On Thu, 8 Feb 2007 14:07:46 +0100 (CET) Nick Piggin <[email protected]> wrote:
> +void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
> +{
> + unsigned int block_start, block_end;
> + struct buffer_head *head, *bh;
> +
> + BUG_ON(!PageLocked(page));
> + if (!page_has_buffers(page))
> + return;
> +
> + bh = head = page_buffers(page);
> + block_start = 0;
> + do {
> + block_end = block_start + bh->b_size;
> +
> + if (buffer_new(bh)) {
> + if (block_end > from && block_start < to) {
> + if (!PageUptodate(page)) {
> + unsigned start, end;
> + void *kaddr;
> +
> + start = max(from, block_start);
> + end = min(to, block_end);
> +
> + kaddr = kmap_atomic(page, KM_USER0);
> + memset(kaddr+start, 0, block_end-end);
> + flush_dcache_page(page);
> + kunmap_atomic(kaddr, KM_USER0);
> + set_buffer_uptodate(bh);
> + }
I don't see how this differs from the previous attempts to solve the
deadlock via atomic copt_from_user(). Here we temporarily zero out the
pagecache page then block_perform_write() unlocks the page. So another
thread can come in, read the page and see the temporary zeroes?
If so, that might be preventable by leaving the buffer nonuptodate.
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