commit f0f39387 upstream.

Commit ff1e22e7 ("xen/events: Mask a moving irq") open-coded
irq_move_irq() but left out checking if the IRQ is disabled. This broke
resuming from suspend since it tries to move a (disabled) irq without
holding the IRQ's desc->lock. Fix it by adding in a check for disabled
IRQs.

The resulting stacktrace was:
kernel BUG at /build/linux-UbQGH5/linux-4.4.0/kernel/irq/migration.c:31!
invalid opcode: 0000 [#1] SMP
Modules linked in: xenfs xen_privcmd ...
CPU: 0 PID: 9 Comm: migration/0 Not tainted 4.4.0-22-generic #39-Ubuntu
Hardware name: Xen HVM domU, BIOS 4.6.1-xs125180 05/04/2016
task: ffff88003d75ee00 ti: ffff88003d7bc000 task.ti: ffff88003d7bc000
RIP: 0010:[<ffffffff810e26e2>]  [<ffffffff810e26e2>] irq_move_masked_irq+0xd2/0xe0
RSP: 0018:ffff88003d7bfc50  EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff88003d40ba00 RCX: 0000000000000001
RDX: 0000000000000001 RSI: 0000000000000100 RDI: ffff88003d40bad8
RBP: ffff88003d7bfc68 R08: 0000000000000000 R09: ffff88003d000000
R10: 0000000000000000 R11: 000000000000023c R12: ffff88003d40bad0
R13: ffffffff81f3a4a0 R14: 0000000000000010 R15: 00000000ffffffff
FS:  0000000000000000(0000) GS:ffff88003da00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd4264de624 CR3: 0000000037922000 CR4: 00000000003406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff88003d40ba38 0000000000000024 0000000000000000 ffff88003d7bfca0
 ffffffff814c8d92 00000010813ef89d 00000000805ea732 0000000000000009
 0000000000000024 ffff88003cc39b80 ffff88003d7bfce0 ffffffff814c8f66
Call Trace:
 [<ffffffff814c8d92>] eoi_pirq+0xb2/0xf0
 [<ffffffff814c8f66>] __startup_pirq+0xe6/0x150
 [<ffffffff814ca659>] xen_irq_resume+0x319/0x360
 [<ffffffff814c7e75>] xen_suspend+0xb5/0x180
 [<ffffffff81120155>] multi_cpu_stop+0xb5/0xe0
 [<ffffffff811200a0>] ? cpu_stop_queue_work+0x80/0x80
 [<ffffffff811203d0>] cpu_stopper_thread+0xb0/0x140
 [<ffffffff810a94e6>] ? finish_task_switch+0x76/0x220
 [<ffffffff810ca731>] ? __raw_callee_save___pv_queued_spin_unlock+0x11/0x20
 [<ffffffff810a3935>] smpboot_thread_fn+0x105/0x160
 [<ffffffff810a3830>] ? sort_range+0x30/0x30
 [<ffffffff810a0588>] kthread+0xd8/0xf0
 [<ffffffff810a04b0>] ? kthread_create_on_node+0x1e0/0x1e0
 [<ffffffff8182568f>] ret_from_fork+0x3f/0x70
 [<ffffffff810a04b0>] ? kthread_create_on_node+0x1e0/0x1e0
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>