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.
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 > Thanks, > > tglx > > > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev@lists.ozlabs.org > https://lists.ozlabs.org/listinfo/linuxppc-dev > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
