Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753934AbaBEWKG (ORCPT ); Wed, 5 Feb 2014 17:10:06 -0500 Received: from e23smtp03.au.ibm.com ([202.81.31.145]:48757 "EHLO e23smtp03.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751667AbaBEWKC (ORCPT ); Wed, 5 Feb 2014 17:10:02 -0500 From: "Srivatsa S. Bhat" Subject: [PATCH 00/51] CPU hotplug: Fix issues with callback registration To: paulus@samba.org, oleg@redhat.com, rusty@rustcorp.com.au, peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org Cc: mingo@kernel.org, paulmck@linux.vnet.ibm.com, tj@kernel.org, walken@google.com, ego@linux.vnet.ibm.com, linux@arm.linux.org.uk, linux-kernel@vger.kernel.org, srivatsa.bhat@linux.vnet.ibm.com Date: Thu, 06 Feb 2014 03:34:36 +0530 Message-ID: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14020522-6102-0000-0000-000004E447AD Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Many subsystems and drivers have the need to register CPU hotplug callbacks from their init routines and also perform initialization for the CPUs that are already online. But unfortunately there is no race-free way to achieve this today. For example, consider this piece of code: get_online_cpus(); for_each_online_cpu(cpu) init_cpu(cpu); register_cpu_notifier(&foobar_cpu_notifier); put_online_cpus(); This is not safe because there is a possibility of an ABBA deadlock involving the cpu_add_remove_lock and the cpu_hotplug.lock. CPU 0 CPU 1 ----- ----- Acquire cpu_hotplug.lock [via get_online_cpus()] CPU online/offline operation takes cpu_add_remove_lock [via cpu_maps_update_begin()] Try to acquire cpu_add_remove_lock [via register_cpu_notifier()] CPU online/offline operation tries to acquire cpu_hotplug.lock [via cpu_hotplug_begin()] *** DEADLOCK! *** Other combinations of callback registration also don't work correctly. Examples: register_cpu_notifier(&foobar_cpu_notifier); get_online_cpus(); for_each_online_cpu(cpu) init_cpu(cpu); put_online_cpus(); This can lead to double initialization if a hotplug operation occurs after registering the notifier and before invoking get_online_cpus(). On the other hand, the following piece of code can miss hotplug events altogether: get_online_cpus(); for_each_online_cpu(cpu) init_cpu(cpu); put_online_cpus(); ^ | Race window; Can miss hotplug events here v register_cpu_notifier(&foobar_cpu_notifier); To solve these issues and provide a race-free method to register CPU hotplug callbacks, this patchset introduces new variants of the callback registration APIs that don't hold the cpu_add_remove_lock, and exports the cpu_add_remove_lock via cpu_maps_update_begin/done() for use by various subsystems. With this in place, the following code snippet will register a hotplug callback as well as initialize already online CPUs without any race conditions. cpu_maps_update_begin(); for_each_online_cpu(cpu) init_cpu(cpu); /* This doesn't take the cpu_add_remove_lock */ __register_cpu_notifier(&foobar_cpu_notifier); cpu_maps_update_done(); This patchset introduces this infrastructure in patch 1, and performs tree-wide conversions (to use this model) in the remaining patches. This patchset has been hosted in the below git tree. It applies cleanly on v3.14-rc1. git://github.com/srivatsabhat/linux.git cpuhp-registration-fixes-v1 Oleg, I have incorporated your fix for raid5 in this patchset, and modified the patch a bit to handle the unregister_cpu_notifier() case as well. If you are fine with that patch (patch 45), can you kindly provide your Signed-off-by for that? Thank you! Oleg Nesterov (1): md, raid5: Fix CPU hotplug callback registration Srivatsa S. Bhat (50): CPU hotplug: Provide lockless versions of callback registration functions Doc/cpu-hotplug: Specify race-free way to register CPU hotplug callbacks CPU hotplug, perf: Fix CPU hotplug callback registration ia64, salinfo: Fix hotplug callback registration ia64, palinfo: Fix CPU hotplug callback registration ia64, topology: Fix CPU hotplug callback registration ia64, err-inject: Fix CPU hotplug callback registration arm, hw-breakpoint: Fix CPU hotplug callback registration arm, kvm: Fix CPU hotplug callback registration s390, cacheinfo: Fix CPU hotplug callback