linux-kernel - Re: BUG: unable to handle kernel paging request at ffffe8ff7fc00001

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Message-ID: <CA+55aFzTTUYqSWRsiX_XnouKQbXMweLS0JFeyEXe72dWA--1Rw@mail.gmail.com>
Date:	Sun, 15 Nov 2015 16:59:57 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Kyle Sanderson <kyle.leet@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linux-Kernal <linux-kernel@...r.kernel.org>
Subject: Re: BUG: unable to handle kernel paging request at ffffe8ff7fc00001

On Sun, Nov 15, 2015 at 2:28 PM, Kyle Sanderson <kyle.leet@...il.com> wrote:
> [] BUG: unable to handle kernel paging request at ffffe8ff7fc00001
> [] IP: [<ffffffff810a174f>] kstat_irqs+0x4f/0x90
> [] CPU: 2 PID: 1078 Comm: usage.pl Not tainted 4.1.7-hardened-r1 #1
> [] Hardware name: Supermicro Super Server/X10SRi-F, BIOS 1.0b 04/21/2015
RSI: 000060f700000001
> [] Call Trace:
> []  [<>] kstat_irqs_usr+0x1e/0x40
> []  [<>] show_stat+0x5ca/0x690
> []  [<>] seq_read+0xcd/0x3b0
> []  [<>] proc_reg_read+0x43/0x70
> []  [<>] __vfs_read+0x23/0xd0
> []  [<>] vfs_read+0xc0/0x1d0
> []  [<>] SyS_read+0x41/0xb0
> []  [<>] system_call_fastpath+0x16/0x72
> [] Code: 83 78 48 00 74 56 4c 8b ...

The code ends up being

  mov    0x48(%r13),%rsi
  mov    __per_cpu_offset(,%rcx,8),%rcx
  add    (%rsi,%rcx,1),%ebx <-- trapping instruction

which is just the

   sum += *per_cpu_ptr(desc->kstat_irqs, cpu);

part of kstat_irqs().

Your registers being

   RSI: 000060f700000001
   RCX: ffff88087fc00000

and it's RSI that makes no sense - RCX looks like a real kernel
pointer. So it looks like it's the "desc->kstat_irqs" thing that is
for some reason garbage.

I don't see any sane possible reason this would happen, though.
Thomas, does this look like anything you've seen before?

                 Linus
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