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, 367 insertions, 107 deletions

diff --git a/arch/x86/kernel/ds.c b/arch/x86/kernel/ds.c
index 2071b992c35c..21a3852abf68 100644
--- a/arch/x86/kernel/ds.c
+++ b/arch/x86/kernel/ds.c
@@ -245,60 +245,50 @@ struct ds_context {
         struct pebs_tracer      *pebs_master;
 
         /* Use count: */
-        unsigned long count;
+        unsigned long           count;
 
         /* Pointer to the context pointer field: */
         struct ds_context       **this;
 
-        /* The traced task; NULL for current cpu: */
+        /* The traced task; NULL for cpu tracing: */
         struct task_struct      *task;
-};
 
-static DEFINE_PER_CPU(struct ds_context *, system_context_array);
+        /* The traced cpu; only valid if task is NULL: */
+        int                     cpu;
+};
 
-#define system_context per_cpu(system_context_array, smp_processor_id())
+static DEFINE_PER_CPU(struct ds_context *, cpu_context);
 
 
-static inline struct ds_context *ds_get_context(struct task_struct *task)
+static struct ds_context *ds_get_context(struct task_struct *task, int cpu)
 {
         struct ds_context **p_context =
-                (task ? &task->thread.ds_ctx : &system_context);
+                (task ? &task->thread.ds_ctx : &per_cpu(cpu_context, cpu));
         struct ds_context *context = NULL;
         struct ds_context *new_context = NULL;
-        unsigned long irq;
 
-        /*
-         * Chances are small that we already have a context.
-         *
-         * Contexts for per-cpu tracing are allocated using
-         * smp_call_function(). We must not sleep.
-         */
-        new_context = kzalloc(sizeof(*new_context), GFP_ATOMIC);
+        /* Chances are small that we already have a context. */
+        new_context = kzalloc(sizeof(*new_context), GFP_KERNEL);
         if (!new_context)
                 return NULL;
 
-        spin_lock_irqsave(&ds_lock, irq);
+        spin_lock_irq(&ds_lock);
 
         context = *p_context;
-        if (!context) {
+        if (likely(!context)) {
                 context = new_context;
 
                 context->this = p_context;
                 context->task = task;
+                context->cpu = cpu;
                 context->count = 0;
 
-                if (task)
-                        set_tsk_thread_flag(task, TIF_DS_AREA_MSR);
-
-                if (!task || (task == current))
-                        wrmsrl(MSR_IA32_DS_AREA, (unsigned long)context->ds);
-
                 *p_context = context;
         }
 
         context->count++;
 
-        spin_unlock_irqrestore(&ds_lock, irq);
+        spin_unlock_irq(&ds_lock);
 
         if (context != new_context)
                 kfree(new_context);
@@ -306,7 +296,7 @@ static inline struct ds_context *ds_get_context(struct task_struct *task)
         return context;
 }
 
-static inline void ds_put_context(struct ds_context *context)
+static void ds_put_context(struct ds_context *context)
 {
         struct task_struct *task;
         unsigned long irq;
@@ -328,8 +318,15 @@ static inline void ds_put_context(struct ds_context *context)
         if (task)
                 clear_tsk_thread_flag(task, TIF_DS_AREA_MSR);
 
-        if (!task || (task == current))
-                wrmsrl(MSR_IA32_DS_AREA, 0);
+        /*
+         * We leave the (now dangling) pointer to the DS configuration in
+         * the DS_AREA msr. This is as good or as bad as replacing it with
+         * NULL - the hardware would crash if we enabled tracing.
+         *
+         * This saves us some problems with having to write an msr on a
+         * different cpu while preventing others from doing the same for the
+         * next context for that same cpu.
+         */
 
         spin_unlock_irqrestore(&ds_lock, irq);
 
@@ -340,6 +337,31 @@ static inline void ds_put_context(struct ds_context *context)
         kfree(context);
 }
 
