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

[Dave Young]

On 01/05/18 at 08:19am, Atsushi Kumagai wrote:
> >On 01/03/18 at 10:30am, Dave Young wrote:
> >> 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.
> 
> makedumpfile needs some fix anyway since some logic depend on the array length
> of mem_section. I'm trying to fix it referring to the crash's fix.

Hmm, a makedumpfile only fix is enough for this issue?

> 
> > I'll give priority to release v1.6.3 since the commit will not be included
> > in the supported kernel(4.14).
> 
> The kernel change was merged also into kernel 4.14.9, I'm working on this issue
> for the next release(v1.6.3).
> 
> Thanks,
> Atsushi Kumagai
> 
> >> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> >> index b3663896278e..122494364179 100644
> >> --- a/kernel/crash_core.c
> >> +++ b/kernel/crash_core.c
> >> @@ -410,10 +410,16 @@ static int __init crash_save_vmcoreinfo_init(void)
> >>  	VMCOREINFO_SYMBOL(contig_page_data);
> >>  #endif
> >>  #ifdef CONFIG_SPARSEMEM
> >> +#ifdef CONFIG_SPARSEMEM_EXTREME
> >> +	vmcoreinfo_append_str("SYMBOL(mem_section)=%lx\n",
> >> +			      (unsigned long)mem_section);
> >> +#else
> >>  	VMCOREINFO_SYMBOL(mem_section);
> >> +#endif
> >
> >	vmcoreinfo_append_str("SYMBOL(mem_section)=%lx\n",
> >				(unsigned long)mem_section);
> >
> >This is enough to cover both cases. mem_section is array name in non
> >SPARSEMEM_EXTREME case, so value of &mem_section == value of
> >mem_section.
> >
> >>  	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
> >>  	VMCOREINFO_STRUCT_SIZE(mem_section);
> >>  	VMCOREINFO_OFFSET(mem_section, section_mem_map);
> >> +
> >>  #endif
> >>  	VMCOREINFO_STRUCT_SIZE(page);
> >>  	VMCOREINFO_STRUCT_SIZE(pglist_data);
> >>
> >> >
> >> > vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
> >> >
> >> > The thing is that VMCOREINFO_SYMBOL will reference symbol. While
> >> > checking all exported symbol, all of them are array names. So here
> >> > the value of &array_name is equal to the address of the first element of
> >> > array. Now the first exception appeared, mem_section, which could be not
> >> > an array name, but a pointer pointing at the allocated memory.
> >> >
> >> > For this issue, we either change as Dave mentioned two options, or can
> >> > we adjust VMCOREINFO_SYMBOL(name)?
> >> >
> >> > >
> >> > >  static int __init crash_save_vmcoreinfo_init(void)
> >> > >  {
> >> > > @@ -410,10 +412,11 @@ static int __init crash_save_vmcoreinfo_init(void)
> >> > >  	VMCOREINFO_SYMBOL(contig_page_data);
> >> > >  #endif
> >> > >  #ifdef CONFIG_SPARSEMEM
> >> > > -	VMCOREINFO_SYMBOL(mem_section);
> >> > > +	VMCOREINFO_SYMBOL_HACK(mem_section);
> >> > >  	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
> >> > >  	VMCOREINFO_STRUCT_SIZE(mem_section);
> >> > >  	VMCOREINFO_OFFSET(mem_section, section_mem_map);
> >> > > +
> >> > >  #endif
> >> > >  	VMCOREINFO_STRUCT_SIZE(page);
> >> > >  	VMCOREINFO_STRUCT_SIZE(pglist_data);
> >> > >
> >> > >
> >> > > But probably we need this instead, but I can not test it because I do
> >> > > not know how to fix makedumpfile to use a _NUMBER instead of a SYMBOL.
> >> > > Thus bring up the issue, seeking for thoughts and discussion.
> >> > >
> >> > > diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> >> > > index b3663896278e..dfa2238e2c28 100644
> >> > > --- a/kernel/crash_core.c
> >> > > +++ b/kernel/crash_core.c
> >> > > @@ -410,10 +410,17 @@ static int __init crash_save_vmcoreinfo_init(void)
> >> > > 	VMCOREINFO_SYMBOL(contig_page_data);
> >> > >  #endif
> >> > >  #ifdef CONFIG_SPARSEMEM
> >> > > +#ifdef CONFIG_SPARSEMEM_EXTREME
> >> > > +	VMCOREINFO_NUMBER(mem_section);
> >> > > +#else
> >> > > 	VMCOREINFO_SYMBOL(mem_section);
> >> > > +#endif
> >> > > 	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
> >> > > 	VMCOREINFO_STRUCT_SIZE(mem_section);
> >> > > 	VMCOREINFO_OFFSET(mem_section, section_mem_map);
> >> > >
> >> > > [snip]
> >> > >
> >> > > Thanks
> >> > > Dave
> 
> 

Thanks
Dave