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Message-ID: <20150316183743.GA21453@linux.vnet.ibm.com> Date: Mon, 16 Mar 2015 11:37:43 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: linux-kernel@...r.kernel.org Cc: mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com Subject: [PATCH v2 tip/core/rcu 0/22] CPU hotplug updates for v4.1 Hello! This series updates RCU's handling of CPU hotplug offline operations, allowing RCU to have a precise notification of when it should start ignoring a CPU. This allowed detection of some illegal use of RCU by offline CPUs, and this series contains fixes for these. A similar problem exists for CPU onlining, but will be addressed later. One CPU-hotplug dragon at a time. 1. Add common code for notification from dying CPU. This is part of the fix for issues uncovered by improved detection, but is placed first to avoid messing up bisection. 2-4. Use #1 for x86, blackfin, and metag. (ARM also has this problem, but ARM's maintainers are working on their own fix.) 5. Remove duplicate offline-CPU callback-list initialization. This simplifies later changes to RCU's handling of offlining operations. 6. Improve code readability in rcu_cleanup_dead_cpu(). Simple code motion, no semantic change. 7. Eliminate a boolean variable and "if" statement by rearranging sync_rcu_preempt_exp_init()'s checks for CPUs not having blocked tasks. 8. Eliminate empty CONFIG_HOTPLUG_CPU #ifdef. 9. Add diagnostics to detect when RCU CPU stall warnings have been caused by failure to propagate quiescent states up the rcu_node combining tree. 10. Provide CONFIG_RCU_TORTURE_TEST_SLOW_INIT Kconfig option to artificially slow down grace-period initialization, thus increasing the probability of detecting races with this initialization process. 11. Update data files to enable CONFIG_RCU_TORTURE_TEST_SLOW_INIT by default during rcutorture testing, but leave the default time at zero. This default may be overridden by passing "--bootargs rcutree.gp_init_delay=1" to kvm.sh. 12. Remove event tracing from rcu_cpu_notify(), which is invoked by offline CPUs. (Event tracing uses RCU.) 13. Change meaning of ->expmask bitmasks to track blocked tasks rather than online CPUs. 14. Move rcu_report_unblock_qs_rnp() to common code. This will make it easier to provide proper locking protection. 15. Avoid races between CPU-hotplug operations and RCU grace-period initialization by processing CPU-hotplug changes only at the start of each grace period. This works because RCU need not wait on a CPU that came online after the start of the current grace period. 16. Eliminate the no-longer-needed ->onoff_mutex from the rcu_node structure. This is the only sleeplock acquired during RCU's CPU-hotplug processing, which in turn allows rcu_cpu_notify() to be invoked from the preemption-disabled idle loop. 17. Use a per-CPU variable to make the CPU-offline idle-loop transition point precise. (RCU's magic one-jiffy grace-period wait for offline CPUs must remain until the analogous online issue is addressed.) 18. Invoke rcu_cpu_notify() with a new CPU_DYING_IDLE op just before the idle-loop invocation of arch_cpu_idle_dead(). 19. Now that CPU-hotplug events are applied only during grace-period initialization, it is safe to unconditionally enable slow grace-period initialization for rcutorture testing. Note that this delay is applied randomly in order to get a good mix of fast and slow grace-period initialization. 20. Add checks that all quiescent states were received at grace-period cleanup time. 21. Add a check for the last task on a given RCU-node structure leaving its RCU read-side critical section between the time that hotplug information is propagated up the tree and the time that the grace period starts. 22. Add checks for grace-period number to all propagations of quiescent states up the rcu_node combining tree. These are required because a new grace period could start during this propagation due to the resolution of #21 above. (Thanks to Sasha Levin for exposing this bug during the course of his testing.) Changes since v1: o Fixed per-CPU state mechine to work correctly for architectures that online CPUs without needing to check whether or not previous offline operations completed correctly and on time, thanks to James Hogan. o Fixed Xen's interfacing to the common-code notifications, thanks to Boris Ostrovsky. o Added two fixes for handling of quiescent states and grace periods given the updated handling of CPU hotplug. Thanx, Paul ------------------------------------------------------------------------ b/Documentation/kernel-parameters.txt | 6 b/arch/blackfin/mach-common/smp.c | 6 b/arch/metag/kernel/smp.c | 5 b/arch/x86/include/asm/cpu.h | 2 b/arch/x86/include/asm/smp.h | 2 b/arch/x86/kernel/smpboot.c | 39 - b/arch/x86/xen/smp.c | 46 - b/include/linux/cpu.h | 14 b/include/linux/rcupdate.h | 2 b/kernel/cpu.c | 4 b/kernel/rcu/tree.c | 356 ++++++++++---- b/kernel/rcu/tree.h | 11 b/kernel/rcu/tree_plugin.h | 169 +++--- b/kernel/rcu/tree_trace.c | 4 b/kernel/sched/idle.c | 9 b/kernel/smpboot.c | 156 ++++++ b/lib/Kconfig.debug | 26 - b/tools/testing/selftests/rcutorture/configs/rcu/CFcommon | 1 18 files changed, 617 insertions(+), 241 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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