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.
> 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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