On Sat, 2007-10-27 at 08:47 -0700, Arjan van de Ven wrote:
> On Sat, 27 Oct 2007 17:12:41 +0200 (CEST)
> Jiri Kosina <[email protected]> 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.
Right, the fd could be transferred using unix sockets or fork(). That
would indeed seriously break a mutex.
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