* Martin Schwidefsky <schwidefsky@xxxxxxxxxx> wrote: > On Fri, 28 Aug 2009 18:34:00 GMT > tip-bot for Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > > Commit-ID: 7285dd7fd375763bfb8ab1ac9cf3f1206f503c16 > > Gitweb: http://git.kernel.org/tip/7285dd7fd375763bfb8ab1ac9cf3f1206f503c16 > > Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > AuthorDate: Fri, 28 Aug 2009 20:25:24 +0200 > > Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > CommitDate: Fri, 28 Aug 2009 20:25:24 +0200 > > > > clocksource: Resolve cpu hotplug dead lock with TSC unstable > > > > Martin Schwidefsky analyzed it: > > To register a clocksource the clocksource_mutex is acquired and if > > necessary timekeeping_notify is called to install the clocksource as > > the timekeeper clock. timekeeping_notify uses stop_machine which needs > > to take cpu_add_remove_lock mutex. > > Starting a new cpu is done with the cpu_add_remove_lock mutex held. > > native_cpu_up checks the tsc of the new cpu and if the tsc is no good > > clocksource_change_rating is called. Which needs the clocksource_mutex > > and the deadlock is complete. > > > > The solution is to replace the TSC via the clocksource watchdog > > mechanism. Mark the TSC as unstable and schedule the watchdog work so > > it gets removed in the watchdog thread context. > > > > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > LKML-Reference: <new-submission> > > Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx> > > Cc: John Stultz <johnstul@xxxxxxxxxx> > > Ah, very good. I've been going round in circles to find a solution > that allows to downgrade the tsc rating when the second cpu is > enabled. Could not find a solution. Your approach changes > semantics slightly: the tsc clock will continue with its old > rating for a while until the watchdog will do the downgrade. If > that is acceptable then this is a good solution. Latest timers/core also passed thousands of iterations of -tip testing so far, so that painful series of locking and stability troubles has been solved and the bits look good for v2.6.32. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html