The following commit has been merged in the linux branch: commit 066b3aa8454bee3cdc665d86b5de812d8d0513b3 Author: David Rientjes rientjes@google.com Date: Wed Sep 9 15:02:33 2009 +0200

oprofile: fix race condition in event_buffer free

Looking at the 2.6.31-rc9 code, it appears there is a race condition in the event_buffer cleanup code path (shutdown). This could lead to kernel panic as some CPUs may be operating on the event buffer AFTER it has been freed. The attached patch solves the problem and makes sure CPUs check if the buffer is not NULL before they access it as some may have been spinning on the mutex while the buffer was being freed.

The race may happen if the buffer is freed during pending reads. But it is not clear why there are races in add_event_entry() since all workqueues or handlers are canceled or flushed before the event buffer is freed.

Signed-off-by: David Rientjes rientjes@google.com Signed-off-by: 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 2b7ae36..c38adb3 100644 --- a/drivers/oprofile/event_buffer.c +++ b/drivers/oprofile/event_buffer.c @@ -41,6 +41,12 @@ static atomic_t buffer_ready = ATOMIC_INIT(0); */ void add_event_entry(unsigned long value) { + /* + * catch potential