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Date: Fri, 29 Jan 2010 16:57:31 -0800
Message-ID: <6cafb0f01001291657q4ccbee86rce3143a4be7a1433@mail.gmail.com>
Subject: Bug in find_vma_prev - mmap.c
From: Tony Perkins <da.perk@gmail.com>
To: linux-kernel@vger.kernel.org
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This code returns vma (mm->mmap) if it sees that addr is lower than first VMA.
However, I think it falsely returns vma (mm->mmap) on the case where
addr is in the first VMA.

If it is the first VMA region:
- *pprev should be set to NULL
- implying prev is NULL
- and should therefore return vma (so in this case, I just added if
it's the first VMA and it's within range)

/* Same as find_vma, but also return a pointer to the previous VMA in *pprev. */
struct vm_area_struct *
find_vma_prev(struct mm_struct *mm, unsigned long addr,
??? ??? ??? struct vm_area_struct **pprev)
{
??? struct vm_area_struct *vma = NULL, *prev = NULL;
??? struct rb_node *rb_node;
??? if (!mm)
??? ??? goto out;

??? /* Guard against addr being lower than the first VMA */
??? vma = mm->mmap;

??? /* Go through the RB tree quickly. */
??? rb_node = mm->mm_rb.rb_node;

??? while (rb_node) {
??? ??? struct vm_area_struct *vma_tmp;
??? ??? vma_tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);

??? ??? if (addr < vma_tmp->vm_end) {
??????????? // TONY: if (vma_tmp->vm_start <= addr) vma = vma_tmp; //
this returns the correct 'vma' when vma is the first node (i.e., no
prev)
??? ??? ??? rb_node = rb_node->rb_left;
??? ??? } else {
??? ??? ??? prev = vma_tmp;
??? ??? ??? if (!prev->vm_next || (addr < prev->vm_next->vm_end))
??? ??? ??? ??? break;
??? ??? ??? rb_node = rb_node->rb_right;
??? ??? }
??? }

out:
??? *pprev = prev;
??? return prev ? prev->vm_next : vma;
}

Is this a known issue and/or has this problem been addressed?
Also, please CC my email address with responses.

Thanks,
--tony

--
Aim for Perfection!
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