Re: [PATCH] x86/mce: Initialize workqueues only once (alternate proposal)

["Luck, Tony" <tony.luck@intel.com>]

96d98bfd0366 ("x86/mce: Don't use percpu workqueues") dropped the
per-CPU workqueues in the MCE code but left the initialization per-CPU.
This lead to early boot time splats (below) in the workqueues code
because we were overwriting the workqueue during INIT_WORK() on each new
CPU which would appear.

Move initialization to mcheck_init() so it happens only once.

  mce: [Hardware Error]: Machine check events logged
  BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
  IP: [<ffffffff810980a1>] process_one_work+0x31/0x420
   PGD 0
  Oops: 0000 [#1] SMP
  Modules linked in:
  CPU: 36 PID: 263 Comm: kworker/36:0 Not tainted 4.1.0-rc8 #1
  Hardware name: Intel Corporation BRICKLAND/BRICKLAND, BIOS BRHSXSD1.86B.0065.R01.1505011640
+05/01/2015
  task: ffff88181c284470 ti: ffff88181bd94000 task.ti: ffff88181bd94000
  RIP: 0010:[<ffffffff810980a1>] process_one_work+0x31/0x420
  RSP: 0000:ffff88181bd97e08  EFLAGS: 00010046
  RAX: 0000000fffffffe0 RBX: ffffffff81d0fa20 RCX: 0000000000000000
  RDX: 0000000fffffff00 RSI: ffffffff81d0fa20 RDI: ffff88181c2660c0
  RBP: ffff88181bd97e48 R08: ffff88181f416ec0 R09: ffff88181c284470
  R10: 0000000000000002 R11: ffffffff8109e5ac R12: ffff88181c2660c0
  R13: ffff88181f416ec0 R14: 0000000000000000 R15: ffff88181c2660f0
                             ^^^^^^^^^^^^^^^^^

  27:   4c 0f 45 f2             cmovne %rdx,%r14
  2b:*  49 8b 46 08             mov    0x8(%r14),%rax           <-- trapping instruction
  2f:   44 8b b8 00 01 00 00    mov    0x100(%rax),%r15d

  ...

  Call Trace:
   worker_thread
   ? rescuer_thread
   kthread
   ? kthread_create_on_node
   ret_from_fork
   ? kthread_create_on_node
  Code: 48 89 e5 41 57 41 56 45 31 f6 41 55 41 54 49 89 fc 53 48 89 f3 48 83 ec 18 48 8b 06 4c
+8b 6f 48 48 89 c2 30 d2 a8 04 4c 0f 45 f2 <49> 8b 46 08 44 8b b8 00 01 00 00 41 c1 ef 05 44
+89 f8 83 e0 01
  RIP  [<ffffffff810980a1>] process_one_work
   RSP <ffff88181bd97e08>
  CR2: 0000000000000008
  ---[ end trace 8229a011b97532a0 ]---
  Kernel panic - not syncing: Fatal exception
  ---[ end Kernel panic - not syncing: Fatal exception

Reported-by: Rui Wang <rui.y.wang@intel.com>
Debugged-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 478f81a6d824..158d9e7db974 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1665,9 +1665,6 @@ void mcheck_cpu_init(struct cpuinfo_x86 *c)
 		return;
 	}
 
-	INIT_WORK(&mce_work, mce_process_work);
-	init_irq_work(&mce_irq_work, mce_irq_work_cb);
-
 	machine_check_vector = do_machine_check;
 
 	__mcheck_cpu_init_generic();
@@ -1994,6 +1991,9 @@ int __init mcheck_init(void)
 	mce_register_decode_chain(&mce_srao_nb);
 	mcheck_vendor_init_severity();
 
+	INIT_WORK(&mce_work, mce_process_work);
+	init_irq_work(&mce_irq_work, mce_irq_work_cb);
+
 	return 0;
 }
 
-- 
2.1.4

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