Re: HPET regression in 2.6.26 versus 2.6.25 -- found another user with the same regression

David Witbrodt
2008-08-20T17:42:58Z

*** FINALLY FOUND THE EXACT PROBLEM ***

I woke up this morning with a new idea. I wish I had thought of this
TWO WEEKS AGO!

Commit 3def3d6d essentially involves 2 different changes:

1. request_resource () is replaced by insert_resource()

2. code to add {code,data,bss}_resource to the iomem_resource tree
is moved out of e820_reserve_resources() and into setup_arch()
directly. [The actual call of e820_reserve_resources() is also
located in setup_arch().]

Since this is 2 separate changes, I went back to 700efc1b, just
before the commit introducing the regression (3def3d6d).

When I applied change #2 alone, and GOT A WORKING KERNEL!
===== BEGIN DIFF ================
diff --git a/arch/x86/kernel/e820_64.c b/arch/x86/kernel/e820_64.c
index a8694a3..e452bea 100644
--- a/arch/x86/kernel/e820_64.c
+++ b/arch/x86/kernel/e820_64.c
@@ -229,8 +229,7 @@ unsigned long __init e820_end_of_ram(void)
/*
* Mark e820 reserved areas as busy for the resource manager.
*/
-void __init e820_reserve_resources(struct resource *code_resource,
- struct resource *data_resource, struct resource *bss_resource)
+void __init e820_reserve_resources(void)
{
int i;
for (i = 0; i < e820.nr_map; i++) {
@@ -246,20 +245,6 @@ void __init e820_reserve_resources(struct resource *code_resource,
res->end = res->start + e820.map[i].size - 1;
res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
request_resource(&iomem_resource, res);
- if (e820.map[i].type == E820_RAM) {
- /*
- * We don't know which RAM region contains kernel data,
- * so we try it repeatedly and let the resource manager
- * test it.
- */
- request_resource(res, code_resource);
- request_resource(res, data_resource);
- request_resource(res, bss_resource);
-#ifdef CONFIG_KEXEC
- if (crashk_res.start != crashk_res.end)
- request_resource(res, &crashk_res);
-#endif
- }
}
}

diff --git a/arch/x86/kernel/setup_64.c b/arch/x86/kernel/setup_64.c
index 187f084..a0584ac 100644
--- a/arch/x86/kernel/setup_64.c
+++ b/arch/x86/kernel/setup_64.c
@@ -322,6 +322,11 @@ void __init setup_arch(char **cmdline_p)

finish_e820_parsing();

+ /* after parse_early_param, so could debug it */
+ insert_resource(&iomem_resource, &code_resource);
+ insert_resource(&iomem_resource, &data_resource);
+ insert_resource(&iomem_resource, &bss_resource);
+
early_gart_iommu_check();

e820_register_active_regions(0, 0, -1UL);
@@ -454,7 +459,7 @@ void __init setup_arch(char **cmdline_p)
/*
* We trust e820 completely. No explicit ROM probing in memory.
*/
- e820_reserve_resources(&code_resource, &data_resource, &bss_resource);
+ e820_reserve_resources();
e820_mark_nosave_regions();

/* request I/O space for devices used on all i[345]86 PCs */
diff --git a/include/asm-x86/e820_64.h b/include/asm-x86/e820_64.h
index 9e06c6e..ef653a4 100644
--- a/include/asm-x86/e820_64.h
+++ b/include/asm-x86/e820_64.h
@@ -23,8 +23,7 @@ extern void update_memory_range(u64 start, u64 size, unsigned old_type,
extern void setup_memory_region(void);
extern void contig_e820_setup(void);
extern unsigned long e820_end_of_ram(void);
-extern void e820_reserve_resources(struct resource *code_resource,
- struct resource *data_resource, struct resource *bss_resource);
+extern void e820_reserve_resources(void);
extern void e820_mark_nosave_regions(void);
extern int e820_any_mapped(unsigned long start, unsigned long end, unsigned type);
extern int e820_all_mapped(unsigned long start, unsigned long end, unsigned type);
===== END DIFF ================

As a separate experiment, I started over with a clean version of
700efc1b, then introduced the change from request_resource() to
insert_resource():
===== BEGIN DIFF ================
diff --git a/arch/x86/kernel/e820_64.c b/arch/x86/kernel/e820_64.c
index a8694a3..988195d 100644
--- a/arch/x86/kernel/e820_64.c
+++ b/arch/x86/kernel/e820_64.c
@@ -245,7 +245,7 @@ void __init e820_reserve_resources(struct resource *code_resource,
res->start = e820.map[i].addr;
res->end = res->start + e820.map[i].size - 1;
res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
- request_resource(&iomem_resource, res);
+ insert_resource(&iomem_resource, res);
if (e820.map[i].type == E820_RAM) {
/*
* We don't know which RAM region contains kernel data,
===== END DIFF ================

The kernel produced from the change HANGS!

I am very late for work, but just couldn't leave home until I posted
these results. My conclusion is that, somehow, the reordering of
adding {code,data,bss}_resource to the iomem_resource tree is doing
funky things to certain people's machines!

HTH!!!
Dave W.