linux-kernel - [PATCH v2 1/2] watchdog: dw

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <1431059265-9204-1-git-send-email-dianders@chromium.org>
Date:	Thu,  7 May 2015 21:27:44 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	wim@...ana.be, linux@...ck-us.net
Cc:	jszhang@...vell.com, Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Doug Anderson <dianders@...omium.org>,
	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/2] watchdog: dw_wdt: No need for a spinlock

Right now the dw_wdt uses a spinlock to protect dw_wdt_open().  The
problem is that while holding the spinlock we call:
-> dw_wdt_set_top()
   -> dw_wdt_top_in_seconds()
      -> clk_get_rate()
         -> clk_prepare_lock()
            -> mutex_lock()

Locking a mutex while holding a spinlock is not allowed and leads to
warnings like "BUG: spinlock wrong CPU on CPU#1", among other
problems.

There's no reason to use a spinlock.  Only dw_wdt_open() was protected
and the test_and_set_bit() at the start of that function protects us
anyway.

Signed-off-by: Doug Anderson <dianders@...omium.org>
---
Changes in v2:
- Don't switch to mutex; just don't use spinlock at all as per Dmitry

 drivers/watchdog/dw_wdt.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
index d0bb949..a284abd 100644
--- a/drivers/watchdog/dw_wdt.c
+++ b/drivers/watchdog/dw_wdt.c
@@ -35,7 +35,6 @@
 #include <linux/pm.h>
 #include <linux/platform_device.h>
 #include <linux/reboot.h>
-#include <linux/spinlock.h>
 #include <linux/timer.h>
 #include <linux/uaccess.h>
 #include <linux/watchdog.h>
@@ -61,7 +60,6 @@ MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started "
 #define WDT_TIMEOUT		(HZ / 2)
 
 static struct {
-	spinlock_t		lock;
 	void __iomem		*regs;
 	struct clk		*clk;
 	unsigned long		in_use;
@@ -177,7 +175,6 @@ static int dw_wdt_open(struct inode *inode, struct file *filp)
 	/* Make sure we don't get unloaded. */
 	__module_get(THIS_MODULE);
 
-	spin_lock(&dw_wdt.lock);
 	if (!dw_wdt_is_enabled()) {
 		/*
 		 * The watchdog is not currently enabled. Set the timeout to
@@ -190,8 +187,6 @@ static int dw_wdt_open(struct inode *inode, struct file *filp)
 
 	dw_wdt_set_next_heartbeat();
 
-	spin_unlock(&dw_wdt.lock);
-
 	return nonseekable_open(inode, filp);
 }
 
@@ -348,8 +343,6 @@ static int dw_wdt_drv_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	spin_lock_init(&dw_wdt.lock);
-
 	ret = misc_register(&dw_wdt_miscdev);
 	if (ret)
 		goto out_disable_clk;
-- 
2.2.0.rc0.207.ga3a616c

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/