[BUG 4.2-rc8] Interrupt occurs while apply_alternatives() is patching the handler

[Chuck Ebbert]

This is from https://bugzilla.redhat.com/show_bug.cgi?id=1258223

[    0.036000] BUG: unable to handle kernel paging request at 55501e06
[    0.036000] IP: [<c0aae48b>] common_interrupt+0xb/0x38
[    0.036000] *pde = 00000000 
[    0.036000] Oops: 0000 [#1] SMP 
[    0.036000] Modules linked in:
[    0.036000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.2.0-0.rc8.git3.1.fc24.i686 #1
[    0.036000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.2-20150714_191134- 04/01/2014
[    0.036000] task: c0d49ac0 ti: c0d42000 task.ti: c0d42000
[    0.036000] EIP: 0060:[<c0aae48b>] EFLAGS: 00200046 CPU: 0
[    0.036000] EIP is at common_interrupt+0xb/0x38
[    0.036000] EAX: c0aae480 EBX: 0000008d ECX: c0ab1c83 EDX: e4af6810
[    0.036000] ESI: 029a7802 EDI: 00000003 EBP: c0d43e68 ESP: c0d43e44
[    0.036000]  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
[    0.036000] CR0: 8005003b CR2: 55501e06 CR3: 00ebd000 CR4: 00000690
[    0.036000] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[    0.036000] DR6: 00000000 DR7: 00000000
[    0.036000] Stack:
[    0.036000]  0000004f c0409c80 00000060 00200202 00200046 c0d43e60 c0ea150c 029a7802
[    0.036000]  00000000 c0d43fb8 c040a054 c07f1cf0 6c0a1000 ffff0006 00200046 00000043
[    0.036000]  c0ed0bc0 00000000 c0d43e98 c071a6fc c0d43ea8 c0d43ec4 c0ea4c73 c0ea4c7f
[    0.036000] Call Trace:
[    0.036000]  [<c0409c80>] ? add_nops+0x90/0xa0
[    0.036000]  [<c040a054>] apply_alternatives+0x274/0x630
[    0.036000]  [<c07f1cf0>] ? wait_for_xmitr+0xa0/0xa0
[    0.036000]  [<c071a6fc>] ? sprintf+0x1c/0x20
[    0.036000]  [<c0aae480>] ? irq_entries_start+0x698/0x698
[    0.036000]  [<c071be4b>] ? memcpy+0xb/0x30
[    0.036000]  [<c07f3950>] ? serial8250_set_termios+0x20/0x20
[    0.036000]  [<c0aad4e3>] ? _raw_write_unlock_irqrestore+0x13/0x20
[    0.036000]  [<c0aad4e3>] ? _raw_write_unlock_irqrestore+0x13/0x20
[    0.036000]  [<c0aad4fd>] ? _raw_spin_unlock_irqrestore+0xd/0x10
[    0.036000]  [<c04b17b9>] ? console_unlock+0x2e9/0x610
[    0.036000]  [<c04b03cd>] ? log_store+0x1cd/0x210
[    0.036000]  [<c04b1d7e>] ? vprintk_emit+0x29e/0x570
[    0.036000]  [<c04b21e1>] ? vprintk_default+0x41/0x60
[    0.036000]  [<c0aa7725>] ? printk+0x17/0x19
[    0.036000]  [<c0dfdd48>] ? identify_boot_cpu+0x7b/0x80
[    0.036000]  [<c0dfca47>] alternative_instructions+0x17/0xc1
[    0.036000]  [<c0dfdda9>] check_bugs+0x32/0x39
[    0.036000]  [<c0df6b57>] start_kernel+0x3ca/0x40a
[    0.036000]  [<c0df62e3>] i386_start_kernel+0x91/0x95
[    0.036000] Code: 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 8d 90 90 83 04 24 80 fc 0f a8 0f <a0> 06 1e 50 55 57 56 52 51 53 ba 7b 00 00 00 8e da 8e c2 ba d8

   0:	8d 90 90 83 04 24    	lea    0x24048390(%eax),%edx
   6:	80 fc 0f             	cmp    $0xf,%ah
   9:	a8 0f                	test   $0xf,%al
>> b:	a0 06 1e 50 55       	mov    0x55501e06,%al
  10:	57                   	push   %edi
  11:	56                   	push   %esi

Interrupt 0x30 occurred while the alternatives code was replacing the
initial 0x90,0x90,0x90 NOPs (from the ASM_CLAC macro) with the optimized
version, 0x8d,0x76,0x00. Only the first byte has been replaced so far,
and it makes a mess out of the insn decoding.

I have no clue how to fix this.
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