makedumpfile saving vmcore fails with dynamically allocated mem_section (was: Re: [PATCH] handle renamed init_level4_pgt -> init_top_pgt)

[Dave Young]

On 01/03/18 at 03:21pm, Dave Anderson wrote:
> 
> 
> ----- Original Message -----
> 
> > On 01/02/18 at 05:08pm, Baoquan He wrote:
> > > On 01/02/18 at 04:57pm, Dave Young wrote:
> > > > The root cause is this commit makes mem_section as a pointer instead of
> > > > the static array.
> > > > 
> > > > VMCOREINFO_SYMBOL() expand it as &mem_section, this is not correct in
> > > > the test case any more.
> > > > 
> > > > This hack code works for me:
> > > > 
> > > > diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> > > > index b3663896278e..f5fe6068ae39 100644
> > > > --- a/kernel/crash_core.c
> > > > +++ b/kernel/crash_core.c
> > > > @@ -376,6 +376,8 @@ phys_addr_t __weak paddr_vmcoreinfo_note(void)
> > > >  {
> > > >  	return __pa(vmcoreinfo_note);
> > > >  }
> > > > +#define VMCOREINFO_SYMBOL_HACK(name) \
> > > > +	vmcoreinfo_append_str("SYMBOL(%s)=%lx\n", #name, (unsigned long)name)
> > > 
> > > Oh, you made a new one. We may use vmcoreinfo_append_str directly since
> > > there's an existing one in crash_save_vmcoreinfo():
> > 
> > Yes, it should be something like this instead, this should ensure
> > makedumpfile maybe crash tool works without any modifications,
> > waiting for feedback from Atsushi, also ccing Dave for crash utility
> > potential issue.
> 
> Yeah, I ran into that issue when testing 4.15, and fixed it upstream:
> 
>   https://github.com/crash-utility/crash/commit/264f22dafe9f37780c4113fd08e8d5b2138edbce
> 
>   commit 264f22dafe9f37780c4113fd08e8d5b2138edbce
>   Author: Dave Anderson <anderson at redhat.com>
>   Date:   Wed Nov 29 15:28:41 2017 -0500
> 
>     Fix for Linux 4.15 and later kernels that are configured with
>     CONFIG_SPARSEMEM_EXTREME, and that contain kernel commit
>     83e3c48729d9ebb7af5a31a504f3fd6aff0348c4, titled "mm/sparsemem:
>     Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y".
>     Without the patch, kernels configured with SPARSEMEM_EXTREME
>     have changed the data type of "mem_section" from an array to
>     a pointer, leading to errors in commands such as "kmem -p",
>     "kmem -n", "kmem -s", and any other command that translates a
>     physical address to its page struct address.
>     (anderson at redhat.com)
> 

Hi Dave,

I tried latest crash tool, but segment fault happened, I put the
vmlinux/vmcore in below url, could you have a look?:
http://people.redhat.com/ruyang/rhbz1528542/127.0.0.1-2018-01-05-10:29:23/

---
crash 7.2.0++
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WARNING: could not find MAGIC_START!
WARNING: kernel version inconsistency between vmlinux and dumpfile

please wait... (gathering task table data)      
WARNING: duplicate idle tasks?

WARNING: duplicate idle tasks?
please wait... (determining panic task)    
WARNING: active task ffffffff81e90536 on cpu 0 not found in PID hash

[ 1156.567444] crash[2964]: segfault at 7175228 ip 00000000004bf39e sp 00007ffd5dce3f30 error 6 in crash[400000+6da000]
Segmentation fault (core dumped)

The tested kernel applied below patch (a tuned patch according to bhe's
suggestion):

---
 kernel/crash_core.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- linux.orig/kernel/crash_core.c
+++ linux/kernel/crash_core.c
@@ -410,7 +410,8 @@ static int __init crash_save_vmcoreinfo_
 	VMCOREINFO_SYMBOL(contig_page_data);
 #endif
 #ifdef CONFIG_SPARSEMEM
-	VMCOREINFO_SYMBOL(mem_section);
+	vmcoreinfo_append_str("SYMBOL(mem_section)=%lx\n",
+			      (unsigned long)mem_section);
 	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
 	VMCOREINFO_STRUCT_SIZE(mem_section);
 	VMCOREINFO_OFFSET(mem_section, section_mem_map);


Thanks
Dave