linux-kernel - Re: BUG: unable to handle kernel paging request

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Date:	Sun, 27 Mar 2011 08:37:24 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Anca Emanuel <anca.emanuel@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: BUG: unable to handle kernel paging request

Al, this smells like your /proc cleanups/fixes...

On Sun, Mar 27, 2011 at 2:16 AM, Anca Emanuel <anca.emanuel@...il.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.

> [15117.080660] Call Trace:
> [15117.080671]  [<ffffffff811b4a3a>] m_stop+0x1a/0x40
> [15117.080685]  [<ffffffff8117d991>] seq_read+0x1e1/0x420
> [15117.080698]  [<ffffffff8115c685>] vfs_read+0xc5/0x190
> [15117.080711]  [<ffffffff8115c851>] sys_read+0x51/0x90
> [15117.080724]  [<ffffffff815b2d02>] system_call_fastpath+0x16/0x1b

Al?

                               Linus
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