+static void ds_install_ds_area(struct ds_context *context)
+{
+        unsigned long ds;
+
+        ds = (unsigned long)context->ds;
+
+        /*
+         * There is a race between the bts master and the pebs master.
+         *
+         * The thread/cpu access is synchronized via get/put_cpu() for
+         * task tracing and via wrmsr_on_cpu for cpu tracing.
+         *
+         * If bts and pebs are collected for the same task or same cpu,
+         * the same confiuration is written twice.
+         */
+        if (context->task) {
+                get_cpu();
+                if (context->task == current)
+                        wrmsrl(MSR_IA32_DS_AREA, ds);
+                set_tsk_thread_flag(context->task, TIF_DS_AREA_MSR);
+                put_cpu();
+        } else
+                wrmsr_on_cpu(context->cpu, MSR_IA32_DS_AREA,
+                             (u32)((u64)ds), (u32)((u64)ds >> 32));
+}
 
 /*
  * Call the tracer's callback on a buffer overflow.
@@ -622,6 +644,7 @@ static void ds_init_ds_trace(struct ds_trace *trace, enum ds_qualifier qual,
          * The value for 'no threshold' is -1, which will set the
          * threshold outside of the buffer, just like we want it.
          */
+        ith *= ds_cfg.sizeof_rec[qual];
         trace->ith = (void *)(buffer + size - ith);
 
         trace->flags = flags;
@@ -630,7 +653,7 @@ static void ds_init_ds_trace(struct ds_trace *trace, enum ds_qualifier qual,
 
 static int ds_request(struct ds_tracer *tracer, struct ds_trace *trace,
                       enum ds_qualifier qual, struct task_struct *task,
-                      void *base, size_t size, size_t th, unsigned int flags)
+                      int cpu, void *base, size_t size, size_t th)
 {
         struct ds_context *context;
         int error;
@@ -643,7 +666,7 @@ static int ds_request(struct ds_tracer *tracer, struct ds_trace *trace,
         if (!base)
                 goto out;
 
-        /* We require some space to do alignment adjustments below. */
+        /* We need space for alignment adjustments in ds_init_ds_trace(). */
         error = -EINVAL;
         if (size < (DS_ALIGNMENT + ds_cfg.sizeof_rec[qual]))
                 goto out;
@@ -660,25 +683,27 @@ static int ds_request(struct ds_tracer *tracer, struct ds_trace *trace,
         tracer->size = size;
 
         error = -ENOMEM;
-        context = ds_get_context(task);
+        context = ds_get_context(task, cpu);
         if (!context)
                 goto out;
         tracer->context = context;
 
-        ds_init_ds_trace(trace, qual, base, size, th, flags);
+        /*
+         * Defer any tracer-specific initialization work for the context until
+         * context ownership has been clarified.
+         */
 
         error = 0;
  out:
         return error;
 }
 
-struct bts_tracer *ds_request_bts(struct task_struct *task,
-                                  void *base, size_t size,
-                                  bts_ovfl_callback_t ovfl, size_t th,
-                                  unsigned int flags)
+static struct bts_tracer *ds_request_bts(struct task_struct *task, int cpu,
+                                         void *base, size_t size,
+                                         bts_ovfl_callback_t ovfl, size_t th,
+                                         unsigned int flags)
 {
         struct bts_tracer *tracer;
-        unsigned long irq;
         int error;
 
         /* Buffer overflow notification is not yet implemented. */
@@ -690,42 +715,46 @@ struct bts_tracer *ds_request_bts(struct task_struct *task,
         if (error < 0)
                 goto out;
 
-        /*
-         * Per-cpu tracing is typically requested using smp_call_function().
-         * We must not sleep.
-         */
         error = -ENOMEM;
-        tracer = kzalloc(sizeof(*tracer), GFP_ATOMIC);
+        tracer = kzalloc(sizeof(*tracer), GFP_KERNEL);
         if (!tracer)
                 goto out_put_tracer;
         tracer->ovfl = ovfl;
 
+        /* Do some more error checking and acquire a tracing context. */
         error = ds_request(&tracer->ds, &tracer->trace.ds,
-                           ds_bts, task, base, size, th, flags);
+                           ds_bts, task, cpu, base, size, th);
         if (error < 0)
                 goto out_tracer;
 
