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

[WANG Xuerui]

On 9/13/23 08:49, Huacai Chen wrote:
> 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().
Thanks for the clarification. According to the code behavior (and the 
comment I left on the reordering change below) I'm now sure the intended 
meaning is "calling memblock_reserve() after memblock_set_node() is 
effectively leaving those regions with nid=MAX_NUMNODES" (or something 
like that, pointing out that the memblock_set_node() call actually had 
no effect in this case). "Early" and "late" in the context of init code 
can be especially confusing IMO :-)
> 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/
--
WANG "xen0n" Xuerui

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