Re: [PATCH v5 1/3] mm/memory-failure: Use a mutex to avoid memory_failure() races

[HORIGUCHI NAOYA(堀口 直也)]

On Sat, May 22, 2021 at 03:09:00PM -0700, Andrew Morton wrote:
> On Fri, 21 May 2021 12:01:54 +0900 Naoya Horiguchi <nao.horiguchi@xxxxxxxxx> wrote:
> 
> > There can be races when multiple CPUs consume poison from the same
> > page. The first into memory_failure() atomically sets the HWPoison
> > page flag and begins hunting for tasks that map this page. Eventually
> > it invalidates those mappings and may send a SIGBUS to the affected
> > tasks.
> > 
> > But while all that work is going on, other CPUs see a "success"
> > return code from memory_failure() and so they believe the error
> > has been handled and continue executing.
> > 
> > Fix by wrapping most of the internal parts of memory_failure() in
> > a mutex.
> 
> We can reduce the scope of that mutex, which helps readability at least.

Thanks, this change is totally fine to me.

> 
> --- a/mm/memory-failure.c~mm-memory-failure-use-a-mutex-to-avoid-memory_failure-races-fix
> +++ a/mm/memory-failure.c
> @@ -1397,8 +1397,6 @@ out:
>  	return rc;
>  }
>  
> -static DEFINE_MUTEX(mf_mutex);
> -
>  /**
>   * memory_failure - Handle memory failure of a page.
>   * @pfn: Page Number of the corrupted page
> @@ -1425,6 +1423,7 @@ int memory_failure(unsigned long pfn, in
>  	int res = 0;
>  	unsigned long page_flags;
>  	bool retry = true;
> +	static DEFINE_MUTEX(mf_mutex);
>  
>  	if (!sysctl_memory_failure_recovery)
>  		panic("Memory failure on page %lx", pfn);
> _
>