On 04/02/2015 08:00 PM, tip-bot for Preeti U Murthy wrote: > Commit-ID: 345527b1edce8df719e0884500c76832a18211c3 > Gitweb: http://git.kernel.org/tip/345527b1edce8df719e0884500c76832a18211c3 > Author: Preeti U Murthy <pre...@linux.vnet.ibm.com> > AuthorDate: Mon, 30 Mar 2015 14:59:19 +0530 > Committer: Ingo Molnar <mi...@kernel.org> > CommitDate: Thu, 2 Apr 2015 14:25:39 +0200 > > clockevents: Fix cpu_down() race for hrtimer based broadcasting > > It was found when doing a hotplug stress test on POWER, that the > machine either hit softlockups or rcu_sched stall warnings. The > issue was traced to commit: > > 7cba160ad789 ("powernv/cpuidle: Redesign idle states management") > > which exposed the cpu_down() race with hrtimer based broadcast mode: > > 5d1638acb9f6 ("tick: Introduce hrtimer based broadcast") > > The race is the following: > > Assume CPU1 is the CPU which holds the hrtimer broadcasting duty > before it is taken down. > > CPU0 CPU1 > > cpu_down() take_cpu_down() > disable_interrupts() > > cpu_die() > > while (CPU1 != CPU_DEAD) { > msleep(100); > switch_to_idle(); > stop_cpu_timer(); > schedule_broadcast(); > } > > tick_cleanup_cpu_dead() > take_over_broadcast() > > So after CPU1 disabled interrupts it cannot handle the broadcast > hrtimer anymore, so CPU0 will be stuck forever. > > Fix this by explicitly taking over broadcast duty before cpu_die(). > > This is a temporary workaround. What we really want is a callback > in the clockevent device which allows us to do that from the dying > CPU by pushing the hrtimer onto a different cpu. That might involve > an IPI and is definitely more complex than this immediate fix. > > Changelog was picked up from: > > https://lkml.org/lkml/2015/2/16/213 > > Suggested-by: Thomas Gleixner <t...@linutronix.de> > Tested-by: Nicolas Pitre <n...@linaro.org> > Signed-off-by: Preeti U. Murthy <pre...@linux.vnet.ibm.com> > Cc: linuxppc-...@lists.ozlabs.org > Cc: m...@ellerman.id.au > Cc: nicolas.pi...@linaro.org > Cc: pet...@infradead.org > Cc: r...@rjwysocki.net > Fixes: > http://linuxppc.10917.n7.nabble.com/offlining-cpus-breakage-td88619.html > Link: > http://lkml.kernel.org/r/20150330092410.24979.59887.st...@preeti.in.ibm.com > [ Merged it to the latest timer tree, renamed the callback, tidied up the > changelog. ] > Signed-off-by: Ingo Molnar <mi...@kernel.org>
Can this be marked for stable too please? Regards Preeti U Murthy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
