linux-kernel - Re: [PATCH] dax: Split pmd map when fallback on COW

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Date:	Mon, 23 Nov 2015 15:58:46 -0700
From:	Toshi Kani <toshi.kani@....com>
To:	dan.j.williams@...el.com
Cc:	kirill.shutemov@...ux.intel.com, willy@...ux.intel.com,
	ross.zwisler@...ux.intel.com, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-nvdimm@...ts.01.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dax: Split pmd map when fallback on COW

On Mon, 2015-11-23 at 13:05 -0700, Toshi Kani wrote:
> An infinite loop of PMD faults was observed when attempted to
> mlock() a private read-only PMD mmap'd range of a DAX file.

Typo: the above description should be (remove "read-only"): 

An infinite loop of PMD faults was observed when attempted to mlock() a private
PMD mmap'd range of a DAX file.

-Toshi

> __dax_pmd_fault() simply returns with VM_FAULT_FALLBACK when
> falling back to PTE on COW.  However, __handle_mm_fault()
> returns without falling back to handle_pte_fault() because
> a PMD map is present in this case.
> 
> Change __dax_pmd_fault() to split the PMD map, if present,
> before returning with VM_FAULT_FALLBACK.

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