From: Igor Druzhinin <igor.druzhinin@citrix.com>
Date: Fri, 25 Oct 2019 10:00:09 +0000 (+0200)
Subject: x86/crash: force unlock console before printing on kexec crash
X-Git-Tag: archive/raspbian/4.11.3+24-g14b62ab3e5-1+rpi1^2~55^2~94
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=ba6f5bea6d725a3e5358108731ffc5fd1594b754;p=xen.git

x86/crash: force unlock console before printing on kexec crash

There is a small window where shootdown NMI might come to a CPU
(e.g. in serial interrupt handler) where console lock is taken. In order
not to leave following console prints waiting infinitely for shot down
CPUs to free the lock - force unlock the console.

The race has been frequently observed while crashing nested Xen in
an HVM domain.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 7d5247cee21aa38a16c4b21bc9243eda70c8aebd
master date: 2019-10-02 11:25:05 +0100
---

diff --git a/xen/arch/x86/crash.c b/xen/arch/x86/crash.c
index d4fc136a86..4db0758a88 100644
--- a/xen/arch/x86/crash.c
+++ b/xen/arch/x86/crash.c
@@ -30,6 +30,7 @@
 #include <asm/io_apic.h>
 #include <xen/iommu.h>
 #include <asm/hpet.h>
+#include <xen/console.h>
 
 static cpumask_t waiting_to_crash;
 static unsigned int crashing_cpu;
@@ -155,6 +156,12 @@ static void nmi_shootdown_cpus(void)
         msecs--;
     }
 
+    /*
+     * We may have NMI'd another CPU while it was holding the console lock.
+     * It won't be in a position to release the lock...
+     */
+    console_force_unlock();
+
     /* Leave a hint of how well we did trying to shoot down the other cpus */
     if ( cpumask_empty(&waiting_to_crash) )
         printk("Shot down all CPUs\n");