linux-kernel - Re: [PATCH 2/2] dax: fix bdev NULL pointer dereferences

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Date:	Tue, 2 Feb 2016 17:46:42 +0100
From:	Jan Kara <jack@...e.cz>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-nvdimm <linux-nvdimm@...1.01.org>
Subject: Re: [PATCH 2/2] dax: fix bdev NULL pointer dereferences

On Tue 02-02-16 08:33:56, Dan Williams wrote:
> On Tue, Feb 2, 2016 at 3:17 AM, Jan Kara <jack@...e.cz> wrote:
> [..]
> > I see, thanks for explanation. So I'm OK with changing what is stored in
> > the radix tree to accommodate this use case but my reservation that we IHMO
> > have other more pressing things to fix remains...
> 
> We don't need pfns in the radix to support XFS RT configurations.
> Just call get_blocks() again and use the sector, or am I missing
> something?

You are correct. But if you decide to pay the cost of additional
get_block() call, you only need the dirty tag in the radix tree and nothing
else. So my understanding was that the whole point of games with radix tree
is avoiding this extra get_block() calls for fsync().

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR