[Xen-devel] [PATCH for-4.13] x86/crash: force unlock console before printing on kexec crash

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
 xen/arch/x86/crash.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/arch/x86/crash.c b/xen/arch/x86/crash.c
index 6e1d3d3..a20ec8a 100644
--- a/xen/arch/x86/crash.c
+++ b/xen/arch/x86/crash.c
@@ -29,6 +29,7 @@
 #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 +156,7 @@ static void nmi_shootdown_cpus(void)
     }
 
     /* Leave a hint of how well we did trying to shoot down the other cpus */
+    console_force_unlock();
     if ( cpumask_empty(&waiting_to_crash) )
         printk("Shot down all CPUs\n");
     else
-- 
2.7.4


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