linux-ext4 - Re: [PATCH] ext2, ext4: Fix issue with missing journal entry

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Message-ID: <20160224204446.GB13473@linux.intel.com>
Date:	Wed, 24 Feb 2016 13:44:46 -0700
From:	Ross Zwisler <ross.zwisler@...ux.intel.com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
	Theodore Ts'o <tytso@....edu>,
	Dan Williams <dan.j.williams@...el.com>,
	Jan Kara <jack@...e.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-ext4@...r.kernel.org, linux-nvdimm@...ts.01.org
Subject: Re: [PATCH] ext2, ext4: Fix issue with missing journal entry

On Thu, Jan 28, 2016 at 09:32:11AM -0700, Ross Zwisler wrote:
> On Thu, Jan 28, 2016 at 02:16:30PM +0100, Jan Kara wrote:
> > On Wed 27-01-16 12:01:48, Ross Zwisler wrote:
> > > As it is currently written ext4_dax_mkwrite() assumes that the call into
> > > __dax_mkwrite() will not have to do a block allocation so it doesn't create
> > > a journal entry.  For a read that creates a zero page to cover a hole
> > > followed by a write that actually allocates storage this is incorrect.  The
> > > ext4_dax_mkwrite() -> __dax_mkwrite() -> __dax_fault() path calls
> > > get_blocks() to allocate storage.
> > > 
> > > Fix this by having the ->page_mkwrite fault handler call ext4_dax_fault()
> > > as this function already has all the logic needed to allocate a journal
> > > entry and call __dax_fault().
> > > 
> > > Also update the ext2 fault handlers in this same way to remove duplicate
> > > code and keep the logic between ext2 and ext4 the same.
> > > 
> > > Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> > 
> > Ah, ok, you are right. The patch looks good but Matthew is reworking the
> > area more (so ext4_da_mkwrite() is likely to return) so it this worth it?
> > Or do you expect Matthew's patches to land much later?
> 
> Yep, Matthew is in the process of reworking all of the DAX fault handling.
> 
> I was thinking that we might want to take this patch for v4.5, since it fixes
> a bug that I'm guessing could lead to some sort of corruption (lack of a
> journal entry entry for an allocating write), and then Matthew's reworks would
> land in v4.6?

Hey Jan,

Looks like this patch didn't ever get merged for v4.5?  Is it still queued for
v4.6?

Thanks,
- Ross
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