Re: memblock_reserve for unadded region (was: [PATCH] MIPS: loongson64: fix boot failure)

[Mike Rapoport <rppt@kernel.org>]

On Mon, Jan 15, 2024 at 02:08:21PM +0000, Jiaxun Yang wrote:
> Hi mm folks,
> 
> Just a quick question, what is the expected behavior of memblock_reserve
> a region that is not added to memblock with memblock_add?
> 
> I'm unable to find any documentation about memblock_reserve in comments and
> boot-time-mm, but as per my understanding to the code, this should be a
> legit usage?

Yes, memblock allows reserving memory that was not added to memblock with
memblock_add().
 
> In practical we run into uninitialized nid of reserved block problem, should
> we fix it
> in our usage, or on memblock side?

Apparently it's a bug in memblock :(

If you revert 61167ad5fecd ("mm: pass nid to reserve_bootmem_region()")
does the issue disappear?
 
> Thanks
> 
> 在 2023/12/25 09:30, Huang Pei 写道:
> > Since commit 61167ad5fecd("mm: pass nid to reserve_bootmem_region()),
> > loongson64 booting failed with CONFIG_DEFERRED_STRUCT_PAGE_INIT like
> > this:
> > ----------------------------------------------------------------------
> >   Call Trace:
> >   [<ffffffff8235d088>] reserve_bootmem_region+0xa8/0x184
> >   [<ffffffff82333940>] memblock_free_all+0x104/0x2a8
> >   [<ffffffff8231d8e4>] mem_init+0x84/0x94
> >   [<ffffffff82330958>] mm_core_init+0xf8/0x308
> >   [<ffffffff82318c38>] start_kernel+0x43c/0x86c
> > 
> >   Code: 10400028  2402fff0  de420000 <dc432880> 0203182b 14600022
> >   64420070  00003025  24040003
> > 
> >   ---[ end trace 0000000000000000 ]---
> >   Kernel panic - not syncing: Attempted to kill the idle task!
> >   ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
> > ----------------------------------------------------------------------
> > 
> > The root cause is no memory region "0x0-0x1fffff" paired with
> > memory-reserved region "0x0-0x1fffff" and "0x0-0xfff", with "memblock
> > =debug":
> > 
> > ----------------------------------------------------------------------
> >    memory[0x0]     [0x0000000000200000-0x000000000effffff],
> >    0x000000000ee00000 bytes on node 0 flags: 0x0 !!!!here
> >    memory[0x1]     [0x0000000090000000-0x00000000fdffffff],
> >    0x000000006e000000 bytes on node 0 flags: 0x0
> >    memory[0x2]     [0x0000000100000000-0x000000027fffffff],
> >    0x0000000180000000 bytes on node 0 flags: 0x0
> >    memory[0x3]     [0x0000100000000000-0x000010000fffffff],
> >    0x0000000010000000 bytes on node 1 flags: 0x0
> >    memory[0x4]     [0x0000100090000000-0x000010027fffffff],
> >    0x00000001f0000000 bytes on node 1 flags: 0x0
> >    reserved.cnt  = 0x1f
> >    reserved[0x0]   [0x0000000000000000-0x000000000190c80a],
> >    0x000000000190c80b bytes flags: 0x0 !!!!oops 0x0-0x1fffff not in memory[0]
> >    reserved[0x1]   [0x000000000190c810-0x000000000190eea3],
> >    0x0000000000002694 bytes flags: 0x0
> > ----------------------------------------------------------------------
> > 
> > It caused memory-reserved region "0x0-0x1fffff" without valid node id
> > in "memblock_get_region_node" from "memmap_init_reserved_pages", lead to
> > "reserve_bootmem_region-> init_reserved_page -> early_pfn_to_nid()"
> > accessing "node_data" out of bound.
> > 
> > To fix this bug, we should remove unnecessary memory block reservation.
> > 
> > +. no need to reserve 0x0-0x1fffff below kernel loading address, since
> > it is not registered by "memblock_add_node"
> > 
> > +. no need to reserve 0x0-0xfff for exception handling if it is not
> > registered by "memblock_add" either.
> > 
> > Fixes: commit 61167ad5fecd("mm: pass nid to reserve_bootmem_region())
> > Signed-off-by: Huang Pei <huangpei@loongson.cn>
> > ---
> >   arch/mips/kernel/traps.c    | 3 ++-
> >   arch/mips/loongson64/numa.c | 2 --
> >   2 files changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
> > index 246c6a6b0261..9b632b4c10c3 100644
> > --- a/arch/mips/kernel/traps.c
> > +++ b/arch/mips/kernel/traps.c
> > @@ -2007,7 +2007,8 @@ unsigned long vi_handlers[64];
> >   void reserve_exception_space(phys_addr_t addr, unsigned long size)
> >   {
> > -	memblock_reserve(addr, size);
> > +	if(memblock_is_region_memory(addr, size))
> > +		memblock_reserve(addr, size);
> >   }
> >   void __init *set_except_vector(int n, void *addr)
> > diff --git a/arch/mips/loongson64/numa.c b/arch/mips/loongson64/numa.c
> > index 8f61e93c0c5b..0f516dde81da 100644
> > --- a/arch/mips/loongson64/numa.c
> > +++ b/arch/mips/loongson64/numa.c
> > @@ -130,8 +130,6 @@ static void __init node_mem_init(unsigned int node)
> >   			memblock_reserve((node_addrspace_offset | 0xfe000000),
> >   					 32 << 20);
> > -		/* Reserve pfn range 0~node[0]->node_start_pfn */
> > -		memblock_reserve(0, PAGE_SIZE * start_pfn);
> >   	}
> >   }
> 
> -- 
> ---
> Jiaxun Yang
> 

-- 
Sincerely yours,
Mike.