-
-        spin_lock_irqsave(&ds_lock, irq);
+        /* Claim the bts part of the tracing context we acquired above. */
+        spin_lock_irq(&ds_lock);
 
         error = -EPERM;
         if (tracer->ds.context->bts_master)
                 goto out_unlock;
         tracer->ds.context->bts_master = tracer;
 
-        spin_unlock_irqrestore(&ds_lock, irq);
+        spin_unlock_irq(&ds_lock);
 
+        /*
+         * Now that we own the bts part of the context, let's complete the
+         * initialization for that part.
+         */
+        ds_init_ds_trace(&tracer->trace.ds, ds_bts, base, size, th, flags);
+        ds_write_config(tracer->ds.context, &tracer->trace.ds, ds_bts);
+        ds_install_ds_area(tracer->ds.context);
 
         tracer->trace.read  = bts_read;
         tracer->trace.write = bts_write;
 
-        ds_write_config(tracer->ds.context, &tracer->trace.ds, ds_bts);
+        /* Start tracing. */
         ds_resume_bts(tracer);
 
         return tracer;
 
  out_unlock:
-        spin_unlock_irqrestore(&ds_lock, irq);
+        spin_unlock_irq(&ds_lock);
         ds_put_context(tracer->ds.context);
  out_tracer:
         kfree(tracer);
@@ -735,13 +764,27 @@ struct bts_tracer *ds_request_bts(struct task_struct *task,
         return ERR_PTR(error);
 }
 
-struct pebs_tracer *ds_request_pebs(struct task_struct *task,
-                                    void *base, size_t size,
-                                    pebs_ovfl_callback_t ovfl, size_t th,
-                                    unsigned int flags)
+struct bts_tracer *ds_request_bts_task(struct task_struct *task,
+                                       void *base, size_t size,
+                                       bts_ovfl_callback_t ovfl,
+                                       size_t th, unsigned int flags)
+{
+        return ds_request_bts(task, 0, base, size, ovfl, th, flags);
+}
+
+struct bts_tracer *ds_request_bts_cpu(int cpu, void *base, size_t size,
+                                      bts_ovfl_callback_t ovfl,
+                                      size_t th, unsigned int flags)
+{
+        return ds_request_bts(NULL, cpu, base, size, ovfl, th, flags);
+}
+
+static struct pebs_tracer *ds_request_pebs(struct task_struct *task, int cpu,
+                                           void *base, size_t size,
+                                           pebs_ovfl_callback_t ovfl, size_t th,
+                                           unsigned int flags)
 {
         struct pebs_tracer *tracer;
-        unsigned long irq;
         int error;
 
         /* Buffer overflow notification is not yet implemented. */
@@ -753,37 +796,43 @@ struct pebs_tracer *ds_request_pebs(struct task_struct *task,
         if (error < 0)
                 goto out;
 
-        /*
-         * Per-cpu tracing is typically requested using smp_call_function().
-         * We must not sleep.
-         */
         error = -ENOMEM;
-        tracer = kzalloc(sizeof(*tracer), GFP_ATOMIC);
+        tracer = kzalloc(sizeof(*tracer), GFP_KERNEL);
         if (!tracer)
                 goto out_put_tracer;
         tracer->ovfl = ovfl;
 
+        /* Do some more error checking and acquire a tracing context. */
         error = ds_request(&tracer->ds, &tracer->trace.ds,
-                           ds_pebs, task, base, size, th, flags);
+                           ds_pebs, task, cpu, base, size, th);
         if (error < 0)
                 goto out_tracer;
 
-        spin_lock_irqsave(&ds_lock, irq);
+        /* Claim the pebs part of the tracing context we acquired above. */
+        spin_lock_irq(&ds_lock);
 
         error = -EPERM;
         if (tracer->ds.context->pebs_master)
                 goto out_unlock;
         tracer->ds.context->pebs_master = tracer;
 
-        spin_unlock_irqrestore(&ds_lock, irq);
+        spin_unlock_irq(&ds_lock);
 
