Livepatch relies on stack checking of sleeping tasks to switch kthreads,
so a busy kthread can block a livepatch transition indefinitely. We've
seen this happen fairly often with busy vhost kthreads.

Add a check to call klp_switch_current() from vhost_worker() when a
livepatch is pending. In testing this allowed vhost kthreads to switch
immediately when they had previously blocked livepatch transitions for
long periods of time.

Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
---
 drivers/vhost/vhost.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index cbe72bfd2f1f..d8624f1f2d64 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c

@@ -30,6 +30,7 @@
 #include <linux/interval_tree_generic.h>
 #include <linux/nospec.h>
 #include <linux/kcov.h>
+#include <linux/livepatch.h>
 
 #include "vhost.h"
 

@@ -366,6 +367,9 @@ static int vhost_worker(void *data)
 			if (need_resched())
 				schedule();
 		}
+
+		if (unlikely(klp_patch_pending(current)))
+			klp_switch_current();
 	}
 	kthread_unuse_mm(dev->mm);
 	return 0;

-- 
b4 0.10.1