Re: BUG: unable to handle kernel paging request

["Américo Wang" <xiyou.wangcong@gmail.com>]

On Sun, Mar 27, 2011 at 11:37 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> Al, this smells like your /proc cleanups/fixes...
>
> On Sun, Mar 27, 2011 at 2:16 AM, Anca Emanuel <anca.emanuel@gmail.com> wrote:
>> Hi, I'm using latest kernel git.
>>
>>
>> [15117.080119] BUG: unable to handle kernel paging request at fffffffffffffff3
>
> That's "-13" (possibly -EACCES)
>
>> [15117.080152] IP: [<ffffffff811b4989>] vma_stop+0x19/0x40
>
> .. and the code disassembles to
>
>   0:   55                      push   %rbp
>   1:   48 89 e5                mov    %rsp,%rbp
>   4:   53                      push   %rbx
>   5:   48 83 ec 08             sub    $0x8,%rsp
>   9:   0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
>   e:   48 85 f6                test   %rsi,%rsi
>  11:   74 1a                   je     0x2d
>  13:   48 39 77 10             cmp    %rsi,0x10(%rdi)
>  17:   74 14                   je     0x2d
>  19:   8b 1e                   mov    (%rsi),%ebx
>  1b:   48 8d 7b 60             lea    0x60(%rbx),%rdi
>  1f:   e8 eb 2f ed ff          callq  up_read
>
> where that instruction at 0x19 is the access "mm = vma->vm_mm". So
> it's vma that is -EPERM.
>
> I bet it's due to commit ec6fd8a4355c ("report errors in /proc/*/*map*
> sanely"), which replaces NULL with various ERR_PTR() cases.
>

Exactly... should be fixed by something like:

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 7c708a4..6b82632 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -90,7 +90,7 @@ static void pad_len_spaces(struct seq_file *m, int len)

 static void vma_stop(struct proc_maps_private *priv, struct
vm_area_struct *vma)
 {
-       if (vma && vma != priv->tail_vma) {
+       if (vma && !IS_ERR(vma) && vma != priv->tail_vma) {
                struct mm_struct *mm = vma->vm_mm;
                up_read(&mm->mmap_sem);
                mmput(mm);