+        /*
+         * Now that we own the pebs part of the context, let's complete the
+         * initialization for that part.
+         */
+        ds_init_ds_trace(&tracer->trace.ds, ds_pebs, base, size, th, flags);
         ds_write_config(tracer->ds.context, &tracer->trace.ds, ds_pebs);
+        ds_install_ds_area(tracer->ds.context);
+
+        /* Start tracing. */
         ds_resume_pebs(tracer);
 
         return tracer;
 
  out_unlock:
-        spin_unlock_irqrestore(&ds_lock, irq);
+        spin_unlock_irq(&ds_lock);
         ds_put_context(tracer->ds.context);
  out_tracer:
         kfree(tracer);
@@ -793,16 +842,26 @@ struct pebs_tracer *ds_request_pebs(struct task_struct *task,
         return ERR_PTR(error);
 }
 
-void ds_release_bts(struct bts_tracer *tracer)
+struct pebs_tracer *ds_request_pebs_task(struct task_struct *task,
+                                         void *base, size_t size,
+                                         pebs_ovfl_callback_t ovfl,
+                                         size_t th, unsigned int flags)
 {
-        struct task_struct *task;
+        return ds_request_pebs(task, 0, base, size, ovfl, th, flags);
+}
 
-        if (!tracer)
-                return;
+struct pebs_tracer *ds_request_pebs_cpu(int cpu, void *base, size_t size,
+                                        pebs_ovfl_callback_t ovfl,
+                                        size_t th, unsigned int flags)
+{
+        return ds_request_pebs(NULL, cpu, base, size, ovfl, th, flags);
+}
 
-        task = tracer->ds.context->task;
+static void ds_free_bts(struct bts_tracer *tracer)
+{
+        struct task_struct *task;
 
-        ds_suspend_bts(tracer);
+        task = tracer->ds.context->task;
 
         WARN_ON_ONCE(tracer->ds.context->bts_master != tracer);
         tracer->ds.context->bts_master = NULL;
@@ -817,9 +876,69 @@ void ds_release_bts(struct bts_tracer *tracer)
         kfree(tracer);
 }
 
+void ds_release_bts(struct bts_tracer *tracer)
+{
+        might_sleep();
+
+        if (!tracer)
+                return;
+
+        ds_suspend_bts(tracer);
+        ds_free_bts(tracer);
+}
+
+int ds_release_bts_noirq(struct bts_tracer *tracer)
+{
+        struct task_struct *task;
+        unsigned long irq;
+        int error;
+
+        if (!tracer)
+                return 0;
+
+        task = tracer->ds.context->task;
+
+        local_irq_save(irq);
+
+        error = -EPERM;
+        if (!task &&
+            (tracer->ds.context->cpu != smp_processor_id()))
+                goto out;
+
+        error = -EPERM;
+        if (task && (task != current))
+                goto out;
+
+        ds_suspend_bts_noirq(tracer);
+        ds_free_bts(tracer);
+
+        error = 0;
+ out:
+        local_irq_restore(irq);
+        return error;
+}
+
+static void update_task_debugctlmsr(struct task_struct *task,
+                                    unsigned long debugctlmsr)
+{
+        task->thread.debugctlmsr = debugctlmsr;
+
+        get_cpu();
+        if (task == current)
+                update_debugctlmsr(debugctlmsr);
+
+        if (task->thread.debugctlmsr)
+                set_tsk_thread_flag(task, TIF_DEBUGCTLMSR);
+        else
+                clear_tsk_thread_flag(task, TIF_DEBUGCTLMSR);
+        put_cpu();
+}
+
 void ds_suspend_bts(struct bts_tracer *tracer)
 {
         struct task_struct *task;
+        unsigned long debugctlmsr;
+        int cpu;
 
         if (!tracer)
                 return;
@@ -827,29 +946,60 @@ void ds_suspend_bts(struct bts_tracer *tracer)
         tracer->flags = 0;
 
         task = tracer->ds.context->task;
+        cpu  = tracer->ds.context->cpu;
 
-        if (!task || (task == current))
-                update_debugctlmsr(get_debugctlmsr() & ~BTS_CONTROL);
+        WARN_ON(!task && irqs_disabled());
 
