linux-kernel - Re: [PATCH 0/2] fix for direct-I/O to DAX mappings

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Message-ID: <20170302134513.zwkfse3j3vjhzy55@XZHOUW.usersys.redhat.com>
Date:   Thu, 2 Mar 2017 21:45:13 +0800
From:   Xiong Zhou <xzhou@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     akpm@...ux-foundation.org, x86@...nel.org,
        Xiong Zhou <xzhou@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux-mm@...ck.org, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        torvalds@...ux-foundation.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH 0/2] fix for direct-I/O to DAX mappings

On Sat, Feb 25, 2017 at 09:08:28AM -0800, Dan Williams wrote:
> Hi Andrew,
> 
> While Ross was doing a review of a new mmap+DAX direct-I/O test case for
> xfstests, from Xiong, he noticed occasions where it failed to trigger a
> page dirty event.  Dave then spotted the problem fixed by patch1. The
> pte_devmap() check is precluding pte_allows_gup(), i.e. bypassing
> permission checks and dirty tracking.

This mmap-dax-dio case still fails with this patchset, while it makes
sense. It's the test case that need to be fixed.

BTW, this patchset fixes another xfsrestore issue, which i hit now
and then, xfs/301 w/ or wo/ DAX only on nvdimms. xfsrestore never
return but killable.

Thanks,
> 
> Patch2 is a cleanup and clarifies that pte_unmap() only needs to be done
> once per page-worth of ptes. It unifies the exit paths similar to the
> generic gup_pte_range() in the __HAVE_ARCH_PTE_SPECIAL case.
> 
> I'm sending this through the -mm tree for a double-check from memory
> management folks. It has a build success notification from the kbuild
> robot.
> 
> ---
> 
> Dan Williams (2):
>       x86, mm: fix gup_pte_range() vs DAX mappings
>       x86, mm: unify exit paths in gup_pte_range()
> 
> 
>  arch/x86/mm/gup.c |   37 +++++++++++++++++++++----------------
>  1 file changed, 21 insertions(+), 16 deletions(-)