linux-kernel - [PATCH v3 2/3] hvc_init(): Enforce one-time initialization.

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Date:	Tue, 08 Nov 2011 13:45:04 -0800
From:	Miche Baker-Harvey <miche@...gle.com>
To:	Greg Kroah-Hartman <gregkh@...e.de>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	xen-devel@...ts.xensource.com,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Anton Blanchard <anton@...ba.org>,
	Amit Shah <amit.shah@...hat.com>,
	Mike Waychison <mikew@...gle.com>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	Eric Northrup <digitaleric@...gle.com>
Subject: [PATCH v3 2/3] hvc_init():  Enforce one-time initialization.

hvc_init() must only be called once, and no thread should continue with hvc_alloc()
until after initialization is complete.  The original code does not enforce either
of these requirements.  A new mutex limits entry to hvc_init() to a single thread,
and blocks all later comers until it has completed.

This patch fixes multiple crash symptoms.

Signed-off-by: Miche Baker-Harvey <miche@...gle.com>
---
 drivers/tty/hvc/hvc_console.c |   13 +++++++++++--
 1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index b6b2d18..09a6159 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -29,8 +29,9 @@
 #include <linux/kernel.h>
 #include <linux/kthread.h>
 #include <linux/list.h>
-#include <linux/module.h>
 #include <linux/major.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/sysrq.h>
 #include <linux/tty.h>
 #include <linux/tty_flip.h>
@@ -84,6 +85,10 @@ static LIST_HEAD(hvc_structs);
  * list traversal.
  */
 static DEFINE_SPINLOCK(hvc_structs_lock);
+/*
+ * only one task does allocation at a time.
+ */
+static DEFINE_MUTEX(hvc_ports_mutex);
 
 /*
  * This value is used to assign a tty->index value to a hvc_struct based
@@ -825,11 +830,15 @@ struct hvc_struct *hvc_alloc(uint32_t vtermno, int data,
 	int i;
 
 	/* We wait until a driver actually comes along */
+	mutex_lock(&hvc_ports_mutex);
 	if (!hvc_driver) {
 		int err = hvc_init();
-		if (err)
+		if (err) {
+			mutex_unlock(&hvc_ports_mutex);
 			return ERR_PTR(err);
+		}
 	}
+	mutex_unlock(&hvc_ports_mutex);
 
 	hp = kzalloc(ALIGN(sizeof(*hp), sizeof(long)) + outbuf_size,
 			GFP_KERNEL);

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