linux-kernel - [PATCH] x86/xen: Return from panic notifier

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Date:   Tue,  1 Oct 2019 11:16:33 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     jgross@...e.com, james@...gwall.me.uk,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: [PATCH] x86/xen: Return from panic notifier

Currently execution of panic() continues until Xen's panic notifier
(xen_panic_event()) is called at which point we make a hypercall that
never returns.

This means that any notifier that is supposed to be called later as
well as significant part of panic() code (such as pstore writes from
kmsg_dump()) is never executed.

There is no reason for xen_panic_event() to be this last point in
execution since panic()'s emergency_restart() will call into
xen_emergency_restart() from where we can perform our hypercall.

Reported-by: James Dingwall <james@...gwall.me.uk>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
---
 arch/x86/xen/enlighten.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 750f46ad018a..fd4f58cf51dc 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -269,16 +269,27 @@ void xen_reboot(int reason)
 		BUG();
 }
 
+static int reboot_reason = SHUTDOWN_reboot;
 void xen_emergency_restart(void)
 {
-	xen_reboot(SHUTDOWN_reboot);
+	xen_reboot(reboot_reason);
 }
 
 static int
 xen_panic_event(struct notifier_block *this, unsigned long event, void *ptr)
 {
-	if (!kexec_crash_loaded())
-		xen_reboot(SHUTDOWN_crash);
+	if (!kexec_crash_loaded()) {
+		reboot_reason = SHUTDOWN_crash;
+
+		/*
+		 * If panic_timeout==0 then we are supposed to wait forever.
+		 * However, to preserve original dom0 behavior we have to drop
+		 * into hypervisor. (domU behavior is controlled by its
+		 * config file)
+		 */
+		if (panic_timeout == 0)
+			panic_timeout = -1;
+	}
 	return NOTIFY_DONE;
 }
 
-- 
2.17.1