x86, bts, hw-branch-tracer: add _noirq variants to the debug store interface

The hw-branch-tracer uses debug store functions from an on_each_cpu()
context, which is simply wrong since the functions may sleep.

Add _noirq variants for most functions, which  may be called with
interrupts disabled.

Separate per-cpu and per-task tracing and allow per-cpu tracing to be
controlled from any cpu.

Make the hw-branch-tracer use the new debug store interface, synchronize
with hotplug cpu event using get/put_online_cpus(), and remove the
unnecessary spinlock.

Make the ptrace bts and the ds selftest code use the new interface.

Defer the ds selftest.

Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Cc: roland@redhat.com
Cc: eranian@googlemail.com
Cc: oleg@redhat.com
Cc: juan.villacis@intel.com
Cc: ak@linux.jf.intel.com
LKML-Reference: <20090403144555.658136000@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 72 insertions, 121 deletions

diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
index 8b2109a6c61c..50565d8cd2ed 100644
--- a/kernel/trace/trace_hw_branches.c
+++ b/kernel/trace/trace_hw_branches.c
@@ -4,7 +4,6 @@
  * Copyright (C) 2008-2009 Intel Corporation.
  * Markus Metzger <markus.t.metzger@gmail.com>, 2008-2009
  */
-#include <linux/spinlock.h>
 #include <linux/kallsyms.h>
 #include <linux/debugfs.h>
 #include <linux/ftrace.h>
@@ -21,168 +20,113 @@
 
 #define BTS_BUFFER_SIZE (1 << 13)
 
-/*
- * The tracer lock protects the below per-cpu tracer array.
- * It needs to be held to:
- * - start tracing on all cpus
- * - stop tracing on all cpus
- * - start tracing on a single hotplug cpu
- * - stop tracing on a single hotplug cpu
- * - read the trace from all cpus
- * - read the trace from a single cpu
- */
-static DEFINE_SPINLOCK(bts_tracer_lock);
 static DEFINE_PER_CPU(struct bts_tracer *, tracer);
 static DEFINE_PER_CPU(unsigned char[BTS_BUFFER_SIZE], buffer);
 
 #define this_tracer per_cpu(tracer, smp_processor_id())
-#define this_buffer per_cpu(buffer, smp_processor_id())
 
 static int trace_hw_branches_enabled __read_mostly;
 static int trace_hw_branches_suspended __read_mostly;
 static struct trace_array *hw_branch_trace __read_mostly;
 
 
-/*
- * Initialize the tracer for the current cpu.
- * The argument is ignored.
- *
- * pre: bts_tracer_lock must be locked.
- */
-static void bts_trace_init_cpu(void *arg)
+static void bts_trace_init_cpu(int cpu)
 {
-        if (this_tracer)
-                ds_release_bts(this_tracer);
+        per_cpu(tracer, cpu) =
+                ds_request_bts_cpu(cpu, per_cpu(buffer, cpu), BTS_BUFFER_SIZE,
+                                   NULL, (size_t)-1, BTS_KERNEL);
 
-        this_tracer = ds_request_bts(NULL, this_buffer, BTS_BUFFER_SIZE,
-                                     NULL, (size_t)-1, BTS_KERNEL);
-        if (IS_ERR(this_tracer)) {
-                this_tracer = NULL;
-                return;
-        }
+        if (IS_ERR(per_cpu(tracer, cpu)))
+                per_cpu(tracer, cpu) = NULL;
 }
 
 static int bts_trace_init(struct trace_array *tr)
 {
-        int cpu, avail;
-
-        spin_lock(&bts_tracer_lock);
+        int cpu;
 
         hw_branch_trace = tr;
+        trace_hw_branches_enabled = 0;
 
-        on_each_cpu(bts_trace_init_cpu, NULL, 1);
-
-        /* Check on how many cpus we could enable tracing */
-        avail = 0;
-        for_each_online_cpu(cpu)
-                if (per_cpu(tracer, cpu))
-                        avail++;
+        get_online_cpus();
+        for_each_online_cpu(cpu) {
+                bts_trace_init_cpu(cpu);
 
-        trace_hw_branches_enabled = (avail ? 1 : 0);
+                if (likely(per_cpu(tracer, cpu)))
+                        trace_hw_branches_enabled = 1;
+        }
         trace_hw_branches_suspended = 0;
-
-        spin_unlock(&bts_tracer_lock);
-
+        put_online_cpus();
 
         /* If we could not enable tracing on a single cpu, we fail. */
-        return avail ? 0 : -EOPNOTSUPP;
-}
-
-/*
- * Release the tracer for the current cpu.
- * The argument is ignored.
- *
- * pre: bts_tracer_lock must be locked.
- */
-static void bts_trace_release_cpu(void *arg)
-{
-        if (this_tracer) {
-                ds_release_bts(this_tracer);
-                this_tracer = NULL;
-        }
+        return trace_hw_branches_enabled ? 0 : -EOPNOTSUPP;
 }
 
 static void bts_trace_reset(struct trace_array *tr)
 {
-        spin_lock(&bts_tracer_lock);
+        int cpu;
 
-        on_each_cpu(bts_trace_release_cpu, NULL, 1);
+        get_online_cpus();
+        for_each_online_cpu(cpu) {
+                if (likely(per_cpu(tracer, cpu))) {
+                        ds_release_bts(per_cpu(tracer, cpu));
+                        per_cpu(tracer, cpu) = NULL;
+                }
+        }
         trace_hw_branches_enabled = 0;
         trace_hw_branches_suspended = 0;
-
-        spin_unlock(&bts_tracer_lock);
-}
-
-/*
- * Resume tracing on the current cpu.
- * The argument is ignored.
- *
- * pre: bts_tracer_lock must be locked.
- */
-static void bts_trace_resume_cpu(void *arg)
-{
-        if (this_tracer)
-                ds_resume_bts(this_tracer);
+        put_online_cpus();
 }
 
 static void bts_trace_start(struct trace_array *tr)
 {
-        spin_lock(&bts_tracer_lock);
+        int cpu;
 
