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Message-ID: <20110223204350.GA7433@infomag.iguana.be>
Date: Wed, 23 Feb 2011 21:43:51 +0100
From: Wim Van Sebroeck <wim@...ana.be>
To: LKML <linux-kernel@...r.kernel.org>,
Linux Watchdog Mailing List <linux-watchdog@...r.kernel.org>
Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: [RFC] [PATCH 6/10] Generic Watchdog Timer Driver
commit afe3de93859443b575407f39a2e655956c02e088
Author: Wim Van Sebroeck <wim@...ana.be>
Date: Sun Jul 18 10:39:00 2010 +0000
watchdog: WatchDog Timer Driver Core - Part 6
Since we don't want that a driver module can be removed
while the watchdog timer is still active, we lock the
driver module (by incremeting the reference counter).
After a clean close of the watchdog driver we unlock the
driver module.
If /dev/watchdog is closed uncleanly (and the watchdog is
still active) then we do not unlock the driver module,
but keep it, so that next time /dev/watchdog get's opened
we can continue triggering the watchdog.
Signed-off-by: Alan Cox <alan@...rguk.ukuu.org.uk>
Signed-off-by: Wim Van Sebroeck <wim@...ana.be>
diff --git a/Documentation/watchdog/src/watchdog-with-timer-example.c b/Documentation/watchdog/src/watchdog-with-timer-example.c
index f1d4f217..604fd91 100644
--- a/Documentation/watchdog/src/watchdog-with-timer-example.c
+++ b/Documentation/watchdog/src/watchdog-with-timer-example.c
@@ -127,6 +127,7 @@ static const struct watchdog_info wdt_info = {
};
static const struct watchdog_ops wdt_ops = {
+ .owner = THIS_MODULE,
.start = wdt_start,
.stop = wdt_stop,
.ping = wdt_ping,
diff --git a/Documentation/watchdog/watchdog-kernel-api.txt b/Documentation/watchdog/watchdog-kernel-api.txt
index f15e8d4..472bfea 100644
--- a/Documentation/watchdog/watchdog-kernel-api.txt
+++ b/Documentation/watchdog/watchdog-kernel-api.txt
@@ -63,6 +63,7 @@ It contains following fields:
The list of watchdog operations is defined as:
struct watchdog_ops {
+ struct module *owner;
/* mandatory operations */
int (*start)(struct watchdog_device *);
int (*stop)(struct watchdog_device *);
@@ -72,6 +73,10 @@ struct watchdog_ops {
int (*set_timeout)(struct watchdog_device *, int);
};
+It is important that you first define the module owner of the watchdog timer
+driver's operations. This module owner will be used to lock the module when
+the watchdog is active. (You don't want to unload the module when you're
+watchdog timer device is still active).
Some operations are mandatory and some are optional. The mandatory operations
are:
* start: this is a pointer to the routine that starts the watchdog timer
@@ -121,3 +126,8 @@ bit-operations. The status bit's that are defined are:
* WDOG_DEV_OPEN: this status bit shows whether or not the watchdog device
was opened via /dev/watchdog.
(This bit should only be used by the WatchDog Timer Driver Core).
+* WDOG_ORPHAN: when /dev/watchdog was closed, but the watchdog is still active
+ then we don't unload the module. This bit is set when this situation occurs.
+ When re-opening /dev/watchdog before a reboot occurs, you can then still use
+ and ping the watchdog timer device.
+ (This bit should only be used by the WatchDog Timer Driver Core).
diff --git a/drivers/watchdog/core/watchdog_core.c b/drivers/watchdog/core/watchdog_core.c
index 52bc520..d1a824e 100644
--- a/drivers/watchdog/core/watchdog_core.c
+++ b/drivers/watchdog/core/watchdog_core.c
@@ -60,6 +60,10 @@ int register_watchdogdevice(struct watchdog_device *wdd)
if (wdd == NULL || wdd->info == NULL || wdd->ops == NULL)
return -ENODATA;
+ /* Make sure that the owner of the watchdog operations exists */
+ if (wdd->ops->owner == NULL)
+ return -ENODATA;
+
/* Make sure that the mandatory operations are supported */
if (wdd->ops->start == NULL || wdd->ops->stop == NULL)
return -ENODATA;
diff --git a/drivers/watchdog/core/watchdog_dev.c b/drivers/watchdog/core/watchdog_dev.c
index b80c6e6..d3dfac2 100644
--- a/drivers/watchdog/core/watchdog_dev.c
+++ b/drivers/watchdog/core/watchdog_dev.c
@@ -259,7 +259,7 @@ static long watchdog_ioctl(struct file *file, unsigned int cmd,
static int watchdog_open(struct inode *inode, struct file *file)
{
- int err;
+ int err = -EBUSY;
trace("%p, %p", inode, file);
@@ -267,14 +267,26 @@ static int watchdog_open(struct inode *inode, struct file *file)
if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status))
return -EBUSY;
+ /* if the /dev/watchdog device is open, we don't want the module
+ * to be unloaded. */
+ if (!try_module_get(wdd->ops->owner))
+ goto out;
+
/* start the watchdog */
err = watchdog_start(wdd);
if (err < 0)
- goto out;
+ goto out_mod;
+
+ /* We leaked a reference to lock the module in on close
+ * now we can reclaim it as we re-opened before triggering */
+ if (test_and_clear_bit(WDOG_ORPHAN, &wdd->status))
+ module_put(wdd->ops->owner);
/* dev/watchdog is a virtual (and thus non-seekable) filesystem */
return nonseekable_open(inode, file);
+out_mod:
+ module_put(wdd->ops->owner);
out:
clear_bit(WDOG_DEV_OPEN, &wdd->status);
return err;
@@ -296,8 +308,13 @@ static int watchdog_release(struct inode *inode, struct file *file)
/* stop the watchdog */
err = watchdog_stop(wdd);
- if (err < 0) {
+
+ /* If the watchdog stopped correctly we let the module unload again */
+ if (err == 0)
+ module_put(wdd->ops->owner);
+ else { /* If not we deliberately leak a module reference */
printk(KERN_CRIT "%s: not stopping watchdog!\n", wdd->name);
+ set_bit(WDOG_ORPHAN, &wdd->status);
watchdog_ping(wdd);
}
diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
index e35f51f..ba08f38 100644
--- a/include/linux/watchdog.h
+++ b/include/linux/watchdog.h
@@ -64,6 +64,7 @@ struct watchdog_device;
/* The watchdog-devices operations */
struct watchdog_ops {
+ struct module *owner;
/* mandatory operations */
int (*start)(struct watchdog_device *);
int (*stop)(struct watchdog_device *);
@@ -84,6 +85,8 @@ struct watchdog_device {
#define WDOG_ACTIVE 0 /* is the watchdog running/active */
#define WDOG_DEV_OPEN 1 /* is the watchdog opened via
* /dev/watchdog */
+#define WDOG_ORPHAN 2 /* is the device module still loaded
+ * after closing /dev/watchdog */
};
/* drivers/watchdog/core/watchdog_core.c */
--
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