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Violators will be prosecuted for from ; Sun, 23 Jun 2013 23:32:46 +1000 Received: from d23relay04.au.ibm.com (d23relay04.au.ibm.com [9.190.234.120]) by d23dlp03.au.ibm.com (Postfix) with ESMTP id A9CA83578045 for ; Sun, 23 Jun 2013 23:42:07 +1000 (EST) Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139]) by d23relay04.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r5NDRK9V5308884 for ; Sun, 23 Jun 2013 23:27:20 +1000 Received: from d23av04.au.ibm.com (loopback [127.0.0.1]) by d23av04.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r5NDg5eo023065 for ; Sun, 23 Jun 2013 23:42:07 +1000 From: "Srivatsa S. Bhat" Subject: [PATCH 04/45] CPU hotplug: Add infrastructure to check lacking hotplug synchronization To: tglx@linutronix.de, peterz@infradead.org, tj@kernel.org, oleg@redhat.com, paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org, walken@google.com, vincent.guittot@linaro.org, laijs@cn.fujitsu.com Date: Sun, 23 Jun 2013 19:08:45 +0530 Message-ID: <20130623133841.19094.69631.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20130623133642.19094.16038.stgit@srivatsabhat.in.ibm.com> References: <20130623133642.19094.16038.stgit@srivatsabhat.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Cc: linux-arch@vger.kernel.org, Alex Shi , nikunj@linux.vnet.ibm.com, zhong@linux.vnet.ibm.com, linux-pm@vger.kernel.org, fweisbec@gmail.com, Rusty Russell , linux-kernel@vger.kernel.org, rostedt@goodmis.org, xiaoguangrong@linux.vnet.ibm.com, "Rafael J. Wysocki" , sbw@mit.edu, Yasuaki Ishimatsu , wangyun@linux.vnet.ibm.com, srivatsa.bhat@linux.vnet.ibm.com, netdev@vger.kernel.org, Tejun Heo , Thomas Gleixner , KOSAKI Motohiro , linuxppc-dev@lists.ozlabs.org, Andrew Morton List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Add a debugging infrastructure to warn if an atomic hotplug reader has not invoked get_online_cpus_atomic() before traversing/accessing the cpu_online_mask. Encapsulate these checks under a new debug config option DEBUG_HOTPLUG_CPU. This debugging infrastructure proves useful in the tree-wide conversion of atomic hotplug readers from preempt_disable() to the new APIs, and help us catch the places we missed, much before we actually get rid of stop_machine(). We can perhaps remove the debugging checks later on. Cc: Rusty Russell Cc: Alex Shi Cc: KOSAKI Motohiro Cc: Tejun Heo Cc: Thomas Gleixner Cc: Andrew Morton Cc: Yasuaki Ishimatsu Cc: "Rafael J. Wysocki" Signed-off-by: Srivatsa S. Bhat --- include/linux/cpumask.h | 12 ++++++++ kernel/cpu.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 87 insertions(+) diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h index d08e4d2..9197ca4 100644 --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -101,6 +101,18 @@ extern const struct cpumask *const cpu_active_mask; #define cpu_active(cpu) ((cpu) == 0) #endif +#ifdef CONFIG_DEBUG_HOTPLUG_CPU +extern void check_hotplug_safe_cpumask(const struct cpumask *mask); +extern void check_hotplug_safe_cpu(unsigned int cpu, + const struct cpumask *mask); +#else +static inline void check_hotplug_safe_cpumask(const struct cpumask *mask) { } +static inline void check_hotplug_safe_cpu(unsigned int cpu, + const struct cpumask *mask) +{ +} +#endif + /* verify cpu argument to cpumask_* operators */ static inline unsigned int cpumask_check(unsigned int cpu) { diff --git a/kernel/cpu.c b/kernel/cpu.c index 860f51a..e90d9d7 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -63,6 +63,72 @@ static struct { .refcount = 0, }; +#ifdef CONFIG_DEBUG_HOTPLUG_CPU + +static DEFINE_PER_CPU(unsigned long, atomic_reader_refcnt); + +static int current_is_hotplug_safe(const struct cpumask *mask) +{ + + /* If we are not dealing with cpu_online_mask, don't complain. */ + if (mask != cpu_online_mask) + return 1; + + /* If this is the task doing hotplug, don't complain. */ + if (unlikely(current == cpu_hotplug.active_writer)) + return 1; + + /* If we are in early boot, don't complain. */ + if (system_state != SYSTEM_RUNNING) + return 1; + + /* + * Check if the current task is in atomic context and it has + * invoked get_online_cpus_atomic() to synchronize with + * CPU Hotplug. + */ + if (preempt_count() || irqs_disabled()) + return this_cpu_read(atomic_reader_refcnt); + else + return 1; /* No checks for non-atomic contexts for now */ +} + +static inline void warn_hotplug_unsafe(void) +{ + WARN_ONCE(1, "Must use get/put_online_cpus_atomic() to synchronize" + " with CPU hotplug\n"); +} + +/* + * Check if the task (executing in atomic context) has the required protection + * against CPU hotplug, while accessing the specified cpumask. + */ +void check_hotplug_safe_cpumask(const struct cpumask *mask) +{ + if (!current_is_hotplug_safe(mask)) + warn_hotplug_unsafe(); +} +EXPORT_SYMBOL_GPL(check_hotplug_safe_cpumask); + +/* + * Similar to check_hotplug_safe_cpumask(), except that we don't complain + * if the task (executing in atomic context) is testing whether the CPU it + * is executing on is online or not. + * + * (A task executing with preemption disabled on a CPU, automatically prevents + * offlining that CPU, irrespective of the actual implementation of CPU + * offline. So we don't enforce holding of get_online_cpus_atomic() for that + * case). + */ +void check_hotplug_safe_cpu(unsigned int cpu, const struct cpumask *mask) +{ + if(!current_is_hotplug_safe(mask) && cpu != smp_processor_id()) + warn_hotplug_unsafe(); +} +EXPORT_SYMBOL_GPL(check_hotplug_safe_cpu); + +#endif + void get_online_cpus(void) { might_sleep(); @@ -189,13 +255,22 @@ unsigned int get_online_cpus_atomic(void) * from going offline. */ preempt_disable(); + +#ifdef CONFIG_DEBUG_HOTPLUG_CPU + this_cpu_inc(atomic_reader_refcnt); +#endif return smp_processor_id(); } EXPORT_SYMBOL_GPL(get_online_cpus_atomic); void put_online_cpus_atomic(void) { + +#ifdef CONFIG_DEBUG_HOTPLUG_CPU + this_cpu_dec(atomic_reader_refcnt); +#endif preempt_enable(); + } EXPORT_SYMBOL_GPL(put_online_cpus_atomic);