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Date: Tue, 23 Jun 2015 12:09:32 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Oleg Nesterov <oleg@...hat.com> Cc: paulmck@...ux.vnet.ibm.com, tj@...nel.org, mingo@...hat.com, linux-kernel@...r.kernel.org, der.herr@...r.at, dave@...olabs.net, riel@...hat.com, viro@...IV.linux.org.uk, torvalds@...ux-foundation.org Subject: Re: [RFC][PATCH 12/13] stop_machine: Remove lglock On Tue, Jun 23, 2015 at 12:21:52AM +0200, Oleg Nesterov wrote: > Suppose that stop_two_cpus(cpu1 => 0, cpu2 => 1) races with stop_machine(). > > - stop_machine takes the lock on CPU 0, adds the work > and drops the lock > > - cpu_stop_queue_work() queues both works cpu_stop_queue_work() only ever queues _1_ work. > - stop_machine takes the lock on CPU 1, etc > > In this case both CPU 0 and 1 will run multi_cpu_stop() but they will > use different multi_stop_data's, so they will wait for each other > forever? So what you're saying is: queue_stop_cpus_work() stop_two_cpus() cpu_stop_queue_work(0,..); spin_lock(0); spin_lock(1); __cpu_stop_queue_work(0,..); __cpu_stop_queue_work(1,..); spin_unlock(1); spin_unlock(0); cpu_stop_queue_work(1,..); Indeed, I don't know what I was thinking... We can of course slap a percpu-rwsem in, but I wonder if there's anything smarter we can do here. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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