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Date: Sun, 27 Mar 2011 13:52:03 -0400
From: Stephen Wilson <wilsons@start.ca>
To: =?utf-8?Q?Am=C3=A9rico?= Wang <xiyou.wangcong@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Anca Emanuel <anca.emanuel@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>, "Luck, Tony" <tony.luck@intel.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: BUG: unable to handle kernel paging request
Message-ID: <20110327175203.GA15862@fibrous.localdomain>
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On Mon, Mar 28, 2011 at 12:00:44AM +0800, Américo Wang wrote:
> 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);

FWIW, that looks like the right fix to me.

Also CC'ing Tony Luck as he reported what appears to be the same issue
on the 25'th.

-- 
steve

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