linux-kernel - [PATCH] arm/xen: Don't probe xenbus as part of an early initcall

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Date:   Wed, 10 Feb 2021 17:06:54 +0000
From:   Julien Grall <julien@....org>
To:     xen-devel@...ts.xenproject.org
Cc:     sstabellini@...nel.org, boris.ostrovsky@...cle.com,
        jgross@...e.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Julien Grall <jgrall@...zon.com>,
        Ian Jackson <iwj@...project.org>, dwmw@...zon.co.uk
Subject: [PATCH] arm/xen: Don't probe xenbus as part of an early initcall

From: Julien Grall <jgrall@...zon.com>

After Commit 3499ba8198cad ("xen: Fix event channel callback via
INTX/GSI"), xenbus_probe() will be called too early on Arm. This will
recent to a guest hang during boot.

If there hang wasn't there, we would have ended up to call
xenbus_probe() twice (the second time is in xenbus_probe_initcall()).

We don't need to initialize xenbus_probe() early for Arm guest.
Therefore, the call in xen_guest_init() is now removed.

After this change, there is no more external caller for xenbus_probe().
So the function is turned to a static one. Interestingly there were two
prototypes for it.

Fixes: 3499ba8198cad ("xen: Fix event channel callback via INTX/GSI")
Reported-by: Ian Jackson <iwj@...project.org>
Signed-off-by: Julien Grall <jgrall@...zon.com>

CC: dwmw@...zon.co.uk

---

The offending commit unfortunately got backport to stable trees. So
this will need to be backported as well.
---
 arch/arm/xen/enlighten.c          | 2 --
 drivers/xen/xenbus/xenbus.h       | 1 -
 drivers/xen/xenbus/xenbus_probe.c | 2 +-
 include/xen/xenbus.h              | 2 --
 4 files changed, 1 insertion(+), 6 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 5a957a9a0984..8ad576ecd0f1 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -370,8 +370,6 @@ static int __init xen_guest_init(void)
 		return -ENOMEM;
 	}
 	gnttab_init();
-	if (!xen_initial_domain())
-		xenbus_probe();
 
 	/*
 	 * Making sure board specific code will not set up ops for
diff --git a/drivers/xen/xenbus/xenbus.h b/drivers/xen/xenbus/xenbus.h
index dc1537335414..2a93b7c9c159 100644
--- a/drivers/xen/xenbus/xenbus.h
+++ b/drivers/xen/xenbus/xenbus.h
@@ -115,7 +115,6 @@ int xenbus_probe_node(struct xen_bus_type *bus,
 		      const char *type,
 		      const char *nodename);
 int xenbus_probe_devices(struct xen_bus_type *bus);
-void xenbus_probe(void);
 
 void xenbus_dev_changed(const char *node, struct xen_bus_type *bus);
 
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 18ffd0551b54..8a75092bb148 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -683,7 +683,7 @@ void unregister_xenstore_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL_GPL(unregister_xenstore_notifier);
 
-void xenbus_probe(void)
+static void xenbus_probe(void)
 {
 	xenstored_ready = 1;
 
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index 2c43b0ef1e4d..bf3cfc7c35d0 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -192,8 +192,6 @@ void xs_suspend_cancel(void);
 
 struct work_struct;
 
-void xenbus_probe(void);
-
 #define XENBUS_IS_ERR_READ(str) ({			\
 	if (!IS_ERR(str) && strlen(str) == 0) {		\
 		kfree(str);				\
-- 
2.17.1