re: sched, numa, mm: Implement constant, per task Working Set Sampling (WSS) rate

[Peter Zijlstra]

On Mon, 2012-10-22 at 14:55 +0300, Dan Carpenter wrote:
> Hello Peter Zijlstra,
> 
> The patch 3d049f8a5398: "sched, numa, mm: Implement constant, per
> task Working Set Sampling (WSS) rate" from Oct 14, 2012, leads to the
> following warning:
> kernel/sched/fair.c:954 task_numa_work()
>error: we previously assumed 'vma' could be null (see line 948)
> 
>943  if (!vma) {
>944  ACCESS_ONCE(mm->numa_scan_seq)++;
>945  offset = 0;
>946  vma = mm->mmap;
>947  }
>948  while (vma && !vma_migratable(vma)) {
>^^^
> If this is NULL,
>949  vma = vma->vm_next;
>950  if (!vma)
>951  goto again;
>952  }
>953  
>954  offset = max(offset, vma->vm_start);
>  ^
> then it leads to a NULL dereference here.

Ah.. indeed so. There's also what looks like an infinite loop in there
if nothing is migratable or if length is stupid large. The below should
avoid the reported NULL deref as well as break out when we've reached
the end of the address space.


---
 kernel/sched/fair.c |   23 ---
 1 files changed, 8 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c68b877..5a6d8f5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -939,29 +939,22 @@ void task_numa_work(struct callback_head *work)
 
down_read(>mmap_sem);
vma = find_vma(mm, offset);
-again:
if (!vma) {
ACCESS_ONCE(mm->numa_scan_seq)++;
offset = 0;
vma = mm->mmap;
}
-   while (vma && !vma_migratable(vma)) {
-   vma = vma->vm_next;
-   if (!vma)
-   goto again;
-   }
-
-   offset = max(offset, vma->vm_start);
-   end = min(ALIGN(offset + length, HPAGE_SIZE), vma->vm_end);
-   length -= end - offset;
+   for (; vma && length > 0; vma = vma->vm_next) {
+   if (!vma_migratable(vma))
+   continue;
 
-   change_prot_none(vma, offset, end);
+   offset = max(offset, vma->vm_start);
+   end = min(ALIGN(offset + length, HPAGE_SIZE), vma->vm_end);
+   length -= end - offset;
 
-   offset = end;
+   change_prot_none(vma, offset, end);
 
-   if (length > 0) {
-   vma = vma->vm_next;
-   goto again;
+   offset = end;
}
mm->numa_scan_offset = offset;
up_read(>mmap_sem);

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re: sched, numa, mm: Implement constant, per task Working Set Sampling (WSS) rate

[Dan Carpenter]

Hello Peter Zijlstra,

The patch 3d049f8a5398: "sched, numa, mm: Implement constant, per
task Working Set Sampling (WSS) rate" from Oct 14, 2012, leads to the
following warning:
kernel/sched/fair.c:954 task_numa_work()
 error: we previously assumed 'vma' could be null (see line 948)

   943  if (!vma) {
   944  ACCESS_ONCE(mm->numa_scan_seq)++;
   945  offset = 0;
   946  vma = mm->mmap;
   947  }
   948  while (vma && !vma_migratable(vma)) {
   ^^^
If this is NULL,
   949  vma = vma->vm_next;
   950  if (!vma)
   951  goto again;
   952  }
   953  
   954  offset = max(offset, vma->vm_start);
 ^
then it leads to a NULL dereference here.

regards,
dan carpenter

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re: sched, numa, mm: Implement constant, per task Working Set Sampling (WSS) rate

[Dan Carpenter]

Hello Peter Zijlstra,

The patch 3d049f8a5398: sched, numa, mm: Implement constant, per
task Working Set Sampling (WSS) rate from Oct 14, 2012, leads to the
following warning:
kernel/sched/fair.c:954 task_numa_work()
 error: we previously assumed 'vma' could be null (see line 948)

   943  if (!vma) {
   944  ACCESS_ONCE(mm-numa_scan_seq)++;
   945  offset = 0;
   946  vma = mm-mmap;
   947  }
   948  while (vma  !vma_migratable(vma)) {
   ^^^
If this is NULL,
   949  vma = vma-vm_next;
   950  if (!vma)
   951  goto again;
   952  }
   953  
   954  offset = max(offset, vma-vm_start);
 ^
then it leads to a NULL dereference here.

regards,
dan carpenter

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re: sched, numa, mm: Implement constant, per task Working Set Sampling (WSS) rate

[Peter Zijlstra]

On Mon, 2012-10-22 at 14:55 +0300, Dan Carpenter wrote:
 Hello Peter Zijlstra,
 
 The patch 3d049f8a5398: sched, numa, mm: Implement constant, per
 task Working Set Sampling (WSS) rate from Oct 14, 2012, leads to the
 following warning:
 kernel/sched/fair.c:954 task_numa_work()
error: we previously assumed 'vma' could be null (see line 948)
 
943  if (!vma) {
944  ACCESS_ONCE(mm-numa_scan_seq)++;
945  offset = 0;
946  vma = mm-mmap;
947  }
948  while (vma  !vma_migratable(vma)) {
^^^
 If this is NULL,
949  vma = vma-vm_next;
950  if (!vma)
951  goto again;
952  }
953  
954  offset = max(offset, vma-vm_start);
  ^
 then it leads to a NULL dereference here.

Ah.. indeed so. There's also what looks like an infinite loop in there
if nothing is migratable or if length is stupid large. The below should
avoid the reported NULL deref as well as break out when we've reached
the end of the address space.


---
 kernel/sched/fair.c |   23 ---
 1 files changed, 8 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c68b877..5a6d8f5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -939,29 +939,22 @@ void task_numa_work(struct callback_head *work)
 
down_read(mm-mmap_sem);
vma = find_vma(mm, offset);
-again:
if (!vma) {
ACCESS_ONCE(mm-numa_scan_seq)++;
offset = 0;
vma = mm-mmap;
}
-   while (vma  !vma_migratable(vma)) {
-   vma = vma-vm_next;
-   if (!vma)
-   goto again;
-   }
-
-   offset = max(offset, vma-vm_start);
-   end = min(ALIGN(offset + length, HPAGE_SIZE), vma-vm_end);
-   length -= end - offset;
+   for (; vma  length  0; vma = vma-vm_next) {
+   if (!vma_migratable(vma))
+   continue;
 
-   change_prot_none(vma, offset, end);
+   offset = max(offset, vma-vm_start);
+   end = min(ALIGN(offset + length, HPAGE_SIZE), vma-vm_end);
+   length -= end - offset;
 
-   offset = end;
+   change_prot_none(vma, offset, end);
 
-   if (length  0) {
-   vma = vma-vm_next;
-   goto again;
+   offset = end;
}
mm-numa_scan_offset = offset;
up_read(mm-mmap_sem);

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