iommu/vt-d: clean up pr_irq if request_threaded_irq fails

It is unlikely request_threaded_irq will fail, but if it does for some
reason we should clear iommu->pr_irq in the error path. Also
intel_svm_finish_prq shouldn't try to clean up the page request
interrupt if pr_irq is 0. Without these, if request_threaded_irq were
to fail the following occurs:

fail with no fixes:

[    0.683147] ------------[ cut here ]------------
[    0.683148] NULL pointer, cannot free irq
[    0.683158] WARNING: CPU: 1 PID: 1 at kernel/irq/irqdomain.c:1632 irq_domain_free_irqs+0x126/0x140
[    0.683160] Modules linked in:
[    0.683163] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.15.0-rc2 #3
[    0.683165] Hardware name:                  /NUC7i3BNB, BIOS BNKBL357.86A.0036.2017.0105.1112 01/05/2017
[    0.683168] RIP: 0010:irq_domain_free_irqs+0x126/0x140
[    0.683169] RSP: 0000:ffffc90000037ce8 EFLAGS: 00010292
[    0.683171] RAX: 000000000000001d RBX: ffff880276283c00 RCX: ffffffff81c5e5e8
[    0.683172] RDX: 0000000000000001 RSI: 0000000000000096 RDI: 0000000000000246
[    0.683174] RBP: ffff880276283c00 R08: 0000000000000000 R09: 000000000000023c
[    0.683175] R10: 0000000000000007 R11: 0000000000000000 R12: 000000000000007a
[    0.683176] R13: 0000000000000001 R14: 0000000000000000 R15: 0000010010000000
[    0.683178] FS:  0000000000000000(0000) GS:ffff88027ec80000(0000) knlGS:0000000000000000
[    0.683180] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.683181] CR2: 0000000000000000 CR3: 0000000001c09001 CR4: 00000000003606e0
[    0.683182] Call Trace:
[    0.683189]  intel_svm_finish_prq+0x3c/0x60
[    0.683191]  free_dmar_iommu+0x1ac/0x1b0
[    0.683195]  init_dmars+0xaaa/0xaea
[    0.683200]  ? klist_next+0x19/0xc0
[    0.683203]  ? pci_do_find_bus+0x50/0x50
[    0.683205]  ? pci_get_dev_by_id+0x52/0x70
[    0.683208]  intel_iommu_init+0x498/0x5c7
[    0.683211]  pci_iommu_init+0x13/0x3c
[    0.683214]  ? e820__memblock_setup+0x61/0x61
[    0.683217]  do_one_initcall+0x4d/0x1a0
[    0.683220]  kernel_init_freeable+0x186/0x20e
[    0.683222]  ? set_debug_rodata+0x11/0x11
[    0.683225]  ? rest_init+0xb0/0xb0
[    0.683226]  kernel_init+0xa/0xff
[    0.683229]  ret_from_fork+0x1f/0x30
[    0.683259] Code: 89 ee 44 89 e7 e8 3b e8 ff ff 5b 5d 44 89 e7 44 89 ee 41 5c 41 5d 41 5e e9 a8 84 ff ff 48 c7 c7 a8 71 a7 81 31 c0 e8 6a d3 f9 ff <0f> ff 5b 5d 41 5c 41 5d 41 5
e c3 0f 1f 44 00 00 66 2e 0f 1f 84
[    0.683285] ---[ end trace f7650e42792627ca ]---

with iommu->pr_irq = 0, but no check in intel_svm_finish_prq:

