Re: [PATCH] LoongArch: Set all reserved memblocks on Node#0 at initialization

[Huacai Chen]

On Wed, Sep 13, 2023 at 12:08 AM WANG Xuerui <kernel@xxxxxxxxxx> wrote:
>
> On 9/11/23 17:28, Huacai Chen wrote:
> > After commit 61167ad5fecdea ("mm: pass nid to reserve_bootmem_region()")
> > we get a panic if DEFERRED_STRUCT_PAGE_INIT is enabled:
> >
> > [snip]
> >
> > The reason is early memblock_reserve() in memblock_init() set node id
> Why is it that only "early" but not "late" memblock_reserve() matters? I
> failed to see the reason because the arch-specific memblock_init() isn't
> even in the backtrace, which means that *neither* is the culprit.
Late memblock_reserve() operates on subregions of memblock.memory
regions. These reserved regions will be set to the correct node at the
first iteration of memmap_init_reserved_pages().

Huacai

> > to MAX_NUMNODES, which causes NODE_DATA(nid) be a NULL dereference in
> "making NODE_DATA(nid) a NULL ..."
> > reserve_bootmem_region() -> init_reserved_page(). So set all reserved
> > memblocks on Node#0 at initialization to avoid this panic.
> >
> > Reported-by: WANG Xuerui <git@xxxxxxxxxx>
> > Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> > ---
> >   arch/loongarch/kernel/mem.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/loongarch/kernel/mem.c b/arch/loongarch/kernel/mem.c
> > index 4a4107a6a965..aed901c57fb4 100644
> > --- a/arch/loongarch/kernel/mem.c
> > +++ b/arch/loongarch/kernel/mem.c
> > @@ -50,7 +50,6 @@ void __init memblock_init(void)
> >       }
> >
> >       memblock_set_current_limit(PFN_PHYS(max_low_pfn));
> > -     memblock_set_node(0, PHYS_ADDR_MAX, &memblock.memory, 0);
> >
> >       /* Reserve the first 2MB */
> >       memblock_reserve(PHYS_OFFSET, 0x200000);
> > @@ -58,4 +57,7 @@ void __init memblock_init(void)
> >       /* Reserve the kernel text/data/bss */
> >       memblock_reserve(__pa_symbol(&_text),
> >                        __pa_symbol(&_end) - __pa_symbol(&_text));
> > +
> > +     memblock_set_node(0, PHYS_ADDR_MAX, &memblock.memory, 0);
> > +     memblock_set_node(0, PHYS_ADDR_MAX, &memblock.reserved, 0);
> So the reordering is for being able to override the newly added
> memblocks' nids to 0, and additionally doing the same for
> memblock.reserved is the actual fix. Looks okay.
> >   }
>
> And I've tested the patch on the 2-way 3C5000L server, and it now
> correctly boots with deferred struct page init enabled. Thanks for
> providing such a quick fix!
>
> Tested-by: WANG Xuerui <git@xxxxxxxxxx>
> Reviewed-by: WANG Xuerui <git@xxxxxxxxxx>  # with nits addressed
>
> --
> WANG "xen0n" Xuerui
>
> Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/
>
>