-        if (task) {
-                task->thread.debugctlmsr &= ~BTS_CONTROL;
+        debugctlmsr = (task ?
+                       task->thread.debugctlmsr :
+                       get_debugctlmsr_on_cpu(cpu));
+        debugctlmsr &= ~BTS_CONTROL;
 
-                if (!task->thread.debugctlmsr)
-                        clear_tsk_thread_flag(task, TIF_DEBUGCTLMSR);
-        }
+        if (task)
+                update_task_debugctlmsr(task, debugctlmsr);
+        else
+                update_debugctlmsr_on_cpu(cpu, debugctlmsr);
 }
 
-void ds_resume_bts(struct bts_tracer *tracer)
+int ds_suspend_bts_noirq(struct bts_tracer *tracer)
 {
         struct task_struct *task;
-        unsigned long control;
+        unsigned long debugctlmsr, irq;
+        int cpu, error = 0;
 
         if (!tracer)
-                return;
+                return 0;
 
-        tracer->flags = tracer->trace.ds.flags;
+        tracer->flags = 0;
 
         task = tracer->ds.context->task;
+        cpu  = tracer->ds.context->cpu;
+
+        local_irq_save(irq);
+
+        error = -EPERM;
+        if (!task && (cpu != smp_processor_id()))
+                goto out;
+
+        debugctlmsr = (task ?
+                       task->thread.debugctlmsr :
+                       get_debugctlmsr());
+        debugctlmsr &= ~BTS_CONTROL;
+
+        if (task)
+                update_task_debugctlmsr(task, debugctlmsr);
+        else
+                update_debugctlmsr(debugctlmsr);
+
+        error = 0;
+ out:
+        local_irq_restore(irq);
+        return error;
+}
+
+static unsigned long ds_bts_control(struct bts_tracer *tracer)
+{
+        unsigned long control;
 
         control = ds_cfg.ctl[dsf_bts];
         if (!(tracer->trace.ds.flags & BTS_KERNEL))
@@ -857,25 +1007,77 @@ void ds_resume_bts(struct bts_tracer *tracer)
         if (!(tracer->trace.ds.flags & BTS_USER))
                 control |= ds_cfg.ctl[dsf_bts_user];
 
-        if (task) {
-                task->thread.debugctlmsr |= control;
-                set_tsk_thread_flag(task, TIF_DEBUGCTLMSR);
-        }
-
-        if (!task || (task == current))
-                update_debugctlmsr(get_debugctlmsr() | control);
+        return control;
 }
 
-void ds_release_pebs(struct pebs_tracer *tracer)
+void ds_resume_bts(struct bts_tracer *tracer)
 {
         struct task_struct *task;
+        unsigned long debugctlmsr;
+        int cpu;
 
         if (!tracer)
                 return;
 
+        tracer->flags = tracer->trace.ds.flags;
+
         task = tracer->ds.context->task;
+        cpu  = tracer->ds.context->cpu;
 
-        ds_suspend_pebs(tracer);
+        WARN_ON(!task && irqs_disabled());
+
+        debugctlmsr = (task ?
+                       task->thread.debugctlmsr :
+                       get_debugctlmsr_on_cpu(cpu));
+        debugctlmsr |= ds_bts_control(tracer);
+
+        if (task)
+                update_task_debugctlmsr(task, debugctlmsr);
+        else
+                update_debugctlmsr_on_cpu(cpu, debugctlmsr);
+}
+
+int ds_resume_bts_noirq(struct bts_tracer *tracer)
+{
+        struct task_struct *task;
+        unsigned long debugctlmsr, irq;
+        int cpu, error = 0;
+
+        if (!tracer)
+                return 0;
+
+        tracer->flags = tracer->trace.ds.flags;
+
+        task = tracer->ds.context->task;
+        cpu  = tracer->ds.context->cpu;
+
+        local_irq_save(irq);
+
+        error = -EPERM;
+        if (!task && (cpu != smp_processor_id()))
+                goto out;
+
+        debugctlmsr = (task ?
+                       task->thread.debugctlmsr :
+                       get_debugctlmsr());
+        debugctlmsr |= ds_bts_control(tracer);
+
+        if (task)
+                update_task_debugctlmsr(task, debugctlmsr);
+        else
+                update_debugctlmsr(debugctlmsr);
+
+        error = 0;
+ out:
+        local_irq_restore(irq);
+        return error;
+}
+
+static void ds_free_pebs(struct pebs_tracer *tracer)
+{
+        struct task_struct *task;
+
+        task = tracer->ds.context->task;
 
