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

[Borislav Petkov]

On Fri, Jun 19, 2015 at 10:36:20AM -0700, Luck, Tony wrote:
> 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@xxxxxxxxx>
> Debugged-by: Borislav Petkov <bp@xxxxxxx>
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
>  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;

Hmm, and I was under the impression that mcheck_init() runs much
later... Not really.

Anyway, your version is better, I've replaced mine with it.

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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