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oprofile: warn on freeing event buffer too early

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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>
This commit is contained in:
Robert Richter 2009-10-09 03:17:44 +02:00
parent 066b3aa845
commit c0868934e5
1 changed files with 15 additions and 10 deletions
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25
drivers/oprofile/event_buffer.c
View file

@ -35,17 +35,22 @@ static size_t buffer_pos;
/* atomic_t because wait_event checks it outside of buffer_mutex */ /* atomic_t because wait_event checks it outside of buffer_mutex */
static atomic_t buffer_ready = ATOMIC_INIT(0); 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 * Add an entry to the event buffer. When we get near to the end we
* sleeping on the read() of the file. * 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) 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; return;
}
if (buffer_pos == buffer_size) { if (buffer_pos == buffer_size) {
atomic_inc(&oprofile_stats.event_lost_overflow); atomic_inc(&oprofile_stats.event_lost_overflow);
@ -75,7 +80,6 @@ void wake_up_buffer_waiter(void)
int alloc_event_buffer(void) int alloc_event_buffer(void)
{ {
int err = -ENOMEM;
unsigned long flags; unsigned long flags;
spin_lock_irqsave(&oprofilefs_lock, flags); spin_lock_irqsave(&oprofilefs_lock, flags);
@ -86,13 +90,12 @@ int alloc_event_buffer(void)
if (buffer_watershed >= buffer_size) if (buffer_watershed >= buffer_size)
return -EINVAL; return -EINVAL;
buffer_pos = 0;
event_buffer = vmalloc(sizeof(unsigned long) * buffer_size); event_buffer = vmalloc(sizeof(unsigned long) * buffer_size);
if (!event_buffer) if (!event_buffer)
goto out; return -ENOMEM;
err = 0; return 0;
out:
return err;
} }
@ -100,6 +103,7 @@ void free_event_buffer(void)
{ {
mutex_lock(&buffer_mutex); mutex_lock(&buffer_mutex);
vfree(event_buffer); vfree(event_buffer);
buffer_pos = 0;
event_buffer = NULL; event_buffer = NULL;
mutex_unlock(&buffer_mutex); mutex_unlock(&buffer_mutex);
} }
@ -174,6 +178,7 @@ static ssize_t event_buffer_read(struct file *file, char __user *buf,
mutex_lock(&buffer_mutex); mutex_lock(&buffer_mutex);
/* May happen if the buffer is freed during pending reads. */
if (!event_buffer) { if (!event_buffer) {
retval = -EINTR; retval = -EINTR;
goto out; goto out;