[PATCH] genirq: Avoid race between cpu hot plug and irq_desc() allocation paths

[Prakruthi Deepak Heragu]

One of the cores might have just allocated irq_desc() and other core
might be doing irq migration in the hot plug path. In the hot plug path
during the IRQ migration, for_each_active_irq macro is trying to get
irqs whose bits are set in allocated_irqs bit map but there is no return
value check after irq_to_desc for desc validity.

[   24.566381] msm_thermal:do_core_control Set Offline: CPU4 Temp: 73
[   24.568821] Unable to handle kernel NULL pointer dereference at virtual address 000000a4
[   24.568931] pgd = ffffffc002184000
[   24.568995] [000000a4] *pgd=0000000178df5003, *pud=0000000178df5003, *pmd=0000000178df6003, *pte=0060000017a00707
[   24.569153] ------------[ cut here ]------------
[   24.569228] Kernel BUG at ffffffc0000f3060 [verbose debug info unavailable]
[   24.569334] Internal error: Oops - BUG: 96000005 [#1] PREEMPT SMP
[   24.569422] Modules linked in:
[   24.569486] CPU: 4 PID: 28 Comm: migration/4 Tainted: G        W       4.4.8-perf-9407222-eng #1
[   24.569684] task: ffffffc0f28f0e80 ti: ffffffc0f2a84000 task.ti: ffffffc0f2a84000
[   24.569785] PC is at do_raw_spin_lock+0x20/0x160
[   24.569859] LR is at _raw_spin_lock+0x34/0x40
[   24.569931] pc : [<ffffffc0000f3060>] lr : [<ffffffc001023dec>] pstate: 200001c5
[   24.570029] sp : ffffffc0f2a87bc0
[   24.570091] x29: ffffffc0f2a87bc0 x28: ffffffc001033988
[   24.570174] x27: ffffffc001adebb0 x26: 0000000000000000
[   24.570257] x25: 00000000000000a0 x24: 0000000000000020
[   24.570339] x23: ffffffc001033978 x22: ffffffc001adeb80
[   24.570421] x21: 000000000000027e x20: 0000000000000000
[   24.570502] x19: 00000000000000a0 x18: 000000000000000d
[   24.570584] x17: 0000000000005f00 x16: 0000000000000003
[   24.570666] x15: 000000000000bd39 x14: 0ffffffffffffffe
[   24.570748] x13: 0000000000000000 x12: 0000000000000018
[   24.570829] x11: 0101010101010101 x10: 7f7f7f7f7f7f7f7f
[   24.570911] x9 : fefefefeff332e6d x8 : 7f7f7f7f7f7f7f7f
[   24.570993] x7 : ffffffc00344f6a0 x6 : 0000000000000000
[   24.571075] x5 : 0000000000000001 x4 : ffffffc00344f488
[   24.571157] x3 : 0000000000000000 x2 : 0000000000000000
[   24.571238] x1 : ffffffc0f2a84000 x0 : 0000000000004ead
...
...
...
[   24.581324] Call trace:
[   24.581379] [<ffffffc0000f3060>] do_raw_spin_lock+0x20/0x160
[   24.581463] [<ffffffc001023dec>] _raw_spin_lock+0x34/0x40
[   24.581546] [<ffffffc000103f10>] irq_migrate_all_off_this_cpu+0x84/0x1c4
[   24.581641] [<ffffffc00008ec84>] __cpu_disable+0x54/0x74
[   24.581722] [<ffffffc0000a3368>] take_cpu_down+0x1c/0x58
[   24.581803] [<ffffffc00013ac08>] multi_cpu_stop+0xb0/0x10c
[   24.581885] [<ffffffc00013ad60>] cpu_stopper_thread+0xb8/0x184
[   24.581972] [<ffffffc0000c4920>] smpboot_thread_fn+0x26c/0x290
[   24.582057] [<ffffffc0000c0f84>] kthread+0x100/0x108
[   24.582135] Code: aa0003f3 aa1e03e0 d503201f 5289d5a0 (b9400661)
[   24.582224] ---[ end trace 609f38584306f5d9 ]---

Signed-off-by: Prasad Sodagudi <psodagud@xxxxxxxxxxxxxx>
Signed-off-by: Prakruthi Deepak Heragu <pheragu@xxxxxxxxxxxxxx>
---
 kernel/irq/cpuhotplug.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/irq/cpuhotplug.c b/kernel/irq/cpuhotplug.c
index 5b1072e..17c5e71 100644
--- a/kernel/irq/cpuhotplug.c
+++ b/kernel/irq/cpuhotplug.c
@@ -160,6 +160,9 @@ 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);
-- 
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