linux-kernel - Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online

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Date:   Thu, 13 Jun 2019 14:42:42 -0400
From:   Qian Cai <cai@....pw>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] mm/hotplug: skip bad PFNs from
 pfn_to_online_page()

On Wed, 2019-06-12 at 12:37 -0700, Dan Williams wrote:
> On Wed, Jun 12, 2019 at 12:16 PM Qian Cai <cai@....pw> wrote:
> > 
> > The linux-next commit "mm/sparsemem: Add helpers track active portions
> > of a section at boot" [1] causes a crash below when the first kmemleak
> > scan kthread kicks in. This is because kmemleak_scan() calls
> > pfn_to_online_page(() which calls pfn_valid_within() instead of
> > pfn_valid() on x86 due to CONFIG_HOLES_IN_ZONE=n.
> > 
> > The commit [1] did add an additional check of pfn_section_valid() in
> > pfn_valid(), but forgot to add it in the above code path.
> > 
> > page:ffffea0002748000 is uninitialized and poisoned
> > raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
> > raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
> > page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
> > ------------[ cut here ]------------
> > kernel BUG at include/linux/mm.h:1084!
> > invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN PTI
> > CPU: 5 PID: 332 Comm: kmemleak Not tainted 5.2.0-rc4-next-20190612+ #6
> > Hardware name: Lenovo ThinkSystem SR530 -[7X07RCZ000]-/-[7X07RCZ000]-,
> > BIOS -[TEE113T-1.00]- 07/07/2017
> > RIP: 0010:kmemleak_scan+0x6df/0xad0
> > Call Trace:
> >  kmemleak_scan_thread+0x9f/0xc7
> >  kthread+0x1d2/0x1f0
> >  ret_from_fork+0x35/0x4
> > 
> > [1] https://patchwork.kernel.org/patch/10977957/
> > 
> > Signed-off-by: Qian Cai <cai@....pw>
> > ---
> >  include/linux/memory_hotplug.h | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> > index 0b8a5e5ef2da..f02be86077e3 100644
> > --- a/include/linux/memory_hotplug.h
> > +++ b/include/linux/memory_hotplug.h
> > @@ -28,6 +28,7 @@
> >         unsigned long ___nr = pfn_to_section_nr(___pfn);           \
> >                                                                    \
> >         if (___nr < NR_MEM_SECTIONS && online_section_nr(___nr) && \
> > +           pfn_section_valid(__nr_to_section(___nr), pfn) &&      \
> >             pfn_valid_within(___pfn))                              \
> >                 ___page = pfn_to_page(___pfn);                     \
> >         ___page;                                                   \
> 
> Looks ok to me:
> 
> Acked-by: Dan Williams <dan.j.williams@...el.com>
> 
> ...but why is pfn_to_online_page() a multi-line macro instead of a
> static inline like all the helper routines it invokes?

Sigh, probably because it is a mess over there.

memory_hotplug.h and mmzone.h are included each other. Converted it directly to
a static inline triggers compilation errors because mmzone.h was included
somewhere else and found pfn_to_online_page() needs things like
pfn_valid_within() and online_section_nr() etc which are only defined later in
mmzone.h.

Move pfn_to_online_page() into mmzone.h triggers errors below.

In file included from ./arch/x86/include/asm/page.h:76,
                 from ./arch/x86/include/asm/thread_info.h:12,
                 from ./include/linux/thread_info.h:38,
                 from ./arch/x86/include/asm/preempt.h:7,
                 from ./include/linux/preempt.h:78,
                 from ./include/linux/spinlock.h:51,
                 from ./include/linux/mmzone.h:8,
                 from ./include/linux/gfp.h:6,
                 from ./include/linux/slab.h:15,
                 from ./include/linux/crypto.h:19,
                 from arch/x86/kernel/asm-offsets.c:9:
./include/linux/memory_hotplug.h: In function ‘pfn_to_online_page’:
./include/asm-generic/memory_model.h:54:29: error: ‘vmemmap’ undeclared (first
use in this function); did you mean ‘mem_map’?
 #define __pfn_to_page(pfn) (vmemmap + (pfn))
                             ^~~~~~~
./include/asm-generic/memory_model.h:82:21: note: in expansion of macro
‘__pfn_to_page’
 #define pfn_to_page __pfn_to_page
                     ^~~~~~~~~~~~~
./include/linux/memory_hotplug.h:30:10: note: in expansion of macro
‘pfn_to_page’
   return pfn_to_page(pfn);
          ^~~~~~~~~~~
./include/asm-generic/memory_model.h:54:29: note: each undeclared identifier is
reported only once for each function it appears in
 #define __pfn_to_page(pfn) (vmemmap + (pfn))
                             ^~~~~~~
./include/asm-generic/memory_model.h:82:21: note: in expansion of macro
‘__pfn_to_page’
 #define pfn_to_page __pfn_to_page
                     ^~~~~~~~~~~~~
./include/linux/memory_hotplug.h:30:10: note: in expansion of macro
‘pfn_to_page’
   return pfn_to_page(pfn);
          ^~~~~~~~~~~
make[1]: *** [scripts/Makefile.build:112: arch/x86/kernel/asm-offsets.s] Error 1