[PATCH 0/3 v5] dax: some dax fixes and cleanups

[Boaz Harrosh <boaz@plexistor.com>]

Hi Andrew

I finally had the time to beat up these fixes based on linux-next/akpm
and it looks OK.
I'm sending the two fix patches with @stable + a patch-1 for the 4.0
Kernel. The 4.1-rc Kernel will need a different patch.

It is your call if you want these in stable. It is a breakage in the dax
code that went into 4.0. But I guess it will not have that many users right
at the get go. So feel free to remove the CC:@stable. (Also the old XIP that
this DAX changed had all the same problems)

[v5]
* A new patch-1 Based on linux-next/akpm branch because mm/memory.c
  completely changed there.
  Also a 4.0 version of the same patch-1 if needed for stable@

List of patches:
 [PATCH 1/3] mm(v4.1): New pfn_mkwrite same as page_mkwrite for VM_PFNMAP
 [PATCH 2/3] dax: use pfn_mkwrite to update c/mtime + freeze
 [PATCH 3/3] dax: Unify ext2/4_{dax,}_file_operations

	All these patches are based on linux-next/akpm. I'm not sure how
	it will interact with ext4-next though.

 [PATCH 1/3 @stable] mm(v4.0): New pfn_mkwrite same as page_mkwrite for VM_PFNMAP

	This patch is for 4.0 based tree if we decide to send
	[PATCH 2/3] to stable.


[v4] dax: some dax fixes and cleanups
* First patch fixed according to Andrew's comments. Thanks Andrew.
  1st and 2nd patch can go into current Kernel as they fix something
  that was merged this release.
* Added a new patch to fix up splice in the dax case, and cleanup.
  This one can wait for 4.1 (Also the first two not that anyone uses dax
  in production.)
* DAX freeze is not fixed yet. As we have more problems then I originally
  hoped for, as pointed out by Dave.
  (Just as a referance I'm sending a NO-GOOD additional patch to show what
   is not good enough to do. Was the RFC of [v3])
* Not re-posting the xfstest Dave please pick this up (It already found bugs
  in none dax FSs)

[v3] dax: Fix mmap-write not updating c/mtime
* I'm re-posting the two DAX patches that fix the mmap-write after read
  problem with DAX. (No changes since [v2])
* I'm also posting a 3rd RFC patch to address what Jan said about fs_freeze
  and making mapping read-only. 
  Jan Please review and see if this is what you meant.

[v2]
Jan Kara has pointed out that if we add the
sb_start/end_pagefault pair in the new pfn_mkwrite we
are then fixing another bug where: A user could start
writing to the page while filesystem is frozen.

[v1]
The main problem is that current mm/memory.c will no call us with page_mkwrite
if we do not have an actual page mapping, which is what DAX uses.
The solution presented here introduces a new pfn_mkwrite to solve this problem.
Please see patch-2 for details.

I've been running with this patch for 4 month both HW and VMs with no apparent
danger, but see patch-1 I played it safe.

I am also posting an xfstest 080 that demonstrate this problem, I believe
that also some git operations (can't remember which) suffer from this problem.
Actually Eryu Guan found that this test fails on some other FS as well.

Matthew hi
I would love to have your ACK on these patches?

Thanks
Boaz