Promote one fix for 3.16 This fix was necessary after 9c15a24b038f ("x86/mce: Improve mcheck_init_device() error handling") went in. What this patch did was, among others, check the return value of misc_register and exit early if it encountered an error. Original code sloppily didn't do that. However, cef12ee52b05 ("xen/mce: Add mcelog support for Xen platform") made it so that xen's init routine xen_late_init_mcelog runs first. This was needed for the xen mcelog device which is supposed to be independent from the baremetal one. Initially it was reported that misc_register() fails often on xen and that's why it needed fixing. However, it is *supposed* to fail by design, when running in dom0 so that the xen mcelog device file gets registered first. And *then* you need the notifier *not* unregistered on the error path so that the timer does get deleted properly in the CPU hotplug notifier. Btw, this fix is needed also on baremetal in the unlikely event that misc_register(&mce_chrdev_device) fails there too. I was unsure whether to rush it in now and decided to delay it to 3.17. However, xen people wanted it promoted as it breaks xen when doing cpu hotplug there. So, after a bit of simmering in tip/master for initial smoke testing, let's move it to 3.16. It fixes a semi-regression which got introduced in 3.16 so no need for stable tagging. tip/x86/ras contains that exact same commit but we can't remove it there as it is not the last one. It won't cause any merge issues, as I confirmed locally but I should state here the special situation of this one fix explicitly anyway. Thanks.
Unified · Split
| @@ -2451,6 +2451,12 @@ static __init int mcheck_init_device(void) · 2450 unmodified lines | ||
| 2451 | 2451 | for_each_online_cpu(i) { |
| 2452 | 2452 | err = mce_device_create(i); |
| 2453 | 2453 | if (err) { |
| 2454 | + /* | |
| 2455 | + * Register notifier anyway (and do not unreg it) so | |
| 2456 | + * that we don't leave undeleted timers, see notifier | |
| 2457 | + * callback above. | |
| 2458 | + */ | |
| 2459 | + __register_hotcpu_notifier(&mce_cpu_notifier); | |
| 2454 | 2460 | cpu_notifier_register_done(); |
| 2455 | 2461 | goto err_device_create; |
| 2456 | 2462 | } |
| @@ -2471,10 +2477,6 @@ static __init int mcheck_init_device(void) · 14 unmodified lines | ||
| 2471 | 2477 | err_register: |
| 2472 | 2478 | unregister_syscore_ops(&mce_syscore_ops); |
| 2473 | 2479 | |
| 2474 | − cpu_notifier_register_begin(); | |
| 2475 | − __unregister_hotcpu_notifier(&mce_cpu_notifier); | |
| 2476 | − cpu_notifier_register_done(); | |
| 2477 | − | |
| 2478 | 2480 | err_device_create: |
| 2479 | 2481 | /* |
| 2480 | 2482 | * We didn't keep track of which devices were created above, but |