linux-kernel - [PATCH 11/68] ALPHA: srmcons, fix racy singleton structure

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Date:	Mon,  5 Mar 2012 14:51:58 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	gregkh@...uxfoundation.org
Cc:	alan@...ux.intel.com, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, jirislaby@...il.com,
	Richard Henderson <rth@...ddle.net>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Matt Turner <mattst88@...il.com>
Subject: [PATCH 11/68] ALPHA: srmcons, fix racy singleton structure

The test and the assignment were racy. Make it really a singleton.
This is achieved by one global variable initialized at the module
init.

Signed-off-by: Jiri Slaby <jslaby@...e.cz>
Cc: Richard Henderson <rth@...ddle.net>
Cc: Ivan Kokshaysky <ink@...assic.park.msu.ru>
Cc: Matt Turner <mattst88@...il.com>
---
 arch/alpha/kernel/srmcons.c |   40 +++++-----------------------------------
 1 file changed, 5 insertions(+), 35 deletions(-)

diff --git a/arch/alpha/kernel/srmcons.c b/arch/alpha/kernel/srmcons.c
index f1fdf17..2c89ce5c 100644
--- a/arch/alpha/kernel/srmcons.c
+++ b/arch/alpha/kernel/srmcons.c
@@ -33,7 +33,7 @@ struct srmcons_private {
 	struct tty_struct *tty;
 	struct timer_list timer;
 	spinlock_t lock;
-};
+} srmcons_singleton;
 
 typedef union _srmcons_result {
 	struct {
@@ -154,43 +154,10 @@ srmcons_chars_in_buffer(struct tty_struct *tty)
 }
 
 static int
-srmcons_get_private_struct(struct srmcons_private **ps)
-{
-	static struct srmcons_private *srmconsp = NULL;
-	static DEFINE_SPINLOCK(srmconsp_lock);
-	unsigned long flags;
-	int retval = 0;
-
-	if (srmconsp == NULL) {
-		srmconsp = kmalloc(sizeof(*srmconsp), GFP_KERNEL);
-		spin_lock_irqsave(&srmconsp_lock, flags);
-
-		if (srmconsp == NULL)
-			retval = -ENOMEM;
-		else {
-			srmconsp->tty = NULL;
-			spin_lock_init(&srmconsp->lock);
-			setup_timer(&srmconsp->timer, srmcons_receive_chars,
-					(unsigned long)srmconsp);
-		}
-
-		spin_unlock_irqrestore(&srmconsp_lock, flags);
-	}
-
-	*ps = srmconsp;
-	return retval;
-}
-
-static int
 srmcons_open(struct tty_struct *tty, struct file *filp)
 {
-	struct srmcons_private *srmconsp;
+	struct srmcons_private *srmconsp = &srmcons_singleton;
 	unsigned long flags;
-	int retval;
-
-	retval = srmcons_get_private_struct(&srmconsp);
-	if (retval)
-		return retval;
 
 	spin_lock_irqsave(&srmconsp->lock, flags);
 
@@ -236,6 +203,9 @@ static const struct tty_operations srmcons_ops = {
 static int __init
 srmcons_init(void)
 {
+	spin_lock_init(&srmcons_singleton.lock);
+	setup_timer(&srmcons_singleton.timer, srmcons_receive_chars,
+			(unsigned long)&srmcons_singleton);
 	if (srm_is_registered_console) {
 		struct tty_driver *driver;
 		int err;
-- 
1.7.9.2


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