oprofile: warn on freeing event buffer too early
A race shouldn't happen since all workqueues or handlers are canceled
or flushed before the event buffer is freed. A warning is triggered
now if the buffer is freed too early.
Also, this patch adds some comments about event buffer protection,
reworks some code and adds code to clear buffer_pos during alloc and
free of the event buffer.
Cc: David Rientjes <rientjes@google.com>
Cc: Stephane Eranian <eranian@google.com>
Signed-off-by: Robert Richter <robert.richter@amd.com>
diff --git a/drivers/oprofile/event_buffer.c b/drivers/oprofile/event_buffer.c
index c38adb3..5df60a6 100644
--- a/drivers/oprofile/event_buffer.c
+++ b/drivers/oprofile/event_buffer.c
@@ -35,17 +35,22 @@
/* atomic_t because wait_event checks it outside of buffer_mutex */
static atomic_t buffer_ready = ATOMIC_INIT(0);
-/* Add an entry to the event buffer. When we
- * get near to the end we wake up the process
- * sleeping on the read() of the file.
+/*
+ * Add an entry to the event buffer. When we get near to the end we
+ * wake up the process sleeping on the read() of the file. To protect
+ * the event_buffer this function may only be called when buffer_mutex
+ * is set.
*/
void add_event_entry(unsigned long value)
{
/*
- * catch potential error
+ * This shouldn't happen since all workqueues or handlers are
+ * canceled or flushed before the event buffer is freed.
*/
- if (!event_buffer)
+ if (!event_buffer) {
+ WARN_ON_ONCE(1);
return;
+ }
if (buffer_pos == buffer_size) {
atomic_inc(&oprofile_stats.event_lost_overflow);
@@ -75,7 +80,6 @@
int alloc_event_buffer(void)
{
- int err = -ENOMEM;
unsigned long flags;
spin_lock_irqsave(&oprofilefs_lock, flags);
@@ -86,13 +90,12 @@
if (buffer_watershed >= buffer_size)
return -EINVAL;
+ buffer_pos = 0;
event_buffer = vmalloc(sizeof(unsigned long) * buffer_size);
if (!event_buffer)
- goto out;
+ return -ENOMEM;
- err = 0;
-out:
- return err;
+ return 0;
}
@@ -100,6 +103,7 @@
{
mutex_lock(&buffer_mutex);
vfree(event_buffer);
+ buffer_pos = 0;
event_buffer = NULL;
mutex_unlock(&buffer_mutex);
}
@@ -174,6 +178,7 @@
mutex_lock(&buffer_mutex);
+ /* May happen if the buffer is freed during pending reads. */
if (!event_buffer) {
retval = -EINTR;
goto out;