On Tue, Dec 12, 2017 at 09:20:59AM -0800, Paul E. McKenney wrote: > The ARM implementation of arch_cpu_idle_dead() invokes complete(), but > does so after RCU has stopped watching the outgoing CPU, which results > in lockdep complaints because complete() invokes functions containing RCU > readers. This patch therefore uses Thomas Gleixner's trick of delegating > the complete() call to a surviving CPU via smp_call_function_single(). > > Reported-by: Peng Fan <[email protected]> > Reported-by: Russell King - ARM Linux <[email protected]> > Signed-off-by: Paul E. McKenney <[email protected]> > Tested-by: Tested-by: Fabio Estevam <[email protected]> > Cc: Russell King <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: "Peter Zijlstra (Intel)" <[email protected]> > Cc: Michal Hocko <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: <[email protected]>
As I just described in response to Fabio's testing, this doesn't solve anything if CONFIG_BL_SWITCHER is enabled. We could lose the unlock of a spinlock in the GIC code for sending the IPI. As I already said previously in our discussion (but I guess you just don't believe me): "2. there's some optional locking in the GIC driver that cause problems for the cpu dying path. The concensus last time around was that the IPI solution is a non- starter, so the seven year proven-reliable solution (disregarding the RCU warning) persists because I don't think anyone came up with a better solution." Using smp_call_function_single() invokes the IPI paths. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up According to speedtest.net: 8.21Mbps down 510kbps up
