timers: handle HRTIMER_CB_IRQSAFE_UNLOCKED correctly from softirq context
authorGautham R Shenoy <ego@in.ibm.com>
Sat, 25 Oct 2008 04:52:38 +0000 (09:52 +0530)
committerThomas Gleixner <tglx@linutronix.de>
Tue, 11 Nov 2008 09:46:42 +0000 (10:46 +0100)
commit5d5254f0d3b9bebc47d97e357374c0ad0c291a7d
treefea216db5914228fe80139f5e31621de86cc9e5d
parentae99286b4f1be7788f2d6947c66a91dbd6351eec
timers: handle HRTIMER_CB_IRQSAFE_UNLOCKED correctly from softirq context

Impact: fix incorrect locking triggered during hotplug-intense stress-tests

While migrating the the CB_IRQSAFE_UNLOCKED timers during a cpu-offline,
we queue them on the cb_pending list, so that they won't go
stale.

Thus, when the callbacks of the timers run from the softirq context,
they could run into potential deadlocks, since these callbacks
assume that they're running with irq's disabled, thereby annoying
lockdep!

Fix this by emulating hardirq context while running these callbacks from
the hrtimer softirq.

=================================
[ INFO: inconsistent lock state ]
2.6.27 #2
--------------------------------
inconsistent {in-hardirq-W} -> {hardirq-on-W} usage.
ksoftirqd/0/4 [HC0[0]:SC1[1]:HE1:SE0] takes:
 (&rq->lock){++..}, at: [<c011db84>] sched_rt_period_timer+0x9e/0x1fc
{in-hardirq-W} state was registered at:
  [<c014103c>] __lock_acquire+0x549/0x121e
  [<c0107890>] native_sched_clock+0x88/0x99
  [<c013aa12>] clocksource_get_next+0x39/0x3f
  [<c0139abc>] update_wall_time+0x616/0x7df
  [<c0141d6b>] lock_acquire+0x5a/0x74
  [<c0121724>] scheduler_tick+0x3a/0x18d
  [<c047ed45>] _spin_lock+0x1c/0x45
  [<c0121724>] scheduler_tick+0x3a/0x18d
  [<c0121724>] scheduler_tick+0x3a/0x18d
  [<c012c436>] update_process_times+0x3a/0x44
  [<c013c044>] tick_periodic+0x63/0x6d
  [<c013c062>] tick_handle_periodic+0x14/0x5e
  [<c010568c>] timer_interrupt+0x44/0x4a
  [<c0150c9f>] handle_IRQ_event+0x13/0x3d
  [<c0151c14>] handle_level_irq+0x79/0xbd
  [<c0105634>] do_IRQ+0x69/0x7d
  [<c01041e4>] common_interrupt+0x28/0x30
  [<c047007b>] aac_probe_one+0x1a3/0x3f3
  [<c047ec2d>] _spin_unlock_irqrestore+0x36/0x39
  [<c01512b4>] setup_irq+0x1be/0x1f9
  [<c065d70b>] start_kernel+0x259/0x2c5
  [<ffffffff>] 0xffffffff
irq event stamp: 50102
hardirqs last  enabled at (50102): [<c047ebf4>] _spin_unlock_irq+0x20/0x23
hardirqs last disabled at (50101): [<c047edc2>] _spin_lock_irq+0xa/0x4b
softirqs last  enabled at (50088): [<c0128ba6>] do_softirq+0x37/0x4d
softirqs last disabled at (50099): [<c0128ba6>] do_softirq+0x37/0x4d

other info that might help us debug this:
no locks held by ksoftirqd/0/4.

stack backtrace:
Pid: 4, comm: ksoftirqd/0 Not tainted 2.6.27 #2
 [<c013f6cb>] print_usage_bug+0x13e/0x147
 [<c013fef5>] mark_lock+0x493/0x797
 [<c01410b1>] __lock_acquire+0x5be/0x121e
 [<c0141d6b>] lock_acquire+0x5a/0x74
 [<c011db84>] sched_rt_period_timer+0x9e/0x1fc
 [<c047ed45>] _spin_lock+0x1c/0x45
 [<c011db84>] sched_rt_period_timer+0x9e/0x1fc
 [<c011db84>] sched_rt_period_timer+0x9e/0x1fc
 [<c01210fd>] finish_task_switch+0x41/0xbd
 [<c0107890>] native_sched_clock+0x88/0x99
 [<c011dae6>] sched_rt_period_timer+0x0/0x1fc
 [<c0136dda>] run_hrtimer_pending+0x54/0xe5
 [<c011dae6>] sched_rt_period_timer+0x0/0x1fc
 [<c0128afb>] __do_softirq+0x7b/0xef
 [<c0128ba6>] do_softirq+0x37/0x4d
 [<c0128c12>] ksoftirqd+0x56/0xc5
 [<c0128bbc>] ksoftirqd+0x0/0xc5
 [<c0134649>] kthread+0x38/0x5d
 [<c0134611>] kthread+0x0/0x5d
 [<c0104477>] kernel_thread_helper+0x7/0x10
 =======================

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
kernel/hrtimer.c