On 04/03/2015 04:20 PM, Ingo Molnar wrote: > > * Preeti U Murthy <[email protected]> wrote: > >> 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 <[email protected]> >>> AuthorDate: Mon, 30 Mar 2015 14:59:19 +0530 >>> Committer: Ingo Molnar <[email protected]> >>> 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 <[email protected]> >>> Tested-by: Nicolas Pitre <[email protected]> >>> Signed-off-by: Preeti U. Murthy <[email protected]> >>> Cc: [email protected] >>> Cc: [email protected] >>> Cc: [email protected] >>> Cc: [email protected] >>> Cc: [email protected] >>> Fixes: >>> http://linuxppc.10917.n7.nabble.com/offlining-cpus-breakage-td88619.html >>> Link: >>> http://lkml.kernel.org/r/[email protected] >>> [ Merged it to the latest timer tree, renamed the callback, tidied up the >>> changelog. ] >>> Signed-off-by: Ingo Molnar <[email protected]> >> >> Can this be marked for stable too please? > > It can be forwarded to -stable once it has gone upstream in the merge > window and has gone through some testing upstream as well. The > breakage itself was introduced in the v3.19 merge window, so it's an > older regression - and the fix is not simple either.
Ok I see. Thanks Regards Preeti U Murthy > > Thanks, > > Ingo > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
