linux-kernel - [PATCH] thp: Fix deadlock situation in vma

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Date:	Fri, 9 Aug 2013 14:34:35 -0700
From:	Ning Qu <quning@...gle.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Matthew Wilcox <willy@...ux.intel.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	linux-fsdevel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Dave Hansen <dave@...1.net>, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Ning Qu <quning@...gle.com>
Subject: [PATCH] thp: Fix deadlock situation in vma_adjust with huge page in
 page cache.

In vma_adjust, the current code grabs i_mmap_mutex before calling
vma_adjust_trans_huge. This used to be fine until huge page in page
cache comes in. The problem is the underlying function
split_file_huge_page will also grab the i_mmap_mutex before splitting
the huge page in page cache. Obviously this is causing deadlock
situation.

This fix is to move the vma_adjust_trans_huge before grab the lock for
file, the same as what the function is currently doing for anonymous
memory. Tested, everything works fine so far.

Signed-off-by: Ning Qu <quning@...gle.com>
---
 mm/mmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 519ce78..accf1b3 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -750,6 +750,8 @@ again: remove_next = 1 + (end > next->vm_end);
  }
  }

+ vma_adjust_trans_huge(vma, start, end, adjust_next);
+
  if (file) {
  mapping = file->f_mapping;
  if (!(vma->vm_flags & VM_NONLINEAR)) {
@@ -773,8 +775,6 @@ again: remove_next = 1 + (end > next->vm_end);
  }
  }

- vma_adjust_trans_huge(vma, start, end, adjust_next);
-
  anon_vma = vma->anon_vma;
  if (!anon_vma && adjust_next)
  anon_vma = next->anon_vma;
-- 
1.8.3
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