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Message-ID: <20151207161549.GA6030@localhost>
Date: Mon, 7 Dec 2015 11:15:49 -0500
From: Damien Riegel <damien.riegel@...oirfairelinux.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Wim Van Sebroeck <wim@...ana.be>, linux-watchdog@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC/RFT PATCH] watchdog: Move watchdog device creation to
watchdog_dev.c
On Sun, Dec 06, 2015 at 11:51:41AM -0800, Guenter Roeck wrote:
> The watchdog character device s currently created in watchdog_dev.c,
> and the watchdog device in watchdog_core.c. This results in
> cross-dependencies, as the device creation needs to know the watchdog
> character device number.
>
> On top of that, the watchdog character device is created before the
> watchdog device is created. This can result in race conditions if the
> watchdog device node is accessed before the watchdog device has been
> created.
>
> To solve the problem, move watchdog device creation into watchdog_dev.c,
> and create the watchdog device prior to creating its device node.
> Also move device class creation into watchdog_dev.c, since this is now
> the only place where the watchdog class is needed.
>
> Inspired by an earlier patch set from Damien Riegel.
>
> Cc: Damien Riegel <damien.riegel@...oirfairelinux.com>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
> Hi Damien,
>
> I think this approach would be a bit better. The watchdog device isn't
> really used in the watchdog core code, so it is better created in
> watchdog_dev.c. That also fits well with other pending changes, such as
> sysfs attribute support, and my attempts to move the ref/unref functions
> completely into the watchdog core. As a side effect, it also cleans up
> the error path in __watchdog_register_device().
>
> What do you think ?
Hi Guenter,
Like the idea, but I don't really get the separation. For instance, you
move watchdog_class in watchdog_dev.c but you keep watchdog_ida in
watchdog_core.c whereas it is only used for device creation/deletion.
Also a few minor comments below.
> The code has been compile tested only so far. I'll try to test it later
> today, but I wanted to get it out for discussion.
I'll give it a try but I have only one board to test it.
>
> Thanks,
> Guenter
>
> drivers/watchdog/watchdog_core.c | 37 ++----------------------
> drivers/watchdog/watchdog_core.h | 2 +-
> drivers/watchdog/watchdog_dev.c | 61 ++++++++++++++++++++++++++++++++--------
> 3 files changed, 54 insertions(+), 46 deletions(-)
>
> diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
> index 873f13972cf4..089e930fce19 100644
> --- a/drivers/watchdog/watchdog_core.c
> +++ b/drivers/watchdog/watchdog_core.c
> @@ -41,7 +41,6 @@
> #include "watchdog_core.h" /* For watchdog_dev_register/... */
>
> static DEFINE_IDA(watchdog_ida);
> -static struct class *watchdog_class;
>
> /*
> * Deferred Registration infrastructure.
> @@ -139,7 +138,7 @@ EXPORT_SYMBOL_GPL(watchdog_init_timeout);
>
> static int __watchdog_register_device(struct watchdog_device *wdd)
> {
> - int ret, id = -1, devno;
> + int ret, id = -1;
>
> if (wdd == NULL || wdd->info == NULL || wdd->ops == NULL)
> return -EINVAL;
> @@ -192,16 +191,6 @@ static int __watchdog_register_device(struct watchdog_device *wdd)
> }
> }
>
> - devno = wdd->cdev.dev;
> - wdd->dev = device_create(watchdog_class, wdd->parent, devno,
> - NULL, "watchdog%d", wdd->id);
> - if (IS_ERR(wdd->dev)) {
> - watchdog_dev_unregister(wdd);
> - ida_simple_remove(&watchdog_ida, id);
> - ret = PTR_ERR(wdd->dev);
> - return ret;
> - }
> -
> return 0;
> }
>
> @@ -232,19 +221,8 @@ EXPORT_SYMBOL_GPL(watchdog_register_device);
>
> static void __watchdog_unregister_device(struct watchdog_device *wdd)
> {
> - int ret;
> - int devno;
> -
> - if (wdd == NULL)
> - return;
> -
> - devno = wdd->cdev.dev;
> - ret = watchdog_dev_unregister(wdd);
> - if (ret)
> - pr_err("error unregistering /dev/watchdog (err=%d)\n", ret);
> - device_destroy(watchdog_class, devno);
> + watchdog_dev_unregister(wdd);
> ida_simple_remove(&watchdog_ida, wdd->id);
> - wdd->dev = NULL;
> }
>
> /**
> @@ -287,17 +265,9 @@ static int __init watchdog_init(void)
> {
> int err;
>
> - watchdog_class = class_create(THIS_MODULE, "watchdog");
> - if (IS_ERR(watchdog_class)) {
> - pr_err("couldn't create class\n");
> - return PTR_ERR(watchdog_class);
> - }
> -
> err = watchdog_dev_init();
> - if (err < 0) {
> - class_destroy(watchdog_class);
> + if (err < 0)
> return err;
> - }
>
> watchdog_deferred_registration();
> return 0;
> @@ -306,7 +276,6 @@ static int __init watchdog_init(void)
> static void __exit watchdog_exit(void)
> {
> watchdog_dev_exit();
> - class_destroy(watchdog_class);
> ida_destroy(&watchdog_ida);
> }
>
> diff --git a/drivers/watchdog/watchdog_core.h b/drivers/watchdog/watchdog_core.h
> index 6c951418fca7..86ff962d1e15 100644
> --- a/drivers/watchdog/watchdog_core.h
> +++ b/drivers/watchdog/watchdog_core.h
> @@ -32,6 +32,6 @@
> * Functions/procedures to be called by the core
> */
> extern int watchdog_dev_register(struct watchdog_device *);
> -extern int watchdog_dev_unregister(struct watchdog_device *);
> +extern void watchdog_dev_unregister(struct watchdog_device *);
> extern int __init watchdog_dev_init(void);
> extern void __exit watchdog_dev_exit(void);
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 56a649e66eb2..07abe8c9e58c 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -49,6 +49,9 @@ static dev_t watchdog_devt;
> /* the watchdog device behind /dev/watchdog */
> static struct watchdog_device *old_wdd;
>
> +/* the watchdog device class */
> +static struct class *watchdog_class;
> +
> /*
> * watchdog_ping: ping the watchdog.
