perf_counter: Fix cpuctx->task_ctx races

Peter noticed that we are sometimes reading cpuctx->task_ctx with
interrupts enabled.

Noticed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 20 insertions, 8 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index db843f812a60..eb346048f00f 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -234,15 +234,18 @@ static void __perf_counter_remove_from_context(void *info)
         struct perf_counter_context *ctx = counter->ctx;
         unsigned long flags;
 
+        local_irq_save(flags);
         /*
          * If this is a task context, we need to check whether it is
          * the current task context of this cpu. If not it has been
          * scheduled out before the smp call arrived.
          */
-        if (ctx->task && cpuctx->task_ctx != ctx)
+        if (ctx->task && cpuctx->task_ctx != ctx) {
+                local_irq_restore(flags);
                 return;
+        }
 
-        spin_lock_irqsave(&ctx->lock, flags);
+        spin_lock(&ctx->lock);
         /*
          * Protect the list operation against NMI by disabling the
          * counters on a global level.
@@ -382,14 +385,17 @@ static void __perf_counter_disable(void *info)
         struct perf_counter_context *ctx = counter->ctx;
         unsigned long flags;
 
+        local_irq_save(flags);
         /*
          * If this is a per-task counter, need to check whether this
          * counter's task is the current task on this cpu.
          */
-        if (ctx->task && cpuctx->task_ctx != ctx)
+        if (ctx->task && cpuctx->task_ctx != ctx) {
+                local_irq_restore(flags);
                 return;
+        }
 
-        spin_lock_irqsave(&ctx->lock, flags);
+        spin_lock(&ctx->lock);
 
         /*
          * If the counter is on, turn it off.
@@ -615,6 +621,7 @@ static void __perf_install_in_context(void *info)
         unsigned long flags;
         int err;
 
+        local_irq_save(flags);
         /*
          * If this is a task context, we need to check whether it is
          * the current task context of this cpu. If not it has been
@@ -623,12 +630,14 @@ static void __perf_install_in_context(void *info)
          * on this cpu because it had no counters.
          */
         if (ctx->task && cpuctx->task_ctx != ctx) {
-                if (cpuctx->task_ctx || ctx->task != current)
+                if (cpuctx->task_ctx || ctx->task != current) {
+                        local_irq_restore(flags);
                         return;
+                }
                 cpuctx->task_ctx = ctx;
         }
 
-        spin_lock_irqsave(&ctx->lock, flags);
+        spin_lock(&ctx->lock);
         ctx->is_active = 1;
         update_context_time(ctx);
 
@@ -745,17 +754,20 @@ static void __perf_counter_enable(void *info)
         unsigned long flags;
         int err;
 
+        local_irq_save(flags);
         /*
          * If this is a per-task counter, need to check whether this
          * counter's task is the current task on this cpu.
          */
         if (ctx->task && cpuctx->task_ctx != ctx) {
-                if (cpuctx->task_ctx || ctx->task != current)
+                if (cpuctx->task_ctx || ctx->task != current) {
+                        local_irq_restore(flags);
                         return;
+                }
                 cpuctx->task_ctx = ctx;
         }
 
-        spin_lock_irqsave(&ctx->lock, flags);
+        spin_lock(&ctx->lock);
         ctx->is_active = 1;
         update_context_time(ctx);