Messages in this thread | | | Date | Fri, 5 Feb 2010 10:30:58 -0500 (EST) | From | Alan Stern <> | Subject | Re: [Patch 0/2] sysfs: fix s_active lockdep warning |
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On Fri, 5 Feb 2010, Peter Zijlstra wrote:
> Right, so this device stuff is much more complicated than I was led to > believe ;-)
Haven't I told you all along that tree-structured locking is complicated? :-)
> So the device core doesn't know, so how are you guys making sure there > really are no deadlocks hidden in there somewhere?
In the code I've seen, deadlocks are avoided by always taking the locks in the same order. But who knows? Maybe there _are_ some hidden deadlocks lurking. For now we can't rely on lockdep to find them, though, because it gets sidetracked by all the false positives.
> > But for now perhaps a compromise is in > > order. We could make the switch from semaphores to mutexes while > > avoiding lockdep issues by assigning the device mutexes to a > > "don't-verify" class. Is there such a thing, or could it be added? > > Something like the below might work, but it should go along with a > checkpatch.pl mod to ensure we don't grow any new users (just don't feel > like brushing up my perl fu enough to actually make sense of that > script)
I'll try it out in the next few days, and if it looks good maybe the checkpatch maintainers can lend some assistance before it gets submitted.
Alan Stern
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