registration s390, smp: Fix CPU hotplug callback registration sparc, sysfs: Fix CPU hotplug callback registration powerpc, sysfs: Fix CPU hotplug callback registration x86, msr: Fix CPU hotplug callback registration x86, cpuid: Fix CPU hotplug callback registration x86, vsyscall: Fix CPU hotplug callback registration x86, intel, uncore: Fix CPU hotplug callback registration x86, mce: Fix CPU hotplug callback registration x86, therm_throt.c: Fix CPU hotplug callback registration x86, amd, ibs: Fix CPU hotplug callback registration x86, intel, cacheinfo: Fix CPU hotplug callback registration x86, intel, rapl: Fix CPU hotplug callback registration x86, amd, uncore: Fix CPU hotplug callback registration x86, hpet: Fix CPU hotplug callback registration x86, pci, amd-bus: Fix CPU hotplug callback registration x86, oprofile, nmi: Fix CPU hotplug callback registration x86, kvm: Fix CPU hotplug callback registration arm64, hw_breakpoint.c: Fix CPU hotplug callback registration arm64, debug-monitors: Fix CPU hotplug callback registration powercap, intel-rapl: Fix CPU hotplug callback registration scsi, bnx2i: Fix CPU hotplug callback registration scsi, bnx2fc: Fix CPU hotplug callback registration scsi, fcoe: Fix CPU hotplug callback registration zsmalloc: Fix CPU hotplug callback registration acpi-cpufreq: Fix CPU hotplug callback registration drivers/base/topology.c: Fix CPU hotplug callback registration clocksource, dummy-timer: Fix CPU hotplug callback registration intel-idle: Fix CPU hotplug callback registration oprofile, nmi-timer: Fix CPU hotplug callback registration octeon, watchdog: Fix CPU hotplug callback registration thermal, x86-pkg-temp: Fix CPU hotplug callback registration hwmon, coretemp: Fix CPU hotplug callback registration hwmon, via-cputemp: Fix CPU hotplug callback registration xen, balloon: Fix CPU hotplug callback registration trace, ring-buffer: Fix CPU hotplug callback registration profile: Fix CPU hotplug callback registration mm, vmstat: Fix CPU hotplug callback registration mm, zswap: Fix CPU hotplug callback registration net/core/flow.c: Fix CPU hotplug callback registration net/iucv/iucv.c: Fix CPU hotplug callback registration Documentation/cpu-hotplug.txt | 45 +++++++++ arch/arm/kernel/hw_breakpoint.c | 8 +- arch/arm/kvm/arm.c | 7 + arch/arm64/kernel/debug-monitors.c | 6 + arch/arm64/kernel/hw_breakpoint.c | 7 + arch/ia64/kernel/err_inject.c | 15 +++ arch/ia64/kernel/palinfo.c | 6 + arch/ia64/kernel/salinfo.c | 6 + arch/ia64/kernel/topology.c | 6 + arch/powerpc/kernel/sysfs.c | 8 +- arch/s390/kernel/cache.c | 5 + arch/s390/kernel/smp.c | 13 ++- arch/sparc/kernel/sysfs.c | 6 + arch/x86/kernel/cpu/intel_cacheinfo.c | 13 ++- arch/x86/kernel/cpu/mcheck/mce.c | 8 +- arch/x86/kernel/cpu/mcheck/therm_throt.c | 5 + arch/x86/kernel/cpu/perf_event_amd_ibs.c | 6 + arch/x86/kernel/cpu/perf_event_amd_uncore.c | 7 + arch/x86/kernel/cpu/perf_event_intel_rapl.c | 9 +- arch/x86/kernel/cpu/perf_event_intel_uncore.c | 6 + arch/x86/kernel/cpuid.c | 15 ++- arch/x86/kernel/hpet.c | 4 + arch/x86/kernel/msr.c | 16 ++- arch/x86/kernel/vsyscall_64.c | 6 + arch/x86/kvm/x86.c | 7 + arch/x86/oprofile/nmi_int.c | 15 +++ arch/x86/pci/amd_bus.c | 5 + drivers/base/topology.c | 12 ++ drivers/clocksource/dummy_timer.c | 11 ++ drivers/cpufreq/acpi-cpufreq.c | 7 + drivers/hwmon/coretemp.c | 14 +-- drivers/hwmon/via-cputemp.c | 14 +-- drivers/idle/intel_idle.c | 12 ++ drivers/md/raid5.c | 90 +++++++++---------- drivers/oprofile/nmi_timer_int.c | 23 +++-- drivers/powercap/intel_rapl.c | 10 ++ drivers/scsi/bnx2fc/bnx2fc_fcoe.c | 12 ++ drivers/scsi/bnx2i/bnx2i_init.c | 12 ++ drivers/scsi/fcoe/fcoe.c | 15 +++ drivers/thermal/x86_pkg_temp_thermal.c | 14 +-- drivers/watchdog/octeon-wdt-main.c | 11 ++ drivers/xen/balloon.c | 35 +++++-- include/linux/cpu.h | 36 +++++++ include/linux/perf_event.h | 16 +++ kernel/cpu.c | 20 ++++ kernel/profile.c | 20 +++- kernel/trace/ring_buffer.c | 19 ++-- mm/vmstat.c | 6 + mm/zsmalloc.c | 17 +++- mm/zswap.c | 8 +- net/core/flow.c | 8 +- net/iucv/iucv.c | 121 ++++++++++++------------- 52 files changed, 564 insertions(+), 259 deletions(-) Regards, Srivatsa S. 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