linux-kernel - [PATCH 3.15 35/37] mm: do not call do_fault

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Message-Id: <20140730014829.452894556@linuxfoundation.org>
Date:	Tue, 29 Jul 2014 18:49:11 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Konstantin Khlebnikov <koct9i@...il.com>,
	Ingo Korb <ingo.korb@...dortmund.de>,
	Hugh Dickins <hughd@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Dave Jones <davej@...hat.com>, Ning Qu <quning@...gle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 3.15 35/37] mm: do not call do_fault_around for non-linear fault

3.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Konstantin Khlebnikov <koct9i@...il.com>

commit c118678bc79e8241f9d3434d9324c6400d72f48a upstream.

Ingo Korb reported that "repeated mapping of the same file on tmpfs
using remap_file_pages sometimes triggers a BUG at mm/filemap.c:202 when
the process exits".

He bisected the bug to d7c1755179b8 ("mm: implement ->map_pages for
shmem/tmpfs"), although the bug was actually added by commit
8c6e50b0290c ("mm: introduce vm_ops->map_pages()").

The problem is caused by calling do_fault_around for a _non-linear_
fault.  In this case pgoff is shifted and might become negative during
calculation.

Faulting around non-linear page-fault makes no sense and breaks the
logic in do_fault_around because pgoff is shifted.

Signed-off-by: Konstantin Khlebnikov <koct9i@...il.com>
Reported-by: Ingo Korb <ingo.korb@...dortmund.de>
Tested-by: Ingo Korb <ingo.korb@...dortmund.de>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Sasha Levin <sasha.levin@...cle.com>
Cc: Dave Jones <davej@...hat.com>
Cc: Ning Qu <quning@...gle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/memory.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3515,7 +3515,7 @@ static int do_read_fault(struct mm_struc
 	 * if page by the offset is not ready to be mapped (cold cache or
 	 * something).
 	 */
-	if (vma->vm_ops->map_pages) {
+	if (vma->vm_ops->map_pages && !(flags & FAULT_FLAG_NONLINEAR)) {
 		pte = pte_offset_map_lock(mm, pmd, address, &ptl);
 		do_fault_around(vma, address, pte, pgoff, flags);
 		if (!pte_same(*pte, orig_pte))

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