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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2008-08-11 03:30:24 -0400
committerIngo Molnar <mingo@elte.hu>2008-08-11 03:30:24 -0400
commit7531e2f34d1d551b096143f19111139f0dd84c8b (patch)
tree0a29d6703e28dc6752b9b4085594cca238595aac /include/linux/rcuclassic.h
parent4f3e7524b2e703d9f8b02ac338153a53dd7ede66 (diff)
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 <n> locks might as well do <n+1>, 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 <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'include/linux/rcuclassic.h')
-rw-r--r--include/linux/rcuclassic.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h
index 8c774905dcfe..4ab843622727 100644
--- a/include/linux/rcuclassic.h
+++ b/include/linux/rcuclassic.h
@@ -117,7 +117,7 @@ extern int rcu_needs_cpu(int cpu);
117#ifdef CONFIG_DEBUG_LOCK_ALLOC 117#ifdef CONFIG_DEBUG_LOCK_ALLOC
118extern struct lockdep_map rcu_lock_map; 118extern struct lockdep_map rcu_lock_map;
119# define rcu_read_acquire() \ 119# define rcu_read_acquire() \
120 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, _THIS_IP_) 120 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
121# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) 121# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
122#else 122#else
123# define rcu_read_acquire() do { } while (0) 123# define rcu_read_acquire() do { } while (0)