[Xen-changelog] [xen stable-4.12] x86/crash: force unlock console before printing on kexec crash

[patchbot@xxxxxxx]

commit e1424597956d7bfd506e05ea6f0b7e30e0582982
Author:     Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
AuthorDate: Fri Oct 25 11:40:17 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Oct 25 11:40:17 2019 +0200

    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@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 7d5247cee21aa38a16c4b21bc9243eda70c8aebd
    master date: 2019-10-02 11:25:05 +0100
---
 xen/arch/x86/crash.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/arch/x86/crash.c b/xen/arch/x86/crash.c
index a9f3e1890c..0165520724 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");
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12

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