Re: [PATCH] mm: Fix potential NULL pointer dereference

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

On Wed, Jul 24, 2013 at 12:22:08PM +0800, Wanpeng Li wrote:
>On Wed, Jul 24, 2013 at 11:48:19AM +0800, Libin wrote:
>>find_vma may return NULL, thus check the return
>>value to avoid NULL pointer dereference.
>>
>
>When can this happen since down_read(&mm->mmap_sem) is held?
>

Between mmap_sem read lock released and write lock held I think.

>>Signed-off-by: Libin <huawei.libin@huawei.com>
>>---
>> mm/huge_memory.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>>diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>index 243e710..d4423f4 100644
>>--- a/mm/huge_memory.c
>>+++ b/mm/huge_memory.c
>>@@ -2294,6 +2294,8 @@ static void collapse_huge_page(struct mm_struct *mm,
>> 		goto out;
>>
>> 	vma = find_vma(mm, address);
>>+	if (!vma)
>>+		goto out;
>> 	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
>> 	hend = vma->vm_end & HPAGE_PMD_MASK;
>> 	if (address < hstart || address + HPAGE_PMD_SIZE > hend)
>>-- 
>>1.8.2.1
>>
>>
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