[    0.669561] ------------[ cut here ]------------
[    0.669563] Trying to free already-free IRQ 0
[    0.669573] WARNING: CPU: 3 PID: 1 at kernel/irq/manage.c:1546 __free_irq+0xa4/0x2c0
[    0.669574] Modules linked in:
[    0.669577] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 4.15.0-rc2 #4
[    0.669579] Hardware name:                  /NUC7i3BNB, BIOS BNKBL357.86A.0036.2017.0105.1112 01/05/2017
[    0.669581] RIP: 0010:__free_irq+0xa4/0x2c0
[    0.669582] RSP: 0000:ffffc90000037cc0 EFLAGS: 00010082
[    0.669584] RAX: 0000000000000021 RBX: 0000000000000000 RCX: ffffffff81c5e5e8
[    0.669585] RDX: 0000000000000001 RSI: 0000000000000086 RDI: 0000000000000046
[    0.669587] RBP: 0000000000000000 R08: 0000000000000000 R09: 000000000000023c
[    0.669588] R10: 0000000000000007 R11: 0000000000000000 R12: ffff880276253960
[    0.669589] R13: ffff8802762538a4 R14: ffff880276253800 R15: ffff880276283600
[    0.669593] FS:  0000000000000000(0000) GS:ffff88027ed80000(0000) knlGS:0000000000000000
[    0.669594] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.669596] CR2: 0000000000000000 CR3: 0000000001c09001 CR4: 00000000003606e0
[    0.669602] Call Trace:
[    0.669616]  free_irq+0x30/0x60
[    0.669620]  intel_svm_finish_prq+0x34/0x60
[    0.669623]  free_dmar_iommu+0x1ac/0x1b0
[    0.669627]  init_dmars+0xaaa/0xaea
[    0.669631]  ? klist_next+0x19/0xc0
[    0.669634]  ? pci_do_find_bus+0x50/0x50
[    0.669637]  ? pci_get_dev_by_id+0x52/0x70
[    0.669639]  intel_iommu_init+0x498/0x5c7
[    0.669642]  pci_iommu_init+0x13/0x3c
[    0.669645]  ? e820__memblock_setup+0x61/0x61
[    0.669648]  do_one_initcall+0x4d/0x1a0
[    0.669651]  kernel_init_freeable+0x186/0x20e
[    0.669653]  ? set_debug_rodata+0x11/0x11
[    0.669656]  ? rest_init+0xb0/0xb0
[    0.669658]  kernel_init+0xa/0xff
[    0.669661]  ret_from_fork+0x1f/0x30
[    0.669662] Code: 7a 08 75 0e e9 c3 01 00 00 4c 39 7b 08 74 57 48 89 da 48 8b 5a 18 48 85 db 75 ee 89 ee 48 c7 c7 78 67 a7 81 31 c0 e8 4c 37 fa ff <0f> ff 48 8b 34 24 4c 89 ef e
8 0e 4c 68 00 49 8b 46 40 48 8b 80
[    0.669688] ---[ end trace 58a470248700f2fc ]---

Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/iommu/intel-svm.c

@@ -129,6 +129,7 @@ int intel_svm_enable_prq(struct intel_iommu *iommu)
 		pr_err("IOMMU: %s: Failed to request IRQ for page request queue\n",
 		       iommu->name);
 		dmar_free_hwirq(irq);
+		iommu->pr_irq = 0;
 		goto err;
 	}
 	dmar_writeq(iommu->reg + DMAR_PQH_REG, 0ULL);
@@ -144,9 +145,11 @@ int intel_svm_finish_prq(struct intel_iommu *iommu)
 	dmar_writeq(iommu->reg + DMAR_PQT_REG, 0ULL);
 	dmar_writeq(iommu->reg + DMAR_PQA_REG, 0ULL);
 
-	free_irq(iommu->pr_irq, iommu);
-	dmar_free_hwirq(iommu->pr_irq);
-	iommu->pr_irq = 0;
+	if (iommu->pr_irq) {
+		free_irq(iommu->pr_irq, iommu);
+		dmar_free_hwirq(iommu->pr_irq);
+		iommu->pr_irq = 0;
+	}
 
 	free_pages((unsigned long)iommu->prq, PRQ_ORDER);
 	iommu->prq = NULL;