-        on_each_cpu(bts_trace_resume_cpu, NULL, 1);
+        get_online_cpus();
+        for_each_online_cpu(cpu)
+                if (likely(per_cpu(tracer, cpu)))
+                        ds_resume_bts(per_cpu(tracer, cpu));
         trace_hw_branches_suspended = 0;
-
-        spin_unlock(&bts_tracer_lock);
-}
-
-/*
- * Suspend tracing on the current cpu.
- * The argument is ignored.
- *
- * pre: bts_tracer_lock must be locked.
- */
-static void bts_trace_suspend_cpu(void *arg)
-{
-        if (this_tracer)
-                ds_suspend_bts(this_tracer);
+        put_online_cpus();
 }
 
 static void bts_trace_stop(struct trace_array *tr)
 {
-        spin_lock(&bts_tracer_lock);
+        int cpu;
 
-        on_each_cpu(bts_trace_suspend_cpu, NULL, 1);
+        get_online_cpus();
+        for_each_online_cpu(cpu)
+                if (likely(per_cpu(tracer, cpu)))
+                        ds_suspend_bts(per_cpu(tracer, cpu));
         trace_hw_branches_suspended = 1;
-
-        spin_unlock(&bts_tracer_lock);
+        put_online_cpus();
 }
 
 static int __cpuinit bts_hotcpu_handler(struct notifier_block *nfb,
                                      unsigned long action, void *hcpu)
 {
-        unsigned int cpu = (unsigned long)hcpu;
-
-        spin_lock(&bts_tracer_lock);
-
-        if (!trace_hw_branches_enabled)
-                goto out;
+        int cpu = (long)hcpu;
 
         switch (action) {
         case CPU_ONLINE:
         case CPU_DOWN_FAILED:
-                smp_call_function_single(cpu, bts_trace_init_cpu, NULL, 1);
-
-                if (trace_hw_branches_suspended)
-                        smp_call_function_single(cpu, bts_trace_suspend_cpu,
-                                                 NULL, 1);
+                /* The notification is sent with interrupts enabled. */
+                if (trace_hw_branches_enabled) {
+                        bts_trace_init_cpu(cpu);
+
+                        if (trace_hw_branches_suspended &&
+                            likely(per_cpu(tracer, cpu)))
+                                ds_suspend_bts(per_cpu(tracer, cpu));
+                }
                 break;
+
         case CPU_DOWN_PREPARE:
-                smp_call_function_single(cpu, bts_trace_release_cpu, NULL, 1);
-                break;
+                /* The notification is sent with interrupts enabled. */
+                if (likely(per_cpu(tracer, cpu))) {
+                        ds_release_bts(per_cpu(tracer, cpu));
+                        per_cpu(tracer, cpu) = NULL;
+                }
         }
 
- out:
-        spin_unlock(&bts_tracer_lock);
         return NOTIFY_DONE;
 }
 
@@ -274,7 +218,7 @@ static void trace_bts_at(const struct bts_trace *trace, void *at)
 /*
  * Collect the trace on the current cpu and write it into the ftrace buffer.
  *
- * pre: bts_tracer_lock must be locked
+ * pre: tracing must be suspended on the current cpu
  */
 static void trace_bts_cpu(void *arg)
 {
@@ -291,10 +235,9 @@ static void trace_bts_cpu(void *arg)
         if (unlikely(!this_tracer))
                 return;
 
-        ds_suspend_bts(this_tracer);
         trace = ds_read_bts(this_tracer);
         if (!trace)
-                goto out;
+                return;
 
         for (at = trace->ds.top; (void *)at < trace->ds.end;
              at += trace->ds.size)
@@ -303,18 +246,27 @@ static void trace_bts_cpu(void *arg)
         for (at = trace->ds.begin; (void *)at < trace->ds.top;
              at += trace->ds.size)
                 trace_bts_at(trace, at);
-
-out:
-        ds_resume_bts(this_tracer);
 }
 
 static void trace_bts_prepare(struct trace_iterator *iter)
 {
-        spin_lock(&bts_tracer_lock);
+        int cpu;
 
+        get_online_cpus();
+        for_each_online_cpu(cpu)
+                if (likely(per_cpu(tracer, cpu)))
+                        ds_suspend_bts(per_cpu(tracer, cpu));
+        /*
+         * We need to collect the trace on the respective cpu since ftrace
+         * implicitly adds the record for the current cpu.
+         * Once that is more flexible, we could collect the data from any cpu.
+         */
         on_each_cpu(trace_bts_cpu, iter->tr, 1);
 
-        spin_unlock(&bts_tracer_lock);
+        for_each_online_cpu(cpu)
+                if (likely(per_cpu(tracer, cpu)))
+                        ds_resume_bts(per_cpu(tracer, cpu));
+        put_online_cpus();
 }
 
 static void trace_bts_close(struct trace_iterator *iter)
@@ -324,12 +276,11 @@ static void trace_bts_close(struct trace_iterator *iter)
 
 void trace_hw_branch_oops(void)
 {
-        spin_lock(&bts_tracer_lock);
-
-        if (trace_hw_branches_enabled)
+        if (this_tracer) {
+                ds_suspend_bts_noirq(this_tracer);
                 trace_bts_cpu(hw_branch_trace);
-
-        spin_unlock(&bts_tracer_lock);
+                ds_resume_bts_noirq(this_tracer);
+        }
 }
 
 struct tracer bts_tracer __read_mostly =