Re: [PATCH v6 01/10] mm: memblock: add missing HugeTLB flag name

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The patch adds 'RSV_HUGETLB' to the memblock debugfs flagname array, but the string is unreachable dead code. `memblock_debug_show()` iterates through the flags and breaks after printing the first matched (lowest) bit. Since `MEMBLOCK_RSRV_HUGETLB` (bit 7) is exclusively set alongside the lower-bit `MEMBLOCK_RSRV_KERN` (bit 5) flag, the loop always prints 'RSV_KERN' and breaks before reaching 'RSV_HUGETLB'.
--

commit 9e889d960694e60cb0ceee31e8dfe809d10a4085
Author: Meijing Zhao <zhaomeijing@lixiang.com>

mm: memblock: add missing HugeTLB flag name

This commit adds the missing "RSV_HUGETLB" entry to the memblock flagname
array so that debugfs can report the flag by name.

Link: https://lore.kernel.org/lkml/20260821020910.3428585-2-zhaomeijing100@gmail.com/

> diff --git a/mm/memblock.c b/mm/memblock.c
> index 9ce86349a29fa..f2952d725c10b 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
[ ... ]
> @@ -2886,6 +2886,7 @@ static const char * const flagname[] = {
>  	[ilog2(MEMBLOCK_RSRV_NOINIT)] = "RSV_NIT",
>  	[ilog2(MEMBLOCK_RSRV_KERN)] = "RSV_KERN",
>  	[ilog2(MEMBLOCK_KHO_SCRATCH)] = "KHO_SCRATCH",
> +	[ilog2(MEMBLOCK_RSRV_HUGETLB)] = "RSV_HUGETLB",
>  };
>  
>  static int memblock_debug_show(struct seq_file *m, void *private)

[Severity: Medium]
Will this new string ever be printed? 

Looking at memblock_debug_show(), it iterates through the flags from lowest
to highest bit and breaks after the first match:

mm/memblock.c:memblock_debug_show() {
    ...
            for (j = 0; j < count; j++) {
                if (reg->flags & (1U << j)) {
                    seq_printf(m, "%s\n", flagname[j]);
                    break;
                }
            }
    ...
}

And in memblock_alloc_hugetlb(), MEMBLOCK_RSRV_HUGETLB is allocated logically
ORed with MEMBLOCK_RSRV_KERN:

mm/memblock.c:memblock_alloc_hugetlb() {
    ...
        if (__memblock_reserve(addr, size, nid, 
                               MEMBLOCK_RSRV_KERN | MEMBLOCK_RSRV_HUGETLB))
    ...
}

Since MEMBLOCK_RSRV_KERN (bit 5) is lower than MEMBLOCK_RSRV_HUGETLB (bit 7),
does this mean the loop will always print "RSV_KERN" and break before reaching
"RSV_HUGETLB", making this addition effectively dead code?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260902073116.802752-1-chenwandun1@gmail.com?part=1