Re: [PATCH] Fix races in 2.4.2-ac22 SysV shared memory

[Christoph Rohland]

Hi Stephen,

On Fri, 23 Mar 2001, Stephen C. Tweedie wrote:
> @@ -234,11 +243,11 @@
>  		return -ENOMEM;
>  	}
>  
> -	spin_lock(&info->lock);
> -	shmem_recalc_inode(page->mapping->host);
>  	entry = shmem_swp_entry(info, page->index); 
>	if (IS_ERR(entry)) /* this had been allocted on page allocation */
>  		BUG();
> +	spin_lock(&info->lock);
> +	shmem_recalc_inode(page->mapping->host);
>  	error = -EAGAIN;
>  	if (entry->val) {
>  		__swap_free(swap, 2);

I think this is wrong. The spinlock protects us against
shmem_truncate. shmem_swp_entry cannot sleep in this case since the
entry is allocated in nopage.

Greetings
		Christoph