perf/x86/intel/bts: Fix DS area sharing with x86_pmu events

Currently, the intel_bts driver relies on the DS area allocated by the x86_pmu
code in its event_init() path, which is a bug: creating a BTS event while
no x86_pmu events are present results in a NULL pointer dereference.

The same DS area is also used by PEBS sampling, which makes it quite a bit
trickier to have a separate one for intel_bts' purposes.

This patch makes intel_bts driver use the same DS allocation and reference
counting code as x86_pmu to make sure it is always present when either
intel_bts or x86_pmu need it.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@infradead.org
Cc: adrian.hunter@intel.com
Link: http://lkml.kernel.org/r/1434024837-9916-2-git-send-email-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 4f7001f..aa4e3a7 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -270,11 +270,7 @@ msr_fail:
 
 static void hw_perf_event_destroy(struct perf_event *event)
 {
-       if (atomic_dec_and_mutex_lock(&active_events, &pmc_reserve_mutex)) {
-               release_pmc_hardware();
-               release_ds_buffers();
-               mutex_unlock(&pmc_reserve_mutex);
-       }
+       x86_release_hardware();
 }
 
 void hw_perf_lbr_event_destroy(struct perf_event *event)
@@ -324,6 +320,35 @@ set_ext_hw_attr(struct hw_perf_event *hwc, struct perf_event *event)
        return x86_pmu_extra_regs(val, event);
 }
 
+int x86_reserve_hardware(void)
+{
+       int err = 0;
+
+       if (!atomic_inc_not_zero(&active_events)) {
+               mutex_lock(&pmc_reserve_mutex);
+               if (atomic_read(&active_events) == 0) {
+                       if (!reserve_pmc_hardware())
+                               err = -EBUSY;
+                       else
+                               reserve_ds_buffers();
+               }
+               if (!err)
+                       atomic_inc(&active_events);
+               mutex_unlock(&pmc_reserve_mutex);
+       }
+
+       return err;
+}
+
+void x86_release_hardware(void)
+{
+       if (atomic_dec_and_mutex_lock(&active_events, &pmc_reserve_mutex)) {
+               release_pmc_hardware();
+               release_ds_buffers();
+               mutex_unlock(&pmc_reserve_mutex);
+       }
+}
+
 /*
  * Check if we can create event of a certain type (that no conflicting events
  * are present).
@@ -336,9 +361,10 @@ int x86_add_exclusive(unsigned int what)
                return 0;
 
        mutex_lock(&pmc_reserve_mutex);
-       for (i = 0; i < ARRAY_SIZE(x86_pmu.lbr_exclusive); i++)
+       for (i = 0; i < ARRAY_SIZE(x86_pmu.lbr_exclusive); i++) {
                if (i != what && atomic_read(&x86_pmu.lbr_exclusive[i]))
                        goto out;
+       }
 
        atomic_inc(&x86_pmu.lbr_exclusive[what]);
        ret = 0;
@@ -527,19 +553,7 @@ static int __x86_pmu_event_init(struct perf_event *event)
        if (!x86_pmu_initialized())
                return -ENODEV;
 
-       err = 0;
-       if (!atomic_inc_not_zero(&active_events)) {
-               mutex_lock(&pmc_reserve_mutex);
-               if (atomic_read(&active_events) == 0) {
-                       if (!reserve_pmc_hardware())
-                               err = -EBUSY;
-                       else
-                               reserve_ds_buffers();
-               }
-               if (!err)
-                       atomic_inc(&active_events);
-               mutex_unlock(&pmc_reserve_mutex);
-       }
+       err = x86_reserve_hardware();
        if (err)
                return err;
 

diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
index ef78516..f068695 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -703,6 +703,10 @@ int x86_add_exclusive(unsigned int what);
 
 void x86_del_exclusive(unsigned int what);
 
+int x86_reserve_hardware(void);
+
+void x86_release_hardware(void);
+
 void hw_perf_lbr_event_destroy(struct perf_event *event);
 
 int x86_setup_perfctr(struct perf_event *event);

diff --git a/arch/x86/kernel/cpu/perf_event_intel_bts.c b/arch/x86/kernel/cpu/perf_event_intel_bts.c
index ac1f0c5..7795f3f 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event_intel_bts.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_bts.c
@@ -483,17 +483,26 @@ static int bts_event_add(struct perf_event *event, int mode)
 
 static void bts_event_destroy(struct perf_event *event)
 {
+       x86_release_hardware();
        x86_del_exclusive(x86_lbr_exclusive_bts);
 }
 
 static int bts_event_init(struct perf_event *event)
 {
+       int ret;
+
        if (event->attr.type != bts_pmu.type)
                return -ENOENT;
 
        if (x86_add_exclusive(x86_lbr_exclusive_bts))
                return -EBUSY;
 
+       ret = x86_reserve_hardware();
+       if (ret) {
+               x86_del_exclusive(x86_lbr_exclusive_bts);
+               return ret;
+       }
+
        event->destroy = bts_event_destroy;
 
        return 0;