[PATCH v2 09/14] perf, persistent: Protect event lists with mutex

[Robert Richter]

From: Robert Richter <robert.rich...@linaro.org>

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.rich...@linaro.org>
Signed-off-by: Robert Richter <r...@kernel.org>
---
 kernel/events/persistent.c | 33 ++++++++++++++++++++++++---------
 1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/kernel/events/persistent.c b/kernel/events/persistent.c
index 16ed47c..586cea5 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));
 }
 
 /*
@@ -138,28 +148,33 @@ 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;
-       int event_fd;
+       int event_fd = -ENODEV;
 
        if (cpu >= (unsigned)nr_cpu_ids)
                return -EINVAL;
 
+       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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