Re: [PATCH] cramfs corruption after BLKFLSBUF on loop device

Andrew Morton
2006-06-01T21:21:13Z

Olaf Hering <olh@suse.de> wrote:
>
>
>
> +/* return a page in PageUptodate state, BLKFLSBUF may have flushed the page */
> +static struct page *cramfs_read_cache_page(struct address_space *m, unsigned int n)
> +{
> + struct page *page;
> + int readagain = 5;
> +retry:
> + page = read_cache_page(m, n, (filler_t *)m->a_ops->readpage, NULL);
> + if (IS_ERR(page))
> + return NULL;
> + lock_page(page);
> + if (PageUptodate(page))
> + return page;
> + unlock_page(page);
> + page_cache_release(page);
> + if (readagain--)
> + goto retry;
> + return NULL;
> +}

Better, but it's still awful, isn't it? The things you were discussing
with Chris look more promising. PG_Dirty would be a bit of a hack, but at
least it'd be a 100% reliable hack, whereas the above is a
whatever-the-previous-failure-rate-was-to-the-fifth hack.

> + page = cramfs_read_cache_page(mapping, blocknr + i);
> + if (page) {
> + memcpy(data, kmap_atomic(page, KM_USER0), PAGE_CACHE_SIZE);
> + kunmap(page);

kunmap_atomic, please.

> + unlock_page(page);
> + page_cache_release(page);
> + } else
> + memset(data, 0, PAGE_CACHE_SIZE);
> + }
> data += PAGE_CACHE_SIZE;
> }
> return read_buffers[buffer] + offset;