linux-kernel - Re: [PATCH v2] Do a proper locking for mmap and block size change

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Message-ID: <CA+55aFziCW_ywZACGoVyNSgy8mToAGhSbdo0VoUAaGvgSb2XxQ@mail.gmail.com>
Date:	Thu, 29 Nov 2012 09:19:30 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>, Jens Axboe <axboe@...nel.dk>,
	Jeff Chua <jeff.chua.linux@...il.com>,
	Lai Jiangshan <laijs@...fujitsu.com>, Jan Kara <jack@...e.cz>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2] Do a proper locking for mmap and block size change

On Wed, Nov 28, 2012 at 2:01 PM, Mikulas Patocka <mpatocka@...hat.com> wrote:
>
> This sounds sensible. I'm sending this patch.

This looks much better.

I think I'll apply this for 3.7 (since it's too late to do anything
fancier), and then for 3.8 I will rip out all the locking entirely,
because looking at the fs/buffer.c patch I wrote up, it's all totally
unnecessary.

Adding a ACCESS_ONCE() to the read of the i_blkbits value (when
creating new buffers) simply makes the whole locking thing pointless.
Just make the page lock protect the block size, and make it per-page,
and we're done.

No RCU grace period crap, no expedited mess, no nothing.

                      Linus
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