xen_console_resume() may sleep with irqs disabled

[David Vrabel <david.vrabel@citrix.com>]

During a suspend/resume cycle (e.g., a migration), xen_console_resume()
is called from xen_suspend() which is called with local irqs disabled by
stop_machine().

xen_console_resume() calls rebind_evtchn_irq() which attempts to lock
the irq_mapping_update_lock mutex.  This produces the BUG listed below.

The lock was changed to a mutex by 773659 (xen/irq: Alter the locking to
use a mutex instead of a spinlock.).  Clearly we can't just revert this
change but it's not clear to me what the correct fix here is.

Can xen_console_resume() be deferred to later in the resume process?

David

[   39.877210] BUG: sleeping function called from invalid context at
/anfs/drall/scratch/davidvr/x86/linux/kernel/mutex.c:413
[   39.877210] in_atomic(): 1, irqs_disabled(): 1, pid: 7, name: migration/0
[   39.877210] no locks held by migration/0/7.
[   39.877210] irq event stamp: 38
[   39.877210] hardirqs last  enabled at (37): [<ffffffff812d07b0>]
_raw_spin_unlock_irq+0x30/0x50
[   39.877210] hardirqs last disabled at (38): [<ffffffff81091ab5>]
stop_machine_cpu_stop+0x95/0x110
[   39.877210] softirqs last  enabled at (0): [<ffffffff8103cd98>]
copy_process.part.63+0x348/0x13e0
[   39.877210] softirqs last disabled at (0): [<          (null)>]
     (null)
[   39.877210] CPU: 0 PID: 7 Comm: migration/0 Not tainted
3.10.0-rc6.davidvr #82
[   39.877210]  0000000000000000 ffff88000ec8fbc8 ffffffff812cc2cf
ffff88000ec8fbe8
[   39.877210]  ffffffff810723b5 ffff88000ed16800 ffff88000ec8ffd8
ffff88000ec8fc68
[   39.877210]  ffffffff812cd181 ffff88000ec8fc18 ffffffff81092b17
ffff88000ed16800
[   39.877210] Call Trace:
[   39.877210]  [<ffffffff812cc2cf>] dump_stack+0x19/0x1b
[   39.877210]  [<ffffffff810723b5>] __might_sleep+0xf5/0x130
[   39.877210]  [<ffffffff812cd181>] mutex_lock_nested+0x41/0x3b0
[   39.877210]  [<ffffffff81092b17>] ? __irq_put_desc_unlock+0x27/0x50
[   39.877210]  [<ffffffff8109410c>] ? __disable_irq_nosync+0x4c/0x70
[   39.877210]  [<ffffffff81091a01>] ? queue_stop_cpus_work+0xc1/0xe0
[   39.877210]  [<ffffffff811bc912>] rebind_evtchn_irq+0x42/0xc0
[   39.877210]  [<ffffffff811e3c80>] xen_console_resume+0x60/0x70
[   39.877210]  [<ffffffff811b87c2>] xen_suspend+0x92/0xb0
[   39.877210]  [<ffffffff81091acb>] stop_machine_cpu_stop+0xab/0x110
[   39.877210]  [<ffffffff81091a20>] ? queue_stop_cpus_work+0xe0/0xe0
[   39.877210]  [<ffffffff8109170b>] cpu_stopper_thread+0x8b/0x140
[   39.877210]  [<ffffffff812d073f>] ? _raw_spin_unlock_irqrestore+0x3f/0x80
[   39.877210]  [<ffffffff81086f25>] ? trace_hardirqs_on_caller+0x105/0x1d0
[   39.877210]  [<ffffffff81086ffd>] ? trace_hardirqs_on+0xd/0x10
[   39.877210]  [<ffffffff812d0749>] ? _raw_spin_unlock_irqrestore+0x49/0x80
[   39.877210]  [<ffffffff8106a6c6>] smpboot_thread_fn+0x166/0x1f0
[   39.877210]  [<ffffffff8106a560>] ? lg_global_unlock+0x80/0x80
[   39.877210]  [<ffffffff8106271b>] kthread+0xdb/0xe0
[   39.877210]  [<ffffffff81062640>] ? __kthread_parkme+0x90/0x90
[   39.877210]  [<ffffffff812d1eac>] ret_from_fork+0x7c/0xb0
[   39.877210]  [<ffffffff81062640>] ? __kthread_parkme+0x90/0x90