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 d4fc136a86cf20a5398a24b55f3e0090d500039d..4db0758a884101bbe9da286a0437271515077bd8 100644 (file)
--- 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");