Re: [PATCH v3 2/2] mm, hwpoison: When copy-on-write hits poison, take page offline

[Miaohe Lin]

On 2022/10/22 4:01, Tony Luck wrote:
> Cannot call memory_failure() directly from the fault handler because
> mmap_lock (and others) are held.

Could you please explain which lock makes it unfeasible to call memory_failure() directly and
why? I'm somewhat confused. But I agree using memory_failure_queue() should be a good idea.

> 
> It is important, but not urgent, to mark the source page as h/w poisoned
> and unmap it from other tasks.
> 
> Use memory_failure_queue() to request a call to memory_failure() for the
> page with the error.
> 
> Also provide a stub version for CONFIG_MEMORY_FAILURE=n
> 
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
>  include/linux/mm.h | 5 ++++-
>  mm/memory.c        | 4 +++-
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 8bbcccbc5565..03ced659eb58 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3268,7 +3268,6 @@ enum mf_flags {
>  int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
>  		      unsigned long count, int mf_flags);
>  extern int memory_failure(unsigned long pfn, int flags);
> -extern void memory_failure_queue(unsigned long pfn, int flags);
>  extern void memory_failure_queue_kick(int cpu);
>  extern int unpoison_memory(unsigned long pfn);
>  extern int sysctl_memory_failure_early_kill;
> @@ -3277,8 +3276,12 @@ extern void shake_page(struct page *p);
>  extern atomic_long_t num_poisoned_pages __read_mostly;
>  extern int soft_offline_page(unsigned long pfn, int flags);
>  #ifdef CONFIG_MEMORY_FAILURE
> +extern void memory_failure_queue(unsigned long pfn, int flags);
>  extern int __get_huge_page_for_hwpoison(unsigned long pfn, int flags);
>  #else
> +static inline void memory_failure_queue(unsigned long pfn, int flags)
> +{
> +}
>  static inline int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
>  {
>  	return 0;
> diff --git a/mm/memory.c b/mm/memory.c
> index b6056eef2f72..eae242351726 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2866,8 +2866,10 @@ static inline int __wp_page_copy_user(struct page *dst, struct page *src,
>  	unsigned long addr = vmf->address;
>  
>  	if (likely(src)) {
> -		if (copy_mc_user_highpage(dst, src, addr, vma))
> +		if (copy_mc_user_highpage(dst, src, addr, vma)) {
> +			memory_failure_queue(page_to_pfn(src), 0);

It seems MF_ACTION_REQUIRED is not needed for memory_failure_queue() here. Thanks for your patch.

Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>

Thanks,
Miaohe Lin