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Subject[[PATCH v6 07/10] perf: Add return value for perf_event_read().
Date
When we implement the ability to read several counters at once (using
the PERF_PMU_TXN_READ transaction interface), perf_event_read() can
fail when the 'group' parameter is true (eg: trying to read too many
events at once).

For now, have perf_event_read() return an integer. Ignore the return
value when the 'group' parameter is false.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---
kernel/events/core.c | 45 ++++++++++++++++++++++++++++++++++-----------
1 file changed, 34 insertions(+), 11 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2c38c09..acdd8b5 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3187,6 +3187,7 @@ void perf_event_exec(void)
struct perf_read_data {
struct perf_event *event;
bool group;
+ int ret;
};

/*
@@ -3227,6 +3228,7 @@ static void __perf_event_read(void *info)
if (sub->state == PERF_EVENT_STATE_ACTIVE)
sub->pmu->read(sub);
}
+ data->ret = 0;

unlock:
raw_spin_unlock(&ctx->lock);
@@ -3293,8 +3295,10 @@ u64 perf_event_read_local(struct perf_event *event)
return val;
}

-static void perf_event_read(struct perf_event *event, bool group)
+static int perf_event_read(struct perf_event *event, bool group)
{
+ int ret = 0;
+
/*
* If event is enabled and currently active on a CPU, update the
* value in the event structure:
@@ -3303,9 +3307,11 @@ static void perf_event_read(struct perf_event *event, bool group)
struct perf_read_data data = {
.event = event,
.group = group,
+ .ret = 0,
};
smp_call_function_single(event->oncpu,
__perf_event_read, &data, 1);
+ ret = data.ret;
} else if (event->state == PERF_EVENT_STATE_INACTIVE) {
struct perf_event_context *ctx = event->ctx;
unsigned long flags;
@@ -3326,6 +3332,8 @@ static void perf_event_read(struct perf_event *event, bool group)
update_event_times(event);
raw_spin_unlock_irqrestore(&ctx->lock, flags);
}
+
+ return ret;
}

/*
@@ -3842,7 +3850,7 @@ u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)

mutex_lock(&event->child_mutex);

- perf_event_read(event, false);
+ (void)perf_event_read(event, false);
total += perf_event_count(event);

*enabled += event->total_time_enabled +
@@ -3851,7 +3859,7 @@ u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
atomic64_read(&event->child_total_time_running);

list_for_each_entry(child, &event->child_list, child_list) {
- perf_event_read(child, false);
+ (void)perf_event_read(child, false);
total += perf_event_count(child);
*enabled += child->total_time_enabled;
*running += child->total_time_running;
@@ -3862,13 +3870,16 @@ u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
}
EXPORT_SYMBOL_GPL(perf_event_read_value);

-static void __perf_read_group_add(struct perf_event *leader,
+static int __perf_read_group_add(struct perf_event *leader,
u64 read_format, u64 *values)
{
struct perf_event *sub;
int n = 1; /* skip @nr */
+ int ret;

- perf_event_read(leader, true);
+ ret = perf_event_read(leader, true);
+ if (ret)
+ return ret;

/*
* Since we co-schedule groups, {enabled,running} times of siblings
@@ -3897,6 +3908,8 @@ static void __perf_read_group_add(struct perf_event *leader,
if (read_format & PERF_FORMAT_ID)
values[n++] = primary_event_id(sub);
}
+
+ return 0;
}

static int perf_read_group(struct perf_event *event,
@@ -3904,7 +3917,7 @@ static int perf_read_group(struct perf_event *event,
{
struct perf_event *leader = event->group_leader, *child;
struct perf_event_context *ctx = leader->ctx;
- int ret = event->read_size;
+ int ret;
u64 *values;

lockdep_assert_held(&ctx->mutex);
@@ -3921,17 +3934,27 @@ static int perf_read_group(struct perf_event *event,
*/
mutex_lock(&leader->child_mutex);

- __perf_read_group_add(leader, read_format, values);
- list_for_each_entry(child, &leader->child_list, child_list)
- __perf_read_group_add(child, read_format, values);
+ ret = __perf_read_group_add(leader, read_format, values);
+ if (ret)
+ goto unlock;
+
+ list_for_each_entry(child, &leader->child_list, child_list) {
+ ret = __perf_read_group_add(child, read_format, values);
+ if (ret)
+ goto unlock;
+ }

mutex_unlock(&leader->child_mutex);

+ ret = event->read_size;
if (copy_to_user(buf, values, event->read_size))
ret = -EFAULT;
+ goto out;

+unlock:
+ mutex_unlock(&leader->child_mutex);
+out:
kfree(values);
-
return ret;
}

@@ -4037,7 +4060,7 @@ static unsigned int perf_poll(struct file *file, poll_table *wait)

static void _perf_event_reset(struct perf_event *event)
{
- perf_event_read(event, false);
+ (void)perf_event_read(event, false);
local64_set(&event->count, 0);
perf_event_update_userpage(event);
}
--
1.7.9.5


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