linux-kernel - Re: [RESEND][PATCH] 9p: add write-cache support to loose cache mode

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Date:	Wed, 14 Feb 2007 14:05:44 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Eric Van Hensbergen <ericvh@...il.com>,
	linux-kernel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net
Subject: Re: [RESEND][PATCH] 9p: add write-cache support to loose cache mode

Andrew Morton wrote:
>>On Tue, 13 Feb 2007 20:07:44 -0600 "Eric Van Hensbergen" <ericvh@...il.com> wrote:
>>On 2/13/07, Andrew Morton <akpm@...ux-foundation.org> wrote:
>>
>>>>On Tue, 13 Feb 2007 17:55:31 -0600 Eric Van Hensbergen <ericvh@...il.com> wrote:
>>>>+int v9fs_prepare_write(struct file *file, struct page *page,
>>>>+                    unsigned from, unsigned to)
>>>>+{
>>>>+     if (!PageUptodate(page)) {
>>>>+             if (to - from != PAGE_CACHE_SIZE) {
>>>>+                     void *kaddr = kmap_atomic(page, KM_USER0);
>>>>+                     memset(kaddr, 0, from);
>>>>+                     memset(kaddr + to, 0, PAGE_CACHE_SIZE - to);
>>>>+                     flush_dcache_page(page);
>>>>+                     kunmap_atomic(kaddr, KM_USER0);
>>>>+             }
>>>>+             SetPageUptodate(page);
>>>>+     }
>>>
>>>This will mark the page uptodate while the piece between `to' and `from' is
>>>uninitialised.  A concurrent pagefault can come in and permit a read of
>>>that uninitialised data.  Because filemap_nopage() doesn't lock the page if
>>>it is uptodate.
>>>
>>
>>Okay - I snagged this code from fs/libfs.c (simple_prepare_write) --
>>is that code also not correct, or am I just using it in the wrong
>>context?
>>
> 
> 
> libfs.c is wrong.  Nick has fixes, but they got tangled up in other stuff.

Yeah. 1/9 in that series should be applied on its own and sent upstream.

Need me to resend?

-- 
SUSE Labs, Novell Inc.
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