Messages in this thread Patch in this message | | | Subject | Re: [Patch 0/2] sysfs: fix s_active lockdep warning | From | Peter Zijlstra <> | Date | Fri, 05 Feb 2010 11:18:37 +0100 |
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On Thu, 2010-02-04 at 13:37 -0500, Alan Stern wrote: > On Thu, 4 Feb 2010, Peter Zijlstra wrote: > > > > This doesn't address the fact that we really have multiple device trees > > > (for example, class devices are handled separately from normal > > > devices). With the above patch installed, I still get lockdep > > > violations farther on during boot: > > > > <snip lockdep splat> > > > > Hmm, so you have multiple interacting trees? I had understood you only > > had a single device tree. > > The real situation is kind of complicated, and I'm not familiar with > all the details. But it's certainly true that a driver will want to > work with (and lock!) multiple struct device's that don't have a > parent-child relation in the tree. The simplest example is regular > devices together with class devices, and another might be PCI devices > together with their "shadow" ACPI devices. > > > So how many trees are there, is that fixed? > > Does the device know what tree it is going to end up in? > > The driver generally knows, but AFAIK that information is not passed > back to the driver core. At least, not directly -- you might say that > it could be deduced from the parent pointer, assuming the core already > knows all about the parent. > > > If yes, then you can extend the setup_mutex_depth() function to pick a > > different class stack for each tree. > > Maybe this could be done.
Right, so this device stuff is much more complicated than I was led to believe ;-)
So the device core doesn't know, so how are you guys making sure there really are no deadlocks hidden in there somewhere?
> 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)
--- include/linux/lockdep.h | 2 ++ kernel/lockdep.c | 5 +++++ 2 files changed, 7 insertions(+), 0 deletions(-)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index 9ccf0e2..4e30ab4 100644 --- a/include/linux/lockdep.h +++ b/include/linux/lockdep.h @@ -40,6 +40,8 @@ struct lock_class_key { struct lockdep_subclass_key subkeys[MAX_LOCKDEP_SUBCLASSES]; }; +extern struct lock_class_key __lockdep_no_validate__; + #define LOCKSTAT_POINTS 4 /* diff --git a/kernel/lockdep.c b/kernel/lockdep.c index c62ec14..af65a34 100644 --- a/kernel/lockdep.c +++ b/kernel/lockdep.c @@ -2716,6 +2716,8 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name, } EXPORT_SYMBOL_GPL(lockdep_init_map); +struct lock_class_key __lockdep_no_validate__; + /* * This gets called for every mutex_lock*()/spin_lock*() operation. * We maintain the dependency maps and validate the locking attempt: @@ -2750,6 +2752,9 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, return 0; } + if (lock->key == &__lockdep_no_validate__) + check = 1; + if (!subclass) class = lock->class_cache; /*
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