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

[Matthew Wilcox]

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@xxxxxxxxxxxxxxx>