Messages in this thread | | | Date | Sat, 27 Oct 2007 08:47:13 -0700 | From | Arjan van de Ven <> | Subject | Re: BUG: lock held when returning to user space |
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On Sat, 27 Oct 2007 17:12:41 +0200 (CEST) Jiri Kosina <jikos@jikos.cz> wrote:
> On Sat, 27 Oct 2007, Gabriel C wrote: > > > I found that today in dmesg after booting current git ( > > ec3b67c11df42362ccda81261d62829042f223f0 ) : > > ... > > [ 592.752777] > > [ 592.752781] ================================================ > > [ 592.753478] [ BUG: lock held when returning to user space! ] > > [ 592.753880] ------------------------------------------------ > > [ 592.754262] hwclock/1452 is leaving the kernel with locks still > > held! [ 592.754655] 1 lock held by hwclock/1452: > > [ 592.755007] #0: (&rtc->char_lock){--..}, at: [<c02a7ebb>] > > rtc_dev_open+0x2e/0x7e > > Yes, this is because rtc keeps a char_lock mutex locked as long as > the device is open, to avoid concurrent accessess. > > It could be easily substituted by some counting -- setting and > clearing bit in struct rtc_device instead of using char_lock, but > doing this just to shut the lockdep off is questionable imho.
it's not about lockdep; what this code doing is not valid use of a mutex: A mutex is required to have a clear process as owner, and in this case it doesn't have that... at all. This is a violation of the kernel mutex semantics.. and should be fixed.
> Peter, what is the preferred way to annotate these kinds of locking > for lockdep to express that it is intended?
the preferred method is to not use a mutex like this...
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