Subject: Re: lockdep warning while booting POWER9 PowerNV

From: Michael Ellerman <[email-masked]>
Date: Thu, 05 Sep 2019 13:55:35 +1000

Bart Van Assche <[email-masked]> writes:
> On 8/30/19 2:13 PM, Qian Cai wrote:
>> https://raw.githubusercontent.com/cailca/linux-mm/master/powerpc.config
>> 
>> Once in a while, booting an IBM POWER9 PowerNV system (8335-GTH) would generate
>> a warning in lockdep_register_key() at,
>> 
>> if (WARN_ON_ONCE(static_obj(key)))
>> 
>> because
>> 
>> key = 0xc0000000019ad118
>> &_stext = 0xc000000000000000
>> &_end = 0xc0000000049d0000
>> 
>> i.e., it will cause static_obj() returns 1.
>
> (back from a trip)
>
> Hi Qian,
>
> Does this mean that on POWER9 it can happen that a dynamically allocated 
> object has an address that falls between &_stext and &_end?

I thought that was true on all arches due to initmem, but seems not.

I guess we have the same problem as s390 and we need to define
arch_is_kernel_initmem_freed().

Qian, can you try this:

diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
index 4a1664a8658d..616b1b7b7e52 100644
--- a/arch/powerpc/include/asm/sections.h
+++ b/arch/powerpc/include/asm/sections.h
@@ -5,8 +5,22 @@
 
 #include <linux/elf.h>
 #include <linux/uaccess.h>
+
+#define arch_is_kernel_initmem_freed arch_is_kernel_initmem_freed
+
 #include <asm-generic/sections.h>
 
+extern bool init_mem_is_free;
+
+static inline int arch_is_kernel_initmem_freed(unsigned long addr)
+{
+	if (!init_mem_is_free)
+		return 0;
+
+	return addr >= (unsigned long)__init_begin &&
+		addr < (unsigned long)__init_end;
+}
+
 extern char __head_end[];
 
 #ifdef __powerpc64__

cheers