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>

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index db843f812a607bd75e24058ca197255310140d29..eb346048f00f5beaa1fb1439543db0ae3445672f 100644 (file)
--- 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);