[PATCH 4.14-rt] Fix wrong-variable use in irq_set_affinity_notifier

[Joe Korty <joe.korty@xxxxxxxxxxxxxxxxx>]

4.14-rt: Fix wrong-variable use in irq_set_affinity_notifier.

The bug was introduced in the 4.14-rt patch
 
   0461-genirq-Handle-missing-work_struct-in-irq_set_affinit.patch

The symptom is a NULL pointer panic in the i40e driver on
system shutdown.

    Rebooting.
    BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
    IP: __kthread_cancel_work_sync+0x12/0xa0
    CPU: 15 PID: 6274 Comm: reboot Not tainted 4.14.155-rt70-RedHawk-8.0.2-prt-trace #1
    task: ffff9ef0d1a58000 task.stack: ffffbe540c038000
    RIP: 0010:__kthread_cancel_work_sync+0x12/0xa0
    RSP: 0018:ffffbe540c03bbd8 EFLAGS: 00010296
    RAX: 0000084000000020 RBX: 0000000000000000 RCX: 0000000000000034
    RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000008
    RBP: ffffbe540c03bc00 R08: ffff9ee8ccdc3800 R09: ffff9ef0d8c0c000
    R10: ffff9ef0d8c0c028 R11: 0000000000000040 R12: ffff9ee8ccdc3800
    R13: 0000000000000000 R14: ffff9ee8ccdc3960 R15: 0000000000000074
    FS:  00007ffff7fcf380(0000) GS:ffff9ef0ffdc0000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000000000000020 CR3: 000000104b428003 CR4: 00000000005606e0
    DR0: 00000000006040e0 DR1: 00000000006040e8 DR2: 00000000006040f0
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
    PKRU: 55555554

    Call Trace:
     kthread_cancel_work_sync+0xb/0x10
     irq_set_affinity_notifier+0x8e/0xc0
     i40e_vsi_free_irq+0xbc/0x230 [i40e]
     i40e_vsi_close+0x24/0xa0 [i40e]
     i40e_close+0x10/0x20 [i40e]
     i40e_quiesce_vsi.part.40+0x30/0x40 [i40e]
     i40e_pf_quiesce_all_vsi.isra.41+0x34/0x50 [i40e]
     i40e_prep_for_reset+0x67/0x110 [i40e]
     i40e_shutdown+0x39/0x220 [i40e]
     pci_device_shutdown+0x2b/0x50
     device_shutdown+0x147/0x1f0
     kernel_restart_prepare+0x71/0x74
     kernel_restart+0xd/0x4e
     SyS_reboot.cold.1+0x9/0x34
     do_syscall_64+0x7c/0x150

4.19-rt and above do not have this problem due to a refactoring.

Signed-off-by: Joe Korty <Joe.Korty@xxxxxxxxxxxxxxxxx>

Index: b/kernel/irq/manage.c
===================================================================
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -353,7 +353,7 @@ irq_set_affinity_notifier(unsigned int i
 
 	if (old_notify) {
 #ifdef CONFIG_PREEMPT_RT_BASE
-		kthread_cancel_work_sync(&notify->work);
+		kthread_cancel_work_sync(&old_notify->work);
 #else
 		cancel_work_sync(&old_notify->work);
 #endif