From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
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, David.Laight@aculab.com
Cc: linux-arch@vger.kernel.org, Alex Shi <alex.shi@intel.com>,
nikunj@linux.vnet.ibm.com, zhong@linux.vnet.ibm.com,
linux-pm@vger.kernel.org, fweisbec@gmail.com,
Rusty Russell <rusty@rustcorp.com.au>,
linux-kernel@vger.kernel.org, rostedt@goodmis.org,
xiaoguangrong@linux.vnet.ibm.com,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
sbw@mit.edu, Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
wangyun@linux.vnet.ibm.com,
"Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
netdev@vger.kernel.org, Tejun Heo <tj@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
linuxppc-dev@lists.ozlabs.org,
Andrew Morton <akpm@linux-foundation.org>
Subject: [PATCH v3 04/45] CPU hotplug: Add infrastructure to check lacking hotplug synchronization
Date: Fri, 28 Jun 2013 01:23:05 +0530 [thread overview]
Message-ID: <20130627195305.29830.10263.stgit@srivatsabhat.in.ibm.com> (raw)
In-Reply-To: <20130627195136.29830.10445.stgit@srivatsabhat.in.ibm.com>
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 <rusty@rustcorp.com.au>
Cc: Alex Shi <alex.shi@intel.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---
include/linux/cpumask.h | 12 ++++++
kernel/cpu.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 101 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..5297ec1 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -63,6 +63,92 @@ 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);
+
+static inline void atomic_reader_refcnt_inc(void)
+{
+ this_cpu_inc(atomic_reader_refcnt);
+}
+
+static inline void atomic_reader_refcnt_dec(void)
+{
+ this_cpu_dec(atomic_reader_refcnt);
+}
+
+#else
+
+static inline void atomic_reader_refcnt_inc(void)
+{
+}
+
+static inline void atomic_reader_refcnt_dec(void)
+{
+}
+
+#endif
+
void get_online_cpus(void)
{
might_sleep();
@@ -189,12 +275,15 @@ unsigned int get_online_cpus_atomic(void)
* from going offline.
*/
preempt_disable();
+ atomic_reader_refcnt_inc();
+
return smp_processor_id();
}
EXPORT_SYMBOL_GPL(get_online_cpus_atomic);
void put_online_cpus_atomic(void)
{
+ atomic_reader_refcnt_dec();
preempt_enable();
}
EXPORT_SYMBOL_GPL(put_online_cpus_atomic);
next prev parent reply other threads:[~2013-06-27 19:56 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-27 19:52 [PATCH v3 00/45] CPU hotplug: stop_machine()-free CPU hotplug, part 1 Srivatsa S. Bhat
2013-06-27 19:52 ` [PATCH v3 01/45] CPU hotplug: Provide APIs to prevent CPU offline from atomic context Srivatsa S. Bhat
2013-06-27 19:52 ` [PATCH v3 02/45] CPU hotplug: Clarify the usage of different synchronization APIs Srivatsa S. Bhat
2013-06-27 19:52 ` [PATCH v3 03/45] Documentation, CPU hotplug: Recommend usage of get/put_online_cpus_atomic() Srivatsa S. Bhat
2013-06-27 19:53 ` Srivatsa S. Bhat [this message]
2013-06-27 19:53 ` [PATCH v3 05/45] CPU hotplug: Protect set_cpu_online() to avoid false-positives Srivatsa S. Bhat
2013-06-27 19:53 ` [PATCH v3 06/45] CPU hotplug: Sprinkle debugging checks to catch locking bugs Srivatsa S. Bhat
2013-06-27 19:53 ` [PATCH v3 07/45] CPU hotplug: Add _nocheck() variants of accessor functions Srivatsa S. Bhat
2013-06-27 19:53 ` [PATCH v3 08/45] CPU hotplug: Expose the new debug config option Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 09/45] CPU hotplug: Convert preprocessor macros to static inline functions Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 10/45] smp: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-07-02 5:32 ` Michael Wang
2013-07-02 8:25 ` Srivatsa S. Bhat
2013-07-02 8:47 ` Michael Wang
2013-07-02 9:51 ` Srivatsa S. Bhat
2013-07-02 10:08 ` Michael Wang
2013-06-27 19:54 ` [PATCH v3 11/45] sched/core: " Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 12/45] migration: Use raw_spin_lock/unlock since interrupts are already disabled Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 13/45] sched/fair: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 14/45] timer: " Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 15/45] sched/rt: " Srivatsa S. Bhat
2013-06-27 19:55 ` [PATCH v3 16/45] rcu: Use cpu_is_offline_nocheck() to avoid false-positive warnings Srivatsa S. Bhat
2013-06-27 20:12 ` Paul E. McKenney
2013-06-27 19:55 ` [PATCH v3 17/45] tick-broadcast: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-27 19:55 ` [PATCH v3 18/45] time/clocksource: " Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 19/45] softirq: " Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 20/45] irq: " Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 21/45] net: " Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 22/45] block: " Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 23/45] percpu_counter: Use _nocheck version of for_each_online_cpu() Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 24/45] infiniband: ehca: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 25/45] [SCSI] fcoe: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 26/45] staging/octeon: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 27/45] x86: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 28/45] perf/x86: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 29/45] KVM: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 30/45] x86/xen: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 31/45] alpha/smp: " Srivatsa S. Bhat
2013-06-27 19:58 ` [PATCH v3 32/45] blackfin/smp: " Srivatsa S. Bhat
2013-06-27 19:58 ` [PATCH v3 33/45] cris/smp: " Srivatsa S. Bhat
2013-06-27 19:58 ` [PATCH v3 34/45] hexagon/smp: " Srivatsa S. Bhat
2013-06-27 19:58 ` [PATCH v3 35/45] ia64: irq, perfmon: " Srivatsa S. Bhat
2013-06-27 19:59 ` [PATCH v3 36/45] ia64: smp, tlb: " Srivatsa S. Bhat
2013-06-27 19:59 ` [PATCH v3 37/45] m32r: " Srivatsa S. Bhat
2013-06-27 19:59 ` [PATCH v3 38/45] MIPS: " Srivatsa S. Bhat
2013-06-27 19:59 ` [PATCH v3 39/45] mn10300: " Srivatsa S. Bhat
2013-06-27 19:59 ` [PATCH v3 40/45] powerpc, irq: Use GFP_ATOMIC allocations in atomic context Srivatsa S. Bhat
2013-06-27 20:00 ` [PATCH v3 41/45] powerpc: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-27 20:00 ` [PATCH v3 42/45] powerpc: Use get/put_online_cpus_atomic() to avoid false-positive warning Srivatsa S. Bhat
2013-06-27 20:00 ` [PATCH v3 43/45] sh: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-27 20:00 ` [PATCH v3 44/45] sparc: " Srivatsa S. Bhat
2013-06-27 20:00 ` [PATCH v3 45/45] tile: " Srivatsa S. Bhat
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