Messages in this thread | | | Date | Thu, 01 Apr 2010 14:07:24 +0800 | From | Cong Wang <> | Subject | Re: [Patch] workqueue: move lockdep annotations up to destroy_workqueue() |
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Cong Wang wrote: > 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. >
Oops, typo, I meant "is irrelevant." ;)
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