Patch "xen/x86: fix cpu hotplug" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

xen/x86: fix cpu hotplug

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xen-x86-fix-cpu-hotplug.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Juergen Gross <[email protected]>
Date: Wed, 5 Jul 2017 16:05:20 +0200
Subject: xen/x86: fix cpu hotplug

From: Juergen Gross <[email protected]>

commit c185ddec54657c145a0c2055e4b87918da24974f upstream.

Commit dc6416f1d711eb4c1726e845d653235dcaae12e1 ("xen/x86: Call cpu_startup_entry(CPUHP_AP_ONLINE_IDLE) from xen_play_dead()") introduced an error leading to a stack overflow of the idle task when a cpu was brought offline/online many times: by calling cpu_startup_entry() instead of returning at the end of xen_play_dead() do_idle() would be entered again and again.

Don't use cpu_startup_entry(), but cpuhp_online_idle() instead allowing to return from xen_play_dead().

---
 arch/x86/xen/smp_pv.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -19,6 +19,7 @@
 #include <linux/irq_work.h>
 #include <linux/tick.h>
 #include <linux/nmi.h>
+#include <linux/cpuhotplug.h>
 
 #include <asm/paravirt.h>
 #include <asm/desc.h>

@@ -417,7 +418,7 @@ static void xen_pv_play_dead(void) /* us
 	 */
 	tick_nohz_idle_enter();
 
-	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
+	cpuhp_online_idle(CPUHP_AP_ONLINE_IDLE);
 }
 
 #else /* !CONFIG_HOTPLUG_CPU */

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/xen-x86-fix-cpu-hotplug.patch queue-4.12/xen-scsiback-fix-a-tmr-related-use-after-free.patch