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Date: Mon, 18 Sep 2017 12:29:31 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: Neeraj Upadhyay <neeraju@...eaurora.org>, josh@...htriplett.org, mathieu.desnoyers@...icios.com, jiangshanlai@...il.com, linux-kernel@...r.kernel.org, sramana@...eaurora.org, prsood@...eaurora.org, pkondeti@...eaurora.org, markivx@...eaurora.org, peterz@...radead.org Subject: Re: Query regarding synchronize_sched_expedited and resched_cpu On Mon, 18 Sep 2017 09:24:12 -0700 "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote: > As soon as I work through the backlog of lockdep complaints that > appeared in the last merge window... :-( > > sparse_irq_lock, I am looking at you!!! ;-) I just hit one too, and decided to write a patch to show a chain of 3 when applicable. For example: Chain exists of: cpu_hotplug_lock.rw_sem --> smpboot_threads_lock --> (complete)&self->parked Possible unsafe locking scenario by crosslock: CPU0 CPU1 CPU2 ---- ---- ---- lock(smpboot_threads_lock); lock((complete)&self->parked); lock(cpu_hotplug_lock.rw_sem); lock(smpboot_threads_lock); lock(cpu_hotplug_lock.rw_sem); unlock((complete)&self->parked); *** DEADLOCK *** :-) -- Steve
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