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

[Jiaxun Yang]

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?

In practical we run into uninitialized nid of reserved block problem, 
should we fix it
in our usage, or on memblock side?

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@xxxxxxxxxxx>
> ---
>   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