Messages in this thread | | | Subject | Re: [PATCH 5/5] hwmon: (sch56xx) Drop watchdog driver data reference count callbacks | From | Guenter Roeck <> | Date | Mon, 21 Dec 2015 05:21:21 -0800 |
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Hi Hans,
On 12/21/2015 02:37 AM, Hans de Goede wrote: > Hi, > > On 20-12-15 22:05, Guenter Roeck wrote: >> Reference counting is now implemented in the watchdog core and no longer >> required in watchdog drivers. >> >> Signed-off-by: Guenter Roeck <linux@roeck-us.net> >> --- >> drivers/hwmon/sch56xx-common.c | 30 ------------------------------ >> 1 file changed, 30 deletions(-) >> >> diff --git a/drivers/hwmon/sch56xx-common.c b/drivers/hwmon/sch56xx-common.c >> index 738681983284..88dba68a9abb 100644 >> --- a/drivers/hwmon/sch56xx-common.c >> +++ b/drivers/hwmon/sch56xx-common.c >> @@ -30,7 +30,6 @@ >> #include <linux/watchdog.h> >> #include <linux/miscdevice.h> >> #include <linux/uaccess.h> >> -#include <linux/kref.h> >> #include <linux/slab.h> >> #include "sch56xx-common.h" >> >> @@ -67,7 +66,6 @@ MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started (default=" >> struct sch56xx_watchdog_data { >> u16 addr; >> struct mutex *io_lock; >> - struct kref kref; >> struct watchdog_info wdinfo; >> struct watchdog_device wddev; >> u8 watchdog_preset; >> @@ -258,15 +256,6 @@ EXPORT_SYMBOL(sch56xx_read_virtual_reg12); >> * Watchdog routines >> */ >> >> -/* Release our data struct when we're unregistered *and* >> - all references to our watchdog device are released */ >> -static void watchdog_release_resources(struct kref *r) >> -{ >> - struct sch56xx_watchdog_data *data = >> - container_of(r, struct sch56xx_watchdog_data, kref); >> - kfree(data); > > You're not replacing this kfree() anywhere, so now the data > allocated by sch56xx_watchdog_register() never gets free-ed > after a sch56xx_watchdog_unregister(). If I read this patch > set correctly then after this patch-set it is safe to > immediately free the memory containing the struct watchdog_device > (and also the struct wdinfo ?) after calling > watchdog_unregister_device(), even if userspace still has the > watchdog cdev open, correct ? > Yes, this is correct for both struct watchdog_device and struct wdinfo.
> In that case (continue reading below) ... > >> -} >> - >> static int watchdog_set_timeout(struct watchdog_device *wddev, >> unsigned int timeout) >> { >> @@ -395,28 +384,12 @@ static int watchdog_stop(struct watchdog_device *wddev) >> return 0; >> } >> >> -static void watchdog_ref(struct watchdog_device *wddev) >> -{ >> - struct sch56xx_watchdog_data *data = watchdog_get_drvdata(wddev); >> - >> - kref_get(&data->kref); >> -} >> - >> -static void watchdog_unref(struct watchdog_device *wddev) >> -{ >> - struct sch56xx_watchdog_data *data = watchdog_get_drvdata(wddev); >> - >> - kref_put(&data->kref, watchdog_release_resources); >> -} >> - >> static const struct watchdog_ops watchdog_ops = { >> .owner = THIS_MODULE, >> .start = watchdog_start, >> .stop = watchdog_stop, >> .ping = watchdog_trigger, >> .set_timeout = watchdog_set_timeout, >> - .ref = watchdog_ref, >> - .unref = watchdog_unref, >> }; >> >> struct sch56xx_watchdog_data *sch56xx_watchdog_register(struct device *parent, >> @@ -448,7 +421,6 @@ struct sch56xx_watchdog_data *sch56xx_watchdog_register(struct device *parent, >> >> data->addr = addr; >> data->io_lock = io_lock; >> - kref_init(&data->kref); >> >> strlcpy(data->wdinfo.identity, "sch56xx watchdog", >> sizeof(data->wdinfo.identity)); >> @@ -494,8 +466,6 @@ EXPORT_SYMBOL(sch56xx_watchdog_register); >> void sch56xx_watchdog_unregister(struct sch56xx_watchdog_data *data) >> { >> watchdog_unregister_device(&data->wddev); >> - kref_put(&data->kref, watchdog_release_resources); >> - /* Don't touch data after this it may have been free-ed! */ > > These 2 lines need to be replaced by a "kfree(data);" rather then being > removed. > Good catch. Fixed.
>> } >> EXPORT_SYMBOL(sch56xx_watchdog_unregister); >> >> > > Regards, > > Hans > > > p.s. > > The patches for da9052_wdt and da9055_wdt are also interesting, > their da905#_wdt_release_resources() functions are nops, > making the entire refcounting exercise a nop. > > For da9052_wdt is the case since this commit: > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/watchdog/da9052_wdt.c?id=0360dffedd7bad92f174b2ce5e69e960451d2b59
And for da9055 with commit ee8c94adff9b ("watchdog: da9055: Fix invalid free of devm_ allocated data").
> > Which fixes the bug it tries to fix in the wrong way, the right > way would have been to change the devm_kzalloc to a regular kzalloc, > since devm_*alloc cannot be used together with refcounting to keep > memory alive after device unregister time. > > What this means is that these drivers actually have a bug wrt > freeing in use memory on driver unbind while userspace has > the watchdog cdev open, and this gets fixed by this patch-set, > it would be very good to mention this in the commit messages.
Good point. I updated the commit log.
Thanks, Guenter
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