> * @wdd: the watchdog device to ping
> @@ -523,7 +526,7 @@ static struct miscdevice watchdog_miscdev = {
> * thus we set it up like that.
> */
>
> -int watchdog_dev_register(struct watchdog_device *wdd)
> +int _watchdog_dev_register(struct watchdog_device *wdd)
Doc not updated and still refers to watchdog_dev_register.
> {
> int err, devno;
>
> @@ -532,11 +535,12 @@ int watchdog_dev_register(struct watchdog_device *wdd)
> watchdog_miscdev.parent = wdd->parent;
> err = misc_register(&watchdog_miscdev);
> if (err != 0) {
> - pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n",
> - wdd->info->identity, WATCHDOG_MINOR, err);
> + dev_err(wdd->dev,
> + "Cannot register miscdev on minor=%d (err=%d).\n",
> + WATCHDOG_MINOR, err);
> if (err == -EBUSY)
> - pr_err("%s: a legacy watchdog module is probably present.\n",
> - wdd->info->identity);
> + dev_err(wdd->dev,
> + "A legacy watchdog module is probably present.\n");
> old_wdd = NULL;
> return err;
> }
> @@ -550,8 +554,8 @@ int watchdog_dev_register(struct watchdog_device *wdd)
> /* Add the device */
> err = cdev_add(&wdd->cdev, devno, 1);
> if (err) {
> - pr_err("watchdog%d unable to add device %d:%d\n",
> - wdd->id, MAJOR(watchdog_devt), wdd->id);
> + dev_err(wdd->dev, "Unable to add device %d:%d\n",
> + MAJOR(watchdog_devt), wdd->id);
> if (wdd->id == 0) {
> misc_deregister(&watchdog_miscdev);
> old_wdd = NULL;
> @@ -567,7 +571,7 @@ int watchdog_dev_register(struct watchdog_device *wdd)
> * Unregister the watchdog and if needed the legacy /dev/watchdog device.
> */
>
> -int watchdog_dev_unregister(struct watchdog_device *wdd)
> +void _watchdog_dev_unregister(struct watchdog_device *wdd)
Doc not updated.
> {
> mutex_lock(&wdd->lock);
> set_bit(WDOG_UNREGISTERED, &wdd->status);
> @@ -578,7 +582,31 @@ int watchdog_dev_unregister(struct watchdog_device *wdd)
> misc_deregister(&watchdog_miscdev);
> old_wdd = NULL;
> }
> - return 0;
> +}
> +
> +int watchdog_dev_register(struct watchdog_device *wdd)
> +{
> + dev_t devno;
> + int ret;
> +
> + devno = MKDEV(MAJOR(watchdog_devt), wdd->id);
This is now done twice, here and in _watchdog_dev_register. Maybe
_watchdog_dev_register should be updated to read:
devno = wdd->dev.devt
The end result is the same but the link between the two devices is more
explicit (like it is now).
> + wdd->dev = device_create(watchdog_class, wdd->parent, devno,
> + wdd, "watchdog%d", wdd->id);
> + if (IS_ERR(wdd->dev))
> + return PTR_ERR(wdd->dev);
> +
> + ret = _watchdog_dev_register(wdd);
> + if (ret)
> + device_destroy(watchdog_class, devno);
> +
> + return ret;
> +}
> +
> +void watchdog_dev_unregister(struct watchdog_device *wdd)
> +{
> + _watchdog_dev_unregister(wdd);
> + device_destroy(watchdog_class, wdd->dev->devt);
> + wdd->dev = NULL;
> }
>
> /*
> @@ -589,9 +617,19 @@ int watchdog_dev_unregister(struct watchdog_device *wdd)
>
> int __init watchdog_dev_init(void)
> {
> - int err = alloc_chrdev_region(&watchdog_devt, 0, MAX_DOGS, "watchdog");
> - if (err < 0)
> + int err;
> +
> + watchdog_class = class_create(THIS_MODULE, "watchdog");
> + if (IS_ERR(watchdog_class)) {
> + pr_err("couldn't create watchdog class\n");
> + return PTR_ERR(watchdog_class);
> + }
> +
> + err = alloc_chrdev_region(&watchdog_devt, 0, MAX_DOGS, "watchdog");
> + if (err < 0) {
> pr_err("watchdog: unable to allocate char dev region\n");
> + class_destroy(watchdog_class);
> + }
Newline here ? checkpatch does not complain and this file style is not
consistent on new line before return. Don't know which style is
preferred.
> return err;
> }
>
> @@ -604,4 +642,5 @@ int __init watchdog_dev_init(void)
> void __exit watchdog_dev_exit(void)
> {
> unregister_chrdev_region(watchdog_devt, MAX_DOGS);
> + class_destroy(watchdog_class);
> }
> --
> 2.1.4
>
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