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Subject[PATCH 11/16] perf, persistent: Protect event lists with mutex
Date
From: Robert Richter <robert.richter@calxeda.com>

Protect esp. access to struct pers_event_desc *desc. There are race
conditions possible where the descriptor could be removed from list
while it is used.

Signed-off-by: Robert Richter <robert.richter@calxeda.com>
---
kernel/events/persistent.c | 36 ++++++++++++++++++++++++++----------
1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/kernel/events/persistent.c b/kernel/events/persistent.c
index 4ecbdab..ebef089 100644
--- a/kernel/events/persistent.c
+++ b/kernel/events/persistent.c
@@ -15,6 +15,7 @@ struct pers_event_desc {
};

static DEFINE_PER_CPU(struct list_head, pers_events);
+static DEFINE_PER_CPU(struct mutex, pers_events_lock);

static struct pers_event_desc
*get_persistent_event(int cpu, struct perf_event_attr *attr)
@@ -37,9 +38,13 @@ add_persistent_event_on_cpu(unsigned int cpu, struct perf_event_attr *attr,
struct pers_event_desc *desc;
struct ring_buffer *buf;

+ mutex_lock(&per_cpu(pers_events_lock, cpu));
+
desc = kzalloc(sizeof(*desc), GFP_KERNEL);
- if (!desc)
- return ERR_PTR(-ENOMEM);
+ if (!desc) {
+ event = ERR_PTR(-ENOMEM);
+ goto out;
+ }

event = perf_event_create_kernel_counter(attr, cpu, NULL, NULL, NULL);
if (IS_ERR(event))
@@ -66,6 +71,7 @@ err_rb:
err_event:
kfree(desc);
out:
+ mutex_unlock(&per_cpu(pers_events_lock, cpu));
return event;
}

@@ -74,9 +80,11 @@ static void del_persistent_event(int cpu, struct perf_event_attr *attr)
struct pers_event_desc *desc;
struct perf_event *event;

+ mutex_lock(&per_cpu(pers_events_lock, cpu));
+
desc = get_persistent_event(cpu, attr);
if (!desc)
- return;
+ goto out;
event = desc->event;

list_del(&desc->plist);
@@ -85,6 +93,8 @@ static void del_persistent_event(int cpu, struct perf_event_attr *attr)
perf_event_release_kernel(event);
put_unused_fd(desc->fd);
kfree(desc);
+out:
+ mutex_unlock(&per_cpu(pers_events_lock, cpu));
}

/*
@@ -137,25 +147,31 @@ int perf_add_persistent_event_by_id(int id)

int perf_get_persistent_event_fd(unsigned cpu, struct perf_event_attr *attr)
{
- struct pers_event_desc *desc = get_persistent_event(cpu, attr);
- int event_fd;
+ struct pers_event_desc *desc;
+ int event_fd = -ENODEV;

+ mutex_lock(&per_cpu(pers_events_lock, cpu));
+
+ desc = get_persistent_event(cpu, attr);
if (!desc)
- return -ENODEV;
+ goto out;

event_fd = anon_inode_getfd("[pers_event]", &perf_fops,
desc->event, O_RDONLY);
if (event_fd >= 0)
desc->fd = event_fd;
+out:
+ mutex_unlock(&per_cpu(pers_events_lock, cpu));

return event_fd;
}

-
void __init persistent_events_init(void)
{
- int i;
+ int cpu;

- for_each_possible_cpu(i)
- INIT_LIST_HEAD(&per_cpu(pers_events, i));
+ for_each_possible_cpu(cpu) {
+ INIT_LIST_HEAD(&per_cpu(pers_events, cpu));
+ mutex_init(&per_cpu(pers_events_lock, cpu));
+ }
}
--
1.8.1.1


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