Re: [PATCH] mm: kmemleak: Skip check in kmemleak_*_phys when pfn bound is not ready

[patrick wang <patrick.wang.shcn@gmail.com>]

On Fri, May 27, 2022 at 11:25 AM <yee.lee@mediatek.com> wrote:
>
> From: Yee Lee <yee.lee@mediatek.com>
>
> In some archs (arm64), memblock allocates memory in boot time when
> the pfn boundary (max_pfn/min_pfn) is not ready. The lowmen checks in
> kmemleak_*_phys() drop those blocks and cause some false leak alarms
> on common kernel objects.

If I understand correctly, if those blocks are dropped, they will
not be added as kmemleak objects. So how could this affect
other objects?

Thanks,
Patrick

>
> Kmemleak output: (Qemu/arm64)
> unreferenced object 0xffff0000c0170a00 (size 128):
>   comm "swapper/0", pid 1, jiffies 4294892404 (age 126.208s)
>   hex dump (first 32 bytes):
>     62 61 73 65 00 00 00 00 00 00 00 00 00 00 00 00  base............
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<(____ptrval____)>] __kmalloc_track_caller+0x1b0/0x2e4
>     [<(____ptrval____)>] kstrdup_const+0x8c/0xc4
>     [<(____ptrval____)>] kvasprintf_const+0xbc/0xec
>     [<(____ptrval____)>] kobject_set_name_vargs+0x58/0xe4
>     [<(____ptrval____)>] kobject_add+0x84/0x100
>     [<(____ptrval____)>] __of_attach_node_sysfs+0x78/0xec
>     [<(____ptrval____)>] of_core_init+0x68/0x104
>     [<(____ptrval____)>] driver_init+0x28/0x48
>     [<(____ptrval____)>] do_basic_setup+0x14/0x28
>     [<(____ptrval____)>] kernel_init_freeable+0x110/0x178
>     [<(____ptrval____)>] kernel_init+0x20/0x1a0
>     [<(____ptrval____)>] ret_from_fork+0x10/0x20
>
> This patch relaxs the boundary checking in kmemleak_*_phys api
> if max_low_pfn is uninitialzed.
>
> Fixes: 23c2d4 (mm: kmemleak: take a full lowmem check in kmemleak_*_phy)
> Signed-off-by: Yee Lee <yee.lee@mediatek.com>
> ---
>  mm/kmemleak.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index a182f5ddaf68..6b2af544aa0f 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -1132,7 +1132,7 @@ EXPORT_SYMBOL(kmemleak_no_scan);
>  void __ref kmemleak_alloc_phys(phys_addr_t phys, size_t size, int min_count,
>                                gfp_t gfp)
>  {
> -       if (PHYS_PFN(phys) >= min_low_pfn && PHYS_PFN(phys) < max_low_pfn)
> +       if (!max_low_pfn || (PHYS_PFN(phys) >= min_low_pfn && PHYS_PFN(phys) < max_low_pfn))
>                 kmemleak_alloc(__va(phys), size, min_count, gfp);
>  }
>  EXPORT_SYMBOL(kmemleak_alloc_phys);
> @@ -1146,7 +1146,7 @@ EXPORT_SYMBOL(kmemleak_alloc_phys);
>   */
>  void __ref kmemleak_free_part_phys(phys_addr_t phys, size_t size)
>  {
> -       if (PHYS_PFN(phys) >= min_low_pfn && PHYS_PFN(phys) < max_low_pfn)
> +       if (!max_low_pfn || (PHYS_PFN(phys) >= min_low_pfn && PHYS_PFN(phys) < max_low_pfn))
>                 kmemleak_free_part(__va(phys), size);
>  }
>  EXPORT_SYMBOL(kmemleak_free_part_phys);
> @@ -1158,7 +1158,7 @@ EXPORT_SYMBOL(kmemleak_free_part_phys);
>   */
>  void __ref kmemleak_not_leak_phys(phys_addr_t phys)
>  {
> -       if (PHYS_PFN(phys) >= min_low_pfn && PHYS_PFN(phys) < max_low_pfn)
> +       if (!max_low_pfn || (PHYS_PFN(phys) >= min_low_pfn && PHYS_PFN(phys) < max_low_pfn))
>                 kmemleak_not_leak(__va(phys));
>  }
>  EXPORT_SYMBOL(kmemleak_not_leak_phys);
> @@ -1170,7 +1170,7 @@ EXPORT_SYMBOL(kmemleak_not_leak_phys);
>   */
>  void __ref kmemleak_ignore_phys(phys_addr_t phys)
>  {
> -       if (PHYS_PFN(phys) >= min_low_pfn && PHYS_PFN(phys) < max_low_pfn)
> +       if (!max_low_pfn || (PHYS_PFN(phys) >= min_low_pfn && PHYS_PFN(phys) < max_low_pfn))
>                 kmemleak_ignore(__va(phys));
>  }
>  EXPORT_SYMBOL(kmemleak_ignore_phys);
> --
> 2.18.0
>

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