linux-kernel - Re: [PATCH 09/10] huge pagecache: mmap_sem is unlocked when truncation splits pmd

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Message-ID: <20160414173922.GE3120@linux.intel.com>
Date:	Thu, 14 Apr 2016 13:39:22 -0400
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Yang Shi <yang.shi@...aro.org>, Ning Qu <quning@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 09/10] huge pagecache: mmap_sem is unlocked when
 truncation splits pmd

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?

Tested-by: Matthew Wilcox <willy@...ux.intel.com>