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From:   "Seth Forshee (DigitalOcean)" <sforshee@digitalocean.com>
Date:   Fri, 20 Jan 2023 16:12:22 -0600
Subject: [PATCH 2/2] vhost: check for pending livepatches from vhost worker
 kthreads
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Message-Id: <20230120-vhost-klp-switching-v1-2-7c2b65519c43@kernel.org>
References: <20230120-vhost-klp-switching-v1-0-7c2b65519c43@kernel.org>
In-Reply-To: <20230120-vhost-klp-switching-v1-0-7c2b65519c43@kernel.org>
To:     Petr Mladek <pmladek@suse.com>, Jason Wang <jasowang@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jiri Kosina <jikos@kernel.org>,
        Miroslav Benes <mbenes@suse.cz>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>
Cc:     virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
        "Seth Forshee (DigitalOcean)" <sforshee@kernel.org>,
        netdev@vger.kernel.org, live-patching@vger.kernel.org,
        linux-kernel@vger.kernel.org
Precedence: bulk

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