[PATCH v2 1/2] watchdog: dw_wdt: No need for a spinlock

Doug Anderson
2015-05-08T04:28:00Z

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@chromium.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