Messages in this thread | | | Date | Mon, 4 Apr 2016 11:01:43 +0200 | From | Peter Zijlstra <> | Subject | Re: lockdep WARNING in get_online_cpus |
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On Mon, Apr 04, 2016 at 10:19:05AM +0200, Dmitry Vyukov wrote: > > This happens in CONFIG_DEBUG_LOCKDEP code. Is it a bug in lockdep?
We hope not; but it is a new test.
So lockdep needs to check each current lock stack against the recorded lock dependencies to see if we've gotten ourselves a cycle. Doing this check is _expensive_.
So what lockdep does is it computes a hash for each lock stack and only if we've not seen this hash before (actually truncated since we don't have a full 64bit hashtable) do we go look for cycles.
The new check tries to detect hash-collisions in this cache. A collision would result in not checking for cycles, even if we've not seen the stack before.
You've managed to tickle this.
Now, last week I found some bugs in there, and Alfredo added a pretty printer, so maybe try and add these patches to your testing?
git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git locking/urgent
> But I always see at the same stack involving perf and jump_label...
So you have a simple reproducer? So that I can have a go at this.
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