On 01/10/2019 20:15, Igor Druzhinin wrote:
> 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.druzhi...@citrix.com>
> ---
> 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
The overall change, R-by me, but I'd prefer something along the lines of:
diff --git a/xen/arch/x86/crash.c b/xen/arch/x86/crash.c
index 6e1d3d3a84..41687465ac 100644
--- a/xen/arch/x86/crash.c
+++ b/xen/arch/x86/crash.c
@@ -154,6 +154,12 @@ 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");
If you're happy, I can fold this in on commit.
~Andrew
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