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From: Andrew Morton <akpm@linux-foundation.org>
To: Nick Piggin <npiggin@suse.de>
Cc: Linux Filesystems <linux-fsdevel@vger.kernel.org>,
	Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [patch 3/3] ext2: use perform_write aop
Date: Fri, 9 Feb 2007 11:14:55 -0800	[thread overview]
Message-ID: <20070209111455.67a69783.akpm@linux-foundation.org> (raw)
In-Reply-To: <20070208105508.26443.7806.sendpatchset@linux.site>

On Thu,  8 Feb 2007 14:07:46 +0100 (CET) Nick Piggin <npiggin@suse.de> 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.


  parent reply	other threads:[~2007-02-09 19:15 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-08 13:07 [rfc][patch 0/3] a faster buffered write deadlock fix? Nick Piggin
2007-02-08 13:07 ` [patch 1/3] fs: add an iovec iterator Nick Piggin
2007-02-08 19:49   ` Christoph Hellwig
2007-02-09  1:46     ` Nick Piggin
2007-02-09  2:03       ` Nate Diller
2007-02-09  3:31         ` Nick Piggin
2007-02-09 17:28           ` Zach Brown
2007-03-09 10:40         ` Christoph Hellwig
2007-02-08 23:04   ` Mark Fasheh
2007-02-08 13:07 ` [patch 2/3] fs: introduce perform_write aop Nick Piggin
2007-03-09 10:39   ` Christoph Hellwig
2007-03-09 12:52     ` Nick Piggin
2007-03-09 22:01       ` Anton Altaparmakov
2007-03-09 23:33     ` Mark Fasheh
2007-03-10  9:25       ` Christoph Hellwig
2007-03-12  2:13         ` Mark Fasheh
2007-03-14 13:30         ` Nick Piggin
2007-03-14 15:17           ` Christoph Hellwig
2007-02-08 13:07 ` [patch 3/3] ext2: use " Nick Piggin
2007-02-08 14:47   ` Dmitriy Monakhov
2007-02-09 19:14   ` Andrew Morton [this message]
2007-02-09 19:45     ` Andrew Morton
2007-02-10  1:34       ` Nick Piggin
2007-02-10  1:50         ` Andrew Morton
2007-02-09  0:38 ` [rfc][patch 0/3] a faster buffered write deadlock fix? Mark Fasheh
2007-02-09  2:04   ` Nick Piggin
2007-02-09  8:41 ` Andrew Morton
2007-02-09  9:54   ` Nick Piggin
2007-02-09 10:09     ` Andrew Morton
2007-02-09 10:32       ` Nick Piggin
2007-02-09 10:52         ` Andrew Morton
2007-02-09 11:31           ` Nick Piggin
2007-02-09 11:46             ` Andrew Morton
2007-02-09 12:11               ` Nick Piggin

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