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Subject[PATCH 2/7] perf_counter: sanitize counter->mutex
s/counter->mutex/counter->child_mutex/ and make sure its only used to protect
child_list.

The usage in __perf_counter_exit_task() doesn't appear to be problematic
since ctx->mutex also covers anything related to fd tear-down.

LKML-Reference: <new-submission>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
include/linux/perf_counter.h | 7 ++----
kernel/perf_counter.c | 47 +++++++++++++++++--------------------------
2 files changed, 22 insertions(+), 32 deletions(-)
Index: linux-2.6/include/linux/perf_counter.h
===================================================================
--- linux-2.6.orig/include/linux/perf_counter.h
+++ linux-2.6/include/linux/perf_counter.h
@@ -452,9 +452,6 @@ struct perf_counter {
struct perf_counter_context *ctx;
struct file *filp;

- struct perf_counter *parent;
- struct list_head child_list;
-
/*
* These accumulate total time (in nanoseconds) that children
* counters have been enabled and running, respectively.
@@ -465,7 +462,9 @@ struct perf_counter {
/*
* Protect attach/detach and child_list:
*/
- struct mutex mutex;
+ struct mutex child_mutex;
+ struct list_head child_list;
+ struct perf_counter *parent;

int oncpu;
int cpu;
Index: linux-2.6/kernel/perf_counter.c
===================================================================
--- linux-2.6.orig/kernel/perf_counter.c
+++ linux-2.6/kernel/perf_counter.c
@@ -111,6 +111,10 @@ static void put_ctx(struct perf_counter_
}
}

+/*
+ * Add a counter from the lists for its context.
+ * Must be called with ctx->mutex and ctx->lock held.
+ */
static void
list_add_counter(struct perf_counter *counter, struct perf_counter_context *ctx)
{
@@ -136,7 +140,7 @@ list_add_counter(struct perf_counter *co

/*
* Remove a counter from the lists for its context.
- * Must be called with counter->mutex and ctx->mutex held.
+ * Must be called with ctx->mutex and ctx->lock held.
*/
static void
list_del_counter(struct perf_counter *counter, struct perf_counter_context *ctx)
@@ -276,7 +280,7 @@ static void __perf_counter_remove_from_c
/*
* Remove the counter from a task's (or a CPU's) list of counters.
*
- * Must be called with counter->mutex and ctx->mutex held.
+ * Must be called with ctx->mutex held.
*
* CPU counters are removed with a smp call. For task counters we only
* call when the task is on a CPU.
@@ -1407,11 +1411,7 @@ static int perf_release(struct inode *in
file->private_data = NULL;

mutex_lock(&ctx->mutex);
- mutex_lock(&counter->mutex);
-
perf_counter_remove_from_context(counter);
-
- mutex_unlock(&counter->mutex);
mutex_unlock(&ctx->mutex);

free_counter(counter);
@@ -1437,7 +1437,7 @@ perf_read_hw(struct perf_counter *counte
if (counter->state == PERF_COUNTER_STATE_ERROR)
return 0;

- mutex_lock(&counter->mutex);
+ mutex_lock(&counter->child_mutex);
values[0] = perf_counter_read(counter);
n = 1;
if (counter->hw_event.read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
@@ -1446,7 +1446,7 @@ perf_read_hw(struct perf_counter *counte
if (counter->hw_event.read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
values[n++] = counter->total_time_running +
atomic64_read(&counter->child_total_time_running);
- mutex_unlock(&counter->mutex);
+ mutex_unlock(&counter->child_mutex);

if (count < n * sizeof(u64))
return -EINVAL;
@@ -1510,11 +1510,11 @@ static void perf_counter_for_each_child(
{
struct perf_counter *child;

- mutex_lock(&counter->mutex);
+ mutex_lock(&counter->child_mutex);
func(counter);
list_for_each_entry(child, &counter->child_list, child_list)
func(child);
- mutex_unlock(&counter->mutex);
+ mutex_unlock(&counter->child_mutex);
}

static void perf_counter_for_each(struct perf_counter *counter,
@@ -1522,11 +1522,11 @@ static void perf_counter_for_each(struct
{
struct perf_counter *child;

- mutex_lock(&counter->mutex);
+ mutex_lock(&counter->child_mutex);
perf_counter_for_each_sibling(counter, func);
list_for_each_entry(child, &counter->child_list, child_list)
perf_counter_for_each_sibling(child, func);
- mutex_unlock(&counter->mutex);
+ mutex_unlock(&counter->child_mutex);
}

static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
@@ -3106,7 +3106,9 @@ perf_counter_alloc(struct perf_counter_h
if (!group_leader)
group_leader = counter;

- mutex_init(&counter->mutex);
+ mutex_init(&counter->child_mutex);
+ INIT_LIST_HEAD(&counter->child_list);
+
INIT_LIST_HEAD(&counter->list_entry);
INIT_LIST_HEAD(&counter->event_entry);
INIT_LIST_HEAD(&counter->sibling_list);
@@ -3114,8 +3116,6 @@ perf_counter_alloc(struct perf_counter_h

mutex_init(&counter->mmap_mutex);

- INIT_LIST_HEAD(&counter->child_list);
-
counter->cpu = cpu;
counter->hw_event = *hw_event;
counter->group_leader = group_leader;
@@ -3346,10 +3346,9 @@ inherit_counter(struct perf_counter *par
/*
* Link this into the parent counter's child list
*/
- mutex_lock(&parent_counter->mutex);
+ mutex_lock(&parent_counter->child_mutex);
list_add_tail(&child_counter->child_list, &parent_counter->child_list);
-
- mutex_unlock(&parent_counter->mutex);
+ mutex_unlock(&parent_counter->child_mutex);

return child_counter;
}
@@ -3396,9 +3395,9 @@ static void sync_child_counter(struct pe
/*
* Remove this counter from the parent's list
*/
- mutex_lock(&parent_counter->mutex);
+ mutex_lock(&parent_counter->child_mutex);
list_del_init(&child_counter->child_list);
- mutex_unlock(&parent_counter->mutex);
+ mutex_unlock(&parent_counter->child_mutex);

/*
* Release the parent counter, if this was the last
@@ -3414,17 +3413,9 @@ __perf_counter_exit_task(struct task_str
{
struct perf_counter *parent_counter;

- /*
- * Protect against concurrent operations on child_counter
- * due its fd getting closed, etc.
- */
- mutex_lock(&child_counter->mutex);
-
update_counter_times(child_counter);
list_del_counter(child_counter, child_ctx);

- mutex_unlock(&child_counter->mutex);
-
parent_counter = child_counter->parent;
/*
* It can happen that parent exits first, and has counters
--



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