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Date: Fri, 15 Apr 2016 21:55:19 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Matthew Wilcox <willy@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andres Lagar-Cavilla <andreslc@google.com>,
        Yang Shi <yang.shi@linaro.org>, Ning Qu <quning@gmail.com>,
        David Rientjes <rientjes@google.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH 09/10] huge pagecache: mmap_sem is unlocked when
 truncation splits pmd
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On Thu, 14 Apr 2016 13:39:22 -0400 Matthew Wilcox <willy@linux.intel.com> wrote:

> On Tue, Apr 05, 2016 at 01:55:23PM -0700, Hugh Dickins wrote:
> > zap_pmd_range()'s CONFIG_DEBUG_VM !rwsem_is_locked(&mmap_sem) BUG()
> > will be invalid with huge pagecache, in whatever way it is implemented:
> > truncation of a hugely-mapped file to an unhugely-aligned size would
> > easily hit it.
> 
> We can reproduce this BUG() in the current Linus tree with DAX PMDs.
> Andrew, can you send this patch to Linus for inclusion in 4.7?

Wilco, thanks.