On Fri, 7 Aug 2009, Peter Zijlstra wrote: > On Fri, 2009-08-07 at 09:46 -0500, Clark Williams wrote: > > Peter, > > > > I'm getting this warning from lockdep when booting on my T60. > > > > The two addresses reported (0xffffffff812664a2 and 0xffffffff812664ae) > > actually bracket one call to mutex_lock() in driver_attach() so I'm not > > sure what the complaint is. > Oh, that's tglx who's gone wild with sem->mutex conversions. Is this code available somewhere? > It used to be that _all_ dev->sem instances were taken on suspend or > something like that, I think that got fixed a long while back. > > I'd have to look at what the current locking requirements for dev->sem > are. It is supposed to be locked whenever the driver core invokes a probe, remove, or PM-related callback. Under some circumstances, the parent's semaphore is supposed to be locked as well. Individual subsystems may have their own requirements in addition to these. The ordering requirement is: Don't try to acquire a device's lock if you already hold the lock for a non-ancestor device. More generally (if more obscurely): If you already hold device A's lock, then don't try to acquire the lock for device B unless you already hold the lock for A & B's most recent common ancestor. > I remember talking to Alan on several occasions about this, and I just > went over some of the old emails, but I must say the precise > requirements stay hidden from me. Also, I'm not sure these emails are > still representative of the current state. I think they are, pretty much. The real problem, of course, is that lockdep doesn't understand tree-structured lock orderings. Hence it isn't practical to convert dev->sem into a mutex. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
