR_MAX, crash_size, alignment);
+
if (crash_base == MEMBLOCK_ERROR) {
pr_info("crashkernel reservation failed - No suitable area found.\n");
return;
@@ -527,8 +532,8 @@ static void __init reserve_crashkernel(v
} else {
unsigned long long start;

- start = memblock_find_in_range(crash_base, ULONG_MAX, crash_size,
- 1<<20);
+ start = memblock_find_in_range(crash_base,
+ crash_base + crash_size, crash_size, 1<<20);
if (start != crash_base) {
pr_info("crashkernel reservation failed - memory is in use.\n");
return;