Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > linux.kernel > #1320811 > unrolled thread
| Started by | Andrea Arcangeli <aarcange@redhat.com> |
|---|---|
| First post | 2016-01-28 16:50 +0100 |
| Last post | 2016-01-29 11:40 +0100 |
| Articles | 2 — 2 participants |
Back to article view | Back to linux.kernel
This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by
below is the oldest one visible, not the original post.
Re: mm: BUG in expand_downwards Andrea Arcangeli <aarcange@redhat.com> - 2016-01-28 16:50 +0100
Re: mm: BUG in expand_downwards Dmitry Vyukov <dvyukov@google.com> - 2016-01-29 11:40 +0100
| From | Andrea Arcangeli <aarcange@redhat.com> |
|---|---|
| Date | 2016-01-28 16:50 +0100 |
| Subject | Re: mm: BUG in expand_downwards |
| Message-ID | <qVWZB-5wF-45@gated-at.bofh.it> |
Hello,
On Wed, Jan 27, 2016 at 10:11:44PM +0100, Dmitry Vyukov wrote:
> Sorry, I meant only the second once. The mm bug.
> I guess you need at least CONFIG_DEBUG_VM. Run it in a tight parallel
> loop with CPU oversubscription (e.g. 32 parallel processes on 2 cores)
> for at least an hour.
Does this help for the mm bug?
From 0cc410ae59800444ca929e3dc48e4f1580a95be6 Mon Sep 17 00:00:00 2001
From: Andrea Arcangeli <aarcange@redhat.com>
Date: Thu, 28 Jan 2016 16:34:44 +0100
Subject: [PATCH 1/1] mm: validate_mm browse_rb SMP race condition
The mmap_sem for reading in validate_mm called from expand_stack is
not enough to prevent the argumented rbtree rb_subtree_gap information
to change from under us because expand_stack may be running from other
threads concurrently which will hold the mmap_sem for reading too.
The argumented rbtree is updated with vma_gap_update under the
page_table_lock so use it in browse_rb() too to avoid false positives.
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
mm/mmap.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index f384def..8389e03 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -389,8 +389,9 @@ static long vma_compute_subtree_gap(struct vm_area_struct *vma)
}
#ifdef CONFIG_DEBUG_VM_RB
-static int browse_rb(struct rb_root *root)
+static int browse_rb(struct mm_struct *mm)
{
+ struct rb_root *root = &mm->mm_rb;
int i = 0, j, bug = 0;
struct rb_node *nd, *pn = NULL;
unsigned long prev = 0, pend = 0;
@@ -413,12 +414,14 @@ static int browse_rb(struct rb_root *root)
vma->vm_start, vma->vm_end);
bug = 1;
}
+ spin_lock(&mm->page_table_lock);
if (vma->rb_subtree_gap != vma_compute_subtree_gap(vma)) {
pr_emerg("free gap %lx, correct %lx\n",
vma->rb_subtree_gap,
vma_compute_subtree_gap(vma));
bug = 1;
}
+ spin_unlock(&mm->page_table_lock);
i++;
pn = nd;
prev = vma->vm_start;
@@ -474,7 +477,7 @@ static void validate_mm(struct mm_struct *mm)
mm->highest_vm_end, highest_address);
bug = 1;
}
- i = browse_rb(&mm->mm_rb);
+ i = browse_rb(mm);
if (i != mm->map_count) {
if (i != -1)
pr_emerg("map_count %d rb %d\n", mm->map_count, i);
[toc] | [next] | [standalone]
| From | Dmitry Vyukov <dvyukov@google.com> |
|---|---|
| Date | 2016-01-29 11:40 +0100 |
| Message-ID | <qWeD8-1qJ-23@gated-at.bofh.it> |
| In reply to | #1320811 |
On Thu, Jan 28, 2016 at 4:47 PM, Andrea Arcangeli <aarcange@redhat.com> wrote:
> Hello,
>
> On Wed, Jan 27, 2016 at 10:11:44PM +0100, Dmitry Vyukov wrote:
>> Sorry, I meant only the second once. The mm bug.
>> I guess you need at least CONFIG_DEBUG_VM. Run it in a tight parallel
>> loop with CPU oversubscription (e.g. 32 parallel processes on 2 cores)
>> for at least an hour.
>
> Does this help for the mm bug?
Yes, it seems to fix the issue.
I will also run fuzzer with this patch and report if I see it again.
> From 0cc410ae59800444ca929e3dc48e4f1580a95be6 Mon Sep 17 00:00:00 2001
> From: Andrea Arcangeli <aarcange@redhat.com>
> Date: Thu, 28 Jan 2016 16:34:44 +0100
> Subject: [PATCH 1/1] mm: validate_mm browse_rb SMP race condition
>
> The mmap_sem for reading in validate_mm called from expand_stack is
> not enough to prevent the argumented rbtree rb_subtree_gap information
> to change from under us because expand_stack may be running from other
> threads concurrently which will hold the mmap_sem for reading too.
>
> The argumented rbtree is updated with vma_gap_update under the
> page_table_lock so use it in browse_rb() too to avoid false positives.
>
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
> ---
> mm/mmap.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index f384def..8389e03 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -389,8 +389,9 @@ static long vma_compute_subtree_gap(struct vm_area_struct *vma)
> }
>
> #ifdef CONFIG_DEBUG_VM_RB
> -static int browse_rb(struct rb_root *root)
> +static int browse_rb(struct mm_struct *mm)
> {
> + struct rb_root *root = &mm->mm_rb;
> int i = 0, j, bug = 0;
> struct rb_node *nd, *pn = NULL;
> unsigned long prev = 0, pend = 0;
> @@ -413,12 +414,14 @@ static int browse_rb(struct rb_root *root)
> vma->vm_start, vma->vm_end);
> bug = 1;
> }
> + spin_lock(&mm->page_table_lock);
> if (vma->rb_subtree_gap != vma_compute_subtree_gap(vma)) {
> pr_emerg("free gap %lx, correct %lx\n",
> vma->rb_subtree_gap,
> vma_compute_subtree_gap(vma));
> bug = 1;
> }
> + spin_unlock(&mm->page_table_lock);
> i++;
> pn = nd;
> prev = vma->vm_start;
> @@ -474,7 +477,7 @@ static void validate_mm(struct mm_struct *mm)
> mm->highest_vm_end, highest_address);
> bug = 1;
> }
> - i = browse_rb(&mm->mm_rb);
> + i = browse_rb(mm);
> if (i != mm->map_count) {
> if (i != -1)
> pr_emerg("map_count %d rb %d\n", mm->map_count, i);
[toc] | [prev] | [standalone]
Back to top | Article view | linux.kernel
csiph-web