On 01/27/2015 09:01 AM, Preeti U Murthy wrote: > On 01/22/2015 04:45 PM, Thomas Gleixner wrote: >> On Thu, 22 Jan 2015, Preeti U Murthy wrote: >>> On 01/21/2015 05:16 PM, Thomas Gleixner wrote: >>> How about when the cpu that is going offline receives a timer interrupt >>> just before setting its state to CPU_DEAD ? That is still possible right >>> given that its clock devices may not have been shutdown and it is >>> capable of receiving interrupts for a short duration. Even with the >>> above patch, is the following scenario possible ? >>> >>> CPU0 CPU1 >>> t0 Receives timer interrupt >>> >>> t1 Sees that there are hrtimers >>> to be serviced (hrtimers are not yet migrated) >>> >>> t2 calls hrtimer_interrupt() >>> >>> t3 tick_program_event() CPU_DEAD notifiers >>> CPU0's td->evtdev = NULL >>> >>> t4 clockevent_program_event() >>> references NULL tick device pointer >>> >>> So my concern is that since the CLOCK_EVT_NOTIFY_CPU_DEAD callback >>> handles shutting down of devices besides moving tick related duties. >>> it's functions may race with the hotplug cpu still handling tick events. >> >> __cpu_disable() is supposed to block interrupts on the dying cpu. >> >> But I agree, we should make it more robust. So we want an explicit >> call for disabling the cpu local stuff and an explicit takeover of the >> broadcast duty. I'm anyway distangling the clockevents_notify() stuff, >> so it should be simple to do so.
Thomas ping. Would you be posting this patch? > > I noticed that tick_handover_do_timer() function also suffers from the > issue that the patch I posted for moving the broadcast duty had, in that > it relies on all cpus participating in stop_machine(). In a design where > all cpus do not participate in stop_machine(), if the freshly nominated > do_timer cpu is idle, there is no update of jiffies till that cpu gets > back to being busy. So we must do an explicit take over of *both* the > broadcast and do_timer duty just before the CPU_DEAD phase. Regards Preeti u Murthy _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