         WARN_ON_ONCE(tracer->ds.context->pebs_master != tracer);
         tracer->ds.context->pebs_master = NULL;
@@ -886,16 +1088,68 @@ void ds_release_pebs(struct pebs_tracer *tracer)
         kfree(tracer);
 }
 
+void ds_release_pebs(struct pebs_tracer *tracer)
+{
+        might_sleep();
+
+        if (!tracer)
+                return;
+
+        ds_suspend_pebs(tracer);
+        ds_free_pebs(tracer);
+}
+
+int ds_release_pebs_noirq(struct pebs_tracer *tracer)
+{
+        struct task_struct *task;
+        unsigned long irq;
+        int error;
+
+        if (!tracer)
+                return 0;
+
+        task = tracer->ds.context->task;
+
+        local_irq_save(irq);
+
+        error = -EPERM;
+        if (!task &&
+            (tracer->ds.context->cpu != smp_processor_id()))
+                goto out;
+
+        error = -EPERM;
+        if (task && (task != current))
+                goto out;
+
+        ds_suspend_pebs_noirq(tracer);
+        ds_free_pebs(tracer);
+
+        error = 0;
+ out:
+        local_irq_restore(irq);
+        return error;
+}
+
 void ds_suspend_pebs(struct pebs_tracer *tracer)
 {
 
 }
 
+int ds_suspend_pebs_noirq(struct pebs_tracer *tracer)
+{
+        return 0;
+}
+
 void ds_resume_pebs(struct pebs_tracer *tracer)
 {
 
 }
 
+int ds_resume_pebs_noirq(struct pebs_tracer *tracer)
+{
+        return 0;
+}
+
 const struct bts_trace *ds_read_bts(struct bts_tracer *tracer)
 {
         if (!tracer)
@@ -1004,26 +1258,6 @@ ds_configure(const struct ds_configuration *cfg,
                 printk(KERN_INFO "[ds] pebs not available\n");
         }
 
-        if (ds_cfg.sizeof_rec[ds_bts]) {
-                int error;
-
-                error = ds_selftest_bts();
-                if (error) {
-                        WARN(1, "[ds] selftest failed. disabling bts.\n");
-                        ds_cfg.sizeof_rec[ds_bts] = 0;
-                }
-        }
-
-        if (ds_cfg.sizeof_rec[ds_pebs]) {
-                int error;
-
-                error = ds_selftest_pebs();
-                if (error) {
-                        WARN(1, "[ds] selftest failed. disabling pebs.\n");
-                        ds_cfg.sizeof_rec[ds_pebs] = 0;
-                }
-        }
-
         printk(KERN_INFO "[ds] sizes: address: %u bit, ",
                8 * ds_cfg.sizeof_ptr_field);
         printk("bts/pebs record: %u/%u bytes\n",
@@ -1127,3 +1361,29 @@ void ds_copy_thread(struct task_struct *tsk, struct task_struct *father)
 void ds_exit_thread(struct task_struct *tsk)
 {
 }
+
+static __init int ds_selftest(void)
+{
+        if (ds_cfg.sizeof_rec[ds_bts]) {
+                int error;
+
+                error = ds_selftest_bts();
+                if (error) {
+                        WARN(1, "[ds] selftest failed. disabling bts.\n");
+                        ds_cfg.sizeof_rec[ds_bts] = 0;
+                }
+        }
+
+        if (ds_cfg.sizeof_rec[ds_pebs]) {
+                int error;
+
+                error = ds_selftest_pebs();
+                if (error) {
+                        WARN(1, "[ds] selftest failed. disabling pebs.\n");
+                        ds_cfg.sizeof_rec[ds_pebs] = 0;
+                }
+        }
+
+        return 0;
+}
+device_initcall(ds_selftest);