releases/3.6.8/xen-events-fix-rcu-warning-or-call-idle-notifier-after-irq_enter.patch

   1 From 772aebcefeff310f80e32b874988af0076cb799d Mon Sep 17 00:00:00 2001
   2 From: Mojiong Qiu <qiumojiong@gmail.com>
   3 Date: Tue, 6 Nov 2012 16:08:15 +0800
   4 Subject: xen/events: fix RCU warning, or Call idle notifier after irq_enter()
   5
   6 From: Mojiong Qiu <qiumojiong@gmail.com>
   7
   8 commit 772aebcefeff310f80e32b874988af0076cb799d upstream.
   9
  10 exit_idle() should be called after irq_enter(), otherwise it throws:
  11
  12 [ INFO: suspicious RCU usage. ]
  13 3.6.5 #1 Not tainted
  14 -------------------------------
  15 include/linux/rcupdate.h:725 rcu_read_lock() used illegally while idle!
  16
  17 other info that might help us debug this:
  18
  19 RCU used illegally from idle CPU!
  20 rcu_scheduler_active = 1, debug_locks = 1
  21 RCU used illegally from extended quiescent state!
  22 1 lock held by swapper/0/0:
  23  #0:  (rcu_read_lock){......}, at: [<ffffffff810e9fe0>] __atomic_notifier_call_chain+0x0/0x140
  24
  25 stack backtrace:
  26 Pid: 0, comm: swapper/0 Not tainted 3.6.5 #1
  27 Call Trace:
  28  <IRQ>  [<ffffffff811259a2>] lockdep_rcu_suspicious+0xe2/0x130
  29  [<ffffffff810ea10c>] __atomic_notifier_call_chain+0x12c/0x140
  30  [<ffffffff810e9fe0>] ? atomic_notifier_chain_unregister+0x90/0x90
  31  [<ffffffff811216cd>] ? trace_hardirqs_off+0xd/0x10
  32  [<ffffffff810ea136>] atomic_notifier_call_chain+0x16/0x20
  33  [<ffffffff810777c3>] exit_idle+0x43/0x50
  34  [<ffffffff81568865>] xen_evtchn_do_upcall+0x25/0x50
  35  [<ffffffff81aa690e>] xen_do_hypervisor_callback+0x1e/0x30
  36  <EOI>  [<ffffffff810013aa>] ? hypercall_page+0x3aa/0x1000
  37  [<ffffffff810013aa>] ? hypercall_page+0x3aa/0x1000
  38  [<ffffffff81061540>] ? xen_safe_halt+0x10/0x20
  39  [<ffffffff81075cfa>] ? default_idle+0xba/0x570
  40  [<ffffffff810778af>] ? cpu_idle+0xdf/0x140
  41  [<ffffffff81a4d881>] ? rest_init+0x135/0x144
  42  [<ffffffff81a4d74c>] ? csum_partial_copy_generic+0x16c/0x16c
  43  [<ffffffff82520c45>] ? start_kernel+0x3db/0x3e8
  44  [<ffffffff8252066a>] ? repair_env_string+0x5a/0x5a
  45  [<ffffffff82520356>] ? x86_64_start_reservations+0x131/0x135
  46  [<ffffffff82524aca>] ? xen_start_kernel+0x465/0x46
  47
  48 Git commit 98ad1cc14a5c4fd658f9d72c6ba5c86dfd3ce0d5
  49 Author: Frederic Weisbecker <fweisbec@gmail.com>
  50 Date:   Fri Oct 7 18:22:09 2011 +0200
  51
  52     x86: Call idle notifier after irq_enter()
  53
  54 did this, but it missed the Xen code.
  55
  56 Signed-off-by: Mojiong Qiu <mjqiu@tencent.com>
  57 Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
  58 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  59
  60 ---
  61  drivers/xen/events.c |    2 +-
  62  1 file changed, 1 insertion(+), 1 deletion(-)
  63
  64 --- a/drivers/xen/events.c
  65 +++ b/drivers/xen/events.c
  66 @@ -1374,8 +1374,8 @@ void xen_evtchn_do_upcall(struct pt_regs
  67  {
  68         struct pt_regs *old_regs = set_irq_regs(regs);
  69
  70 -       exit_idle();
  71         irq_enter();
  72 +       exit_idle();
  73
  74         __xen_evtchn_do_upcall();
  75