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    SubjectRe: BUG: unable to handle kernel paging request
    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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