Messages in this thread | | | Date | Thu, 01 Apr 2010 14:05:44 +0800 | From | Cong Wang <> | Subject | Re: [Patch] workqueue: move lockdep annotations up to destroy_workqueue() |
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Cong Wang wrote: > Tejun Heo wrote: >> Hello, >> >> On 04/01/2010 01:28 PM, Cong Wang wrote: >>>> Hmmm... can you please try to see whether this circular locking >>>> warning involving wq->lockdep_map is reproducible w/ the bonding >>>> locking fixed? I still can't see where wq -> cpu_add_remove_lock >>>> dependency is created. >>>> >>> I thought this is obvious. >>> >>> Here it is: >>> >>> void destroy_workqueue(struct workqueue_struct *wq) >>> { >>> const struct cpumask *cpu_map = wq_cpu_map(wq); >>> int cpu; >>> >>> cpu_maps_update_begin(); <----------------- Hold >>> cpu_add_remove_lock here >>> spin_lock(&workqueue_lock); >>> list_del(&wq->list); >>> spin_unlock(&workqueue_lock); >>> >>> for_each_cpu(cpu, cpu_map) >>> cleanup_workqueue_thread(per_cpu_ptr(wq->cpu_wq, >>> cpu)); <------ See below >>> cpu_maps_update_done(); <----------------- Release >>> cpu_add_remove_lock here >>> >>> ... >>> static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq) >>> { >>> /* >>> * Our caller is either destroy_workqueue() or CPU_POST_DEAD, >>> * cpu_add_remove_lock protects cwq->thread. >>> */ >>> if (cwq->thread == NULL) >>> return; >>> >>> lock_map_acquire(&cwq->wq->lockdep_map); <-------------- Lockdep >>> complains here. >>> lock_map_release(&cwq->wq->lockdep_map); >>> ... >> >> Yeap, the above is cpu_add_remove_lock -> wq->lockdep_map dependency. >> I can see that but I'm failing to see where the dependency the other >> direction is created. >> > > Hmm, it looks like I misunderstand lock_map_acquire()? From the changelog, > I thought it was added to complain its caller is holding a lock when > invoking > it, thus cpu_add_remove_lock is not an exception. >
Oh, I see, wq->lockdep_map is acquired again in run_workqueue(), so I was wrong. :) I think you and Oleg are right, the lockdep warning is not irrelevant.
Sorry for the noise, ignore this patch please.
Thanks.
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