[PATCH -v2] IRQ, cpu-hotplug: Fix a race between CPU hotplug and IRQ desc alloc/free

[Huang, Ying]

From: Huang Ying <ying.huang@xxxxxxxxx>

When developing code to bootup some APs (Application CPUs)
asynchronously, the following kernel panic is encountered.  After
checking the code, it is found that the irq_to_desc() may return NULL
during CPU hotplug.  So the NULL pointer checking is added to fix
this.

"
BUG: unable to handle kernel NULL pointer dereference at 00000000000000a4
IP: _raw_spin_lock_irq+0x1e/0x40
PGD 0
P4D 0

Oops: 0002 [#1] SMP
Modules linked in:
CPU: 93 PID: 713 Comm: cpuhp/93 Not tainted 4.13.0-rc7-00261-g3760d3d #1
Hardware name: Intel Corporation BRICKLAND/BRICKLAND, BIOS BRBDXSD1.86B.0335.R00.1601291644 01/29/2016
task: ffff883f930e2680 task.stack: ffffc9000ef00000
RIP: 0010:_raw_spin_lock_irq+0x1e/0x40
RSP: 0000:ffffc9000ef03de0 EFLAGS: 00010046
RAX: 0000000000000000 RBX: 0000000000000010 RCX: 0000000000000010
RDX: 0000000000000001 RSI: 0000000000000010 RDI: 00000000000000a4
RBP: ffffc9000ef03de0 R08: ffff881036801240 R09: 0000000000000000
R10: 0000000000000040 R11: ffff881036801268 R12: 00000000000000a4
R13: 0000000000000000 R14: 000000000000005d R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff884044540000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000000a4 CR3: 000000407ee09000 CR4: 00000000003406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 irq_affinity_online_cpu+0x46/0xe0
 ? irq_migrate_all_off_this_cpu+0x2a0/0x2a0
 cpuhp_invoke_callback+0x80/0x400
 cpuhp_up_callbacks+0x36/0xc0
 ? smpboot_thread_fn+0x34/0x1f0
 ? smpboot_thread_fn+0x12d/0x1f0
 cpuhp_thread_fun+0xd5/0xe0
 smpboot_thread_fn+0x128/0x1f0
 kthread+0x114/0x150
 ? sort_range+0x30/0x30
 ? kthread_create_on_node+0x40/0x40
 ret_from_fork+0x25/0x30
Code: 89 e5 e8 26 8b 6f ff 5d c3 0f 1f 40 00 0f 1f 44 00 00 55 48 89 e5 fa 66 0f 1f 44 00 00 65 ff 05 49 4a 63 7e 31 c0 ba 01 00 00 00 <f0> 0f b1 17 85 c0 75 02 5d c3 89 c6 e8 21 71 6f ff 66 90 5d c3
RIP: _raw_spin_lock_irq+0x1e/0x40 RSP: ffffc9000ef03de0
CR2: 00000000000000a4
---[ end trace a9eacc0758f1f81e ]---
Kernel panic - not syncing: Fatal exception
"

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
---
 kernel/irq/cpuhotplug.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/irq/cpuhotplug.c b/kernel/irq/cpuhotplug.c
index 638eb9c83d9f..3c61c84efe59 100644
--- a/kernel/irq/cpuhotplug.c
+++ b/kernel/irq/cpuhotplug.c
@@ -133,6 +133,8 @@ void irq_migrate_all_off_this_cpu(void)
 		bool affinity_broken;
 
 		desc = irq_to_desc(irq);
+		if (!desc)
+			continue;
 		raw_spin_lock(&desc->lock);
 		affinity_broken = migrate_one_irq(desc);
 		raw_spin_unlock(&desc->lock);
@@ -179,6 +181,8 @@ int irq_affinity_online_cpu(unsigned int cpu)
 	irq_lock_sparse();
 	for_each_active_irq(irq) {
 		desc = irq_to_desc(irq);
+		if (!desc)
+			continue;
 		raw_spin_lock_irq(&desc->lock);
 		irq_restore_affinity_of_irq(desc, cpu);
 		raw_spin_unlock_irq(&desc->lock);
-- 
2.11.0