On Wed, Feb 12, 2025 at 11:17 PM Huacai Chen <chenhuacai@xxxxxxxxxxx> wrote:
>
> Hibernation assumes the memory layout after resume be the same as that
> before sleep, but CONFIG_RANDOM_KMALLOC_CACHES breaks this assumption.
[Let's also Cc SLAB ALLOCATOR folks in MAINTAINERS file]
Could you please elaborate what do you mean by
hibernation assumes 'the memory layout' after resume be the same as that
before sleep?
I don't understand how updating random_kmalloc_seed breaks resuming from
hibernation. Changing random_kmalloc_seed affects which kmalloc caches
newly allocated objects are from, but it should not affect the objects that are
already allocated (before hibernation).
> At least on LoongArch and ARM64 we observed failures of resuming from
> hibernation (on LoongArch non-boot CPUs fail to bringup, on ARM64 some
> devices are unusable).
Did you have any chance to reproduce it on x86_64?
> software_resume_initcall(), the function which resume the target kernel
> is a initcall function. So, move the random_kmalloc_seed initialisation
> after all initcalls.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 3c6152940584290668 ("Randomized slab caches for kmalloc()")
> Reported-by: Yuli Wang <wangyuli@xxxxxxxxxxxxx>
> Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> ---
>
> init/main.c | 3 +++
> mm/slab_common.c | 3 ---
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/init/main.c b/init/main.c
> index 2a1757826397..1362957bdbe4 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -1458,6 +1458,9 @@ static int __ref kernel_init(void *unused)
> /* need to finish all async __init code before freeing the memory */
> async_synchronize_full();
>
> +#ifdef CONFIG_RANDOM_KMALLOC_CACHES
> + random_kmalloc_seed = get_random_u64();
> +#endif
It doesn’t seem appropriate to put slab code in kernel_init.
Additionally, it introduces a dependency that the code must be executed
after all late_initcalls, which sounds like introducing yet another
type of initcall.
> system_state = SYSTEM_FREEING_INITMEM;
> kprobe_free_init_mem();
> ftrace_free_init_mem();
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 4030907b6b7d..23e324aee218 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -971,9 +971,6 @@ void __init create_kmalloc_caches(void)
> for (i = KMALLOC_SHIFT_LOW; i <= KMALLOC_SHIFT_HIGH; i++)
> new_kmalloc_cache(i, type);
> }
> -#ifdef CONFIG_RANDOM_KMALLOC_CACHES
> - random_kmalloc_seed = get_random_u64();
> -#endif
I have no idea how hibernation and resume work, but let me ask here:
Can we simply skip or defer updating random_kmalloc_seed when the system is
resuming from hibernation? (probably system_state represents this?)
> /* Kmalloc array is now usable */
> slab_state = UP;
--
Harry
