Re: Race between vmtruncate and mapped areas?

[Rik van Riel]

On Thu, 15 May 2003, Andrea Arcangeli wrote:

> --- x/include/linux/fs.h.~1~	2003-05-14 23:26:19.000000000 +0200
> +++ x/include/linux/fs.h	2003-05-15 02:35:57.000000000 +0200
> @@ -421,6 +421,8 @@ struct address_space {
>  	struct vm_area_struct	*i_mmap;	/* list of private mappings */
>  	struct vm_area_struct	*i_mmap_shared; /* list of shared mappings */
>  	spinlock_t		i_shared_lock;  /* and spinlock protecting it */
> +	int			truncate_sequence1; /* serialize ->nopage against truncate */
> +	int			truncate_sequence2; /* serialize ->nopage against truncate */

How about calling them truncate_start and truncate_end ?

> --- x/mm/vmscan.c.~1~	2003-05-14 23:26:12.000000000 +0200
> +++ x/mm/vmscan.c	2003-05-15 00:22:57.000000000 +0200
> @@ -165,11 +165,10 @@ drop_pte:
>  		goto drop_pte;
>  
>  	/*
> -	 * Anonymous buffercache pages can be left behind by
> +	 * Anonymous buffercache pages can't be left behind by
>  	 * concurrent truncate and pagefault.
>  	 */
> -	if (page->buffers)
> -		goto preserve;
> +	BUG_ON(page->buffers);

I wonder if there is nothing else that can leave behind
buffers in this way.

> +	mb(); /* spin_lock has inclusive semantics */
> +	if (unlikely(truncate_sequence != mapping->truncate_sequence1)) {
> +		struct inode *inode;

This code looks like it should work, but IMHO it is very subtle
so it should really get some documentation.