Re: [rtc-linux] [PATCH] rtc: recycle id when unloading a rtc driver

From: Alexander Holler
Date: Wed Dec 19 2012 - 02:56:12 EST

Am 19.12.2012 08:45, schrieb Andrew Morton:
On Wed, 19 Dec 2012 08:37:07 +0100 Alexander Holler <holler@xxxxxxxxxxxxx> wrote:

Am 19.12.2012 01:46, schrieb Andrew Morton:
On Thu, 2 Aug 2012 16:53:25 -0700
Vincent Palatin <vpalatin@xxxxxxxxxxxx> wrote:

When calling rtc_device_unregister, we are not freeing the id used by the
So when doing a unload/load cycle for a RTC driver (e.g. rmmod rtc_cmos
&& modprobe rtc_cmos), its id is incremented by one. As a consequence,
we no longer have neither an rtc0 driver nor a /proc/driver/rtc (as it
only exists for the first driver).

Signed-off-by: Vincent Palatin <vpalatin@xxxxxxxxxxxx>
drivers/rtc/class.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index dc4c274..37b1d82 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -238,6 +238,7 @@ void rtc_device_unregister(struct rtc_device *rtc)
rtc->ops = NULL;
+ ida_simple_remove(&rtc_ida, rtc->id);

Now I think about it, this shouldn't have been needed?

That put_device() should call rtc_device_release(), which does the
ida_simple_remove(). Isn't that working?

It is, see the mini-thread, patch and my comment here:

Maybe it would be better to move the ida_simple_remove from the
rtc_device_release to rt_device_unregister as I've hinted in the above
comment. That would make it easier to spot the ida_simple_remove().

I'm all confused.

Lothar's patch simply reverts Vincent's patch. And that appears to be
the correct thing to so, as the ida_simple_remove() in
rtc_device_release() should be sufficient.

But apparently that doesn't work, because Vincent was seeing the RTC
ID's increment rather than getting reused.

Is it the case that rtc_device_release() is not being called sometimes?
If so, under what circumstances?

Maybe something (sysfs or whatever) still has a reference to it. Vincent should check that.

But I'm sure the ID will be recycled with that put_device() in unregister because I've got the same warning as Lothar did when (porperly) removing an RTC (with kernel 3.7).


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at