From 7531e2f34d1d551b096143f19111139f0dd84c8b Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 11 Aug 2008 09:30:24 +0200 Subject: lockdep: lock protection locks On Fri, 2008-08-01 at 16:26 -0700, Linus Torvalds wrote: > On Fri, 1 Aug 2008, David Miller wrote: > > > > Taking more than a few locks of the same class at once is bad > > news and it's better to find an alternative method. > > It's not always wrong. > > If you can guarantee that anybody that takes more than one lock of a > particular class will always take a single top-level lock _first_, then > that's all good. You can obviously screw up and take the same lock _twice_ > (which will deadlock), but at least you cannot get into ABBA situations. > > So maybe the right thing to do is to just teach lockdep about "lock > protection locks". That would have solved the multi-queue issues for > networking too - all the actual network drivers would still have taken > just their single queue lock, but the one case that needs to take all of > them would have taken a separate top-level lock first. > > Never mind that the multi-queue locks were always taken in the same order: > it's never wrong to just have some top-level serialization, and anybody > who needs to take locks might as well do , because they sure as > hell aren't going to be on _any_ fastpaths. > > So the simplest solution really sounds like just teaching lockdep about > that one special case. It's not "nesting" exactly, although it's obviously > related to it. Do as Linus suggested. The lock protection lock is called nest_lock. Note that we still have the MAX_LOCK_DEPTH (48) limit to consider, so anything that spills that it still up shit creek. Signed-off-by: Peter Zijlstra Signed-off-by: Ingo Molnar --- include/linux/rcuclassic.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux/rcuclassic.h') diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h index 8c774905dcf..4ab84362272 100644 --- a/include/linux/rcuclassic.h +++ b/include/linux/rcuclassic.h @@ -117,7 +117,7 @@ extern int rcu_needs_cpu(int cpu); #ifdef CONFIG_DEBUG_LOCK_ALLOC extern struct lockdep_map rcu_lock_map; # define rcu_read_acquire() \ - lock_acquire(&rcu_lock_map, 0, 0, 2, 1, _THIS_IP_) + lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) #else # define rcu_read_acquire() do { } while (0) -- cgit v1.2.3-70-g09d2