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