Re: [PATCH] memblock: exclude NOMAP regions from kmemleak

Anshuman Khandual
2021-10-19T04:21:35Z

On 10/13/21 11:17 AM, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
>
> Vladimir Zapolskiy reports:
>
> commit a7259df76702 ("memblock: make memblock_find_in_range method private")
> invokes a kernel panic while running kmemleak on OF platforms with nomaped
> regions:
>
> Unable to handle kernel paging request at virtual address fff000021e00000
> [...]
> scan_block+0x64/0x170
> scan_gray_list+0xe8/0x17c
> kmemleak_scan+0x270/0x514
> kmemleak_write+0x34c/0x4ac
>
> Indeed, NOMAP regions don't have linear map entries so an attempt to scan
> these areas would fault.
>
> Prevent such faults by excluding NOMAP regions from kmemleak.
>
> Link: https://lore.kernel.org/all/8ade5174-b143-d621-8c8e-dc6a1898c6fb@linaro.org
> Fixes: a7259df76702 ("memblock: make memblock_find_in_range method private")
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> Tested-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
> ---
> mm/memblock.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 184dcd2e5d99..5c3503c98b2f 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -936,7 +936,12 @@ int __init_memblock memblock_mark_mirror(phys_addr_t base, phys_addr_t size)
> */
> int __init_memblock memblock_mark_nomap(phys_addr_t base, phys_addr_t size)
> {
> - return memblock_setclr_flag(base, size, 1, MEMBLOCK_NOMAP);
> + int ret = memblock_setclr_flag(base, size, 1, MEMBLOCK_NOMAP);
> +
> + if (!ret)
> + kmemleak_free_part_phys(base, size);
> +
> + return ret;
> }
>
> /**
>
> base-commit: 64570fbc14f8d7cb3fe3995f20e26bc25ce4b2cc
>

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

A small nit though.

Just wondering. Should not the comment for memblock_mark_nomap() be
updated (or add a comment in the function) to explain the reason to
call kmemleak_free_part_phys(), to emphasize that a scan would fail
for such memory ranges due to lack of linear mapping ?