Re: [patch 10/10] mm: fix pagecache write deadlocks

[Nick Piggin]

Nick Piggin wrote:

> @@ -1878,31 +1889,88 @@ generic_file_buffered_write(struct kiocb
>  			break;
>  		}
>  
> +		/*
> +		 * non-uptodate pages cannot cope with short copies, and we
> +		 * cannot take a pagefault with the destination page locked.
> +		 * So pin the source page to copy it.
> +		 */
> +		if (!PageUptodate(page)) {
> +			unlock_page(page);
> +
> +			bytes = min(bytes, PAGE_CACHE_SIZE -
> +				     ((unsigned long)buf & ~PAGE_CACHE_MASK));
> +
> +			/*
> +			 * Cannot get_user_pages with a page locked for the
> +			 * same reason as we can't take a page fault with a
> +			 * page locked (as explained below).
> +			 */
> +			status = get_user_pages(current, current->mm,
> +					(unsigned long)buf & PAGE_CACHE_MASK, 1,
> +					0, 0, &src_page, NULL);

Thinko... get_user_pages needs to be called with mmap_sem held, obviously.

--
SUSE Labs, Novell Inc.
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