[PATCH] fs/proc/task_mmu.c: assume non-NULL vma in pagemap_hugetlb() (Re: [mmotm:master 97/220] fs/proc/task_mmu.c:1042 pagemap_hugetlb() error: we previously assumed 'vma' could be null (see line 1037))

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

Hi Fengguang,

On Fri, Feb 14, 2014 at 09:04:50PM +0800, Fengguang Wu wrote:
...
> FYI, there are new smatch warnings show up in
> 
> tree:   git://git.cmpxchg.org/linux-mmotm.git master
> head:   0363f94bc1c9b81f23ee7d2446331eb288568ea7
> commit: 81272031cc2831a3d1abb3c681f1188aa36a1454 [97/220] pagewalk: remove argument hmask from hugetlb_entry()
> 
> fs/proc/task_mmu.c:1042 pagemap_hugetlb() error: we previously assumed 'vma' could be null (see line 1037)
> 
> vim +/vma +1042 fs/proc/task_mmu.c
> 
> d9104d1c Cyrill Gorcunov       2013-09-11  1031  	int flags2;
> 16fbdce6 Konstantin Khlebnikov 2012-05-10  1032  	pagemap_entry_t pme;
> 81272031 Naoya Horiguchi       2014-02-13  1033  	unsigned long hmask;
> 5dc37642 Naoya Horiguchi       2009-12-14  1034  
> d9104d1c Cyrill Gorcunov       2013-09-11  1035  	WARN_ON_ONCE(!vma);
> d9104d1c Cyrill Gorcunov       2013-09-11  1036  
> d9104d1c Cyrill Gorcunov       2013-09-11 @1037  	if (vma && (vma->vm_flags & VM_SOFTDIRTY))
> d9104d1c Cyrill Gorcunov       2013-09-11  1038  		flags2 = __PM_SOFT_DIRTY;
> d9104d1c Cyrill Gorcunov       2013-09-11  1039  	else
> d9104d1c Cyrill Gorcunov       2013-09-11  1040  		flags2 = 0;
> d9104d1c Cyrill Gorcunov       2013-09-11  1041  
> 21a2f342 Naoya Horiguchi       2014-02-13 @1042  	hmask = huge_page_mask(hstate_vma(vma));
> 5dc37642 Naoya Horiguchi       2009-12-14  1043  	for (; addr != end; addr += PAGE_SIZE) {
> 116354d1 Naoya Horiguchi       2010-04-06  1044  		int offset = (addr & ~hmask) >> PAGE_SHIFT;
> d9104d1c Cyrill Gorcunov       2013-09-11  1045  		huge_pte_to_pagemap_entry(&pme, pm, *pte, offset, flags2);

Thanks for reporting, here is a patch.
We never have NULL vma in pagemap_hugetlb(), I added the BUG_ON check.

Thanks,
Naoya Horiguchi
---
From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Date: Fri, 14 Feb 2014 09:35:06 -0500
Subject: [PATCH] fs/proc/task_mmu.c: assume non-NULL vma in pagemap_hugetlb()

Fengguang reported smatch error about potential NULL pointer access.

In updated page table walker, we never run ->hugetlb_entry() callback
on the address without vma. This is because __walk_page_range() checks
it in advance. So we can assume non-NULL vma in pagemap_hugetlb().

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
---
 fs/proc/task_mmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index f819d0d4a0e8..69aed7192254 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1032,9 +1032,9 @@ static int pagemap_hugetlb(pte_t *pte, unsigned long addr, unsigned long end,
 	pagemap_entry_t pme;
 	unsigned long hmask;
 
-	WARN_ON_ONCE(!vma);
+	BUG_ON(!vma);
 
-	if (vma && (vma->vm_flags & VM_SOFTDIRTY))
+	if (vma->vm_flags & VM_SOFTDIRTY)
 		flags2 = __PM_SOFT_DIRTY;
 	else
 		flags2 = 0;
-- 
1.8.5.3

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