[Xen-devel] One issue of pvops dom0's spinlock code

["Yang, Xiaowei" <xiaowei.yang@xxxxxxxxx>]

As we tested pvops dom0, sometimes we met some vCPUs hung due to dead lock. 
After checking the dom0's stack (see below) and the code, we found it's caused 
by this commit: 1e696f638 (xen: allow interrupts to be enabled while doing a 
blocking spin). If we don't enable irq inside spinlock slow path the issue is gone.
Jeremy,
Can you have a check of this?:)

Thanks,
Xiaowei

[ 2631.686041] Call Trace:
[ 2631.689073]  <IRQ>  [<ffffffff811a8b5f>] ? xen_poll_irq+0x49/0x53
[ 2631.695338]  [<ffffffff8100ff74>] xen_spin_lock_slow+0x13f/0x204
[ 2631.703151]  [<ffffffff810100ef>] xen_spin_lock_flags+0xb6/0xe6
[ 2631.709405]  [<ffffffff81050d68>] ? delayed_work_timer_fn+0x0/0x33
[ 2631.715663]  [<ffffffff813283ba>] _spin_lock_irqsave+0x30/0x39
[ 2631.723479]  [<ffffffff81050d42>] __queue_work+0x18/0x3e
[ 2631.728171]  [<ffffffff81050d97>] delayed_work_timer_fn+0x2f/0x33
[ 2631.735988]  [<ffffffff81049f41>] run_timer_softirq+0x160/0x1f1
[ 2631.743804]  [<ffffffff811a7488>] ? unmask_evtchn+0x34/0xd6
[ 2631.748493]  [<ffffffff81045f6f>] __do_softirq+0xa2/0x13d
[ 2631.754756]  [<ffffffff81013e0c>] call_softirq+0x1c/0x30
[ 2631.761007]  [<ffffffff81015950>] do_softirq+0x42/0x88
[ 2631.767262]  [<ffffffff81045ecb>] irq_exit+0x3f/0x41
[ 2631.771955]  [<ffffffff811a82af>] xen_evtchn_do_upcall+0x13e/0x15a
[ 2631.779774]  [<ffffffff81013e5e>] xen_do_hypervisor_callback+0x1e/0x30
[ 2631.787584]  <EOI>  [<ffffffff8100ff5d>] ? xen_spin_lock_slow+0x128/0x204
[ 2631.795407]  [<ffffffff810100ef>] ? xen_spin_lock_flags+0xb6/0xe6
[ 2631.801696]  [<ffffffff810862a4>] ? lru_add_drain_per_cpu+0x0/0xb
[ 2631.809483]  [<ffffffff813283ba>] ? _spin_lock_irqsave+0x30/0x39
[ 2631.815743]  [<ffffffff81328520>] ? _spin_unlock_irqrestore+0x27/0x2a
[ 2631.823557]  [<ffffffff81053fb3>] ? finish_wait+0x3b/0x67
[ 2631.828251]  [<ffffffff81050f7b>] ? worker_thread+0xb6/0x1f9
[ 2631.836067]  [<ffffffff81053e8e>] ? autoremove_wake_function+0x0/0x38
[ 2631.842325]  [<ffffffff81050ec5>] ? worker_thread+0x0/0x1f9
[ 2631.848576]  [<ffffffff81053aeb>] ? kthread+0x8f/0x97
[ 2631.854829]  [<ffffffff81013d0a>] ? child_rip+0xa/0x20
[ 2631.861083]  [<ffffffff81012ee7>] ? int_ret_from_sys_call+0x7/0x1b
[ 2631.867343]  [<ffffffff8101369d>] ? retint_restore_args+0x5/0x6
[ 2631.875159]  [<ffffffff81013d00>] ? child_rip+0x0/0x20


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