Messages in this thread | | | Subject | Re: BUG: lock held when returning to user space | From | Peter Zijlstra <> | Date | Sat, 27 Oct 2007 17:28:41 +0200 |
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On Sat, 2007-10-27 at 17:12 +0200, Jiri Kosina 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. > > Peter, what is the preferred way to annotate these kinds of locking for > lockdep to express that it is intended?
Not sure, I'd not thought that anyone would actually want to do this. I'm also not sure how I stand on this, I'd prefer to say: don't do this!
I think, in this case, the lock is associated with a kernel object that is properly cleaned up if the holding tasks gets a SIGKILL. But in general I'd like to see this kind of thing go away.
Now I could probably come up with an annotation to hide it, but what do other people think, Ingo, Linus, Andrew, do we want to keep kernel locks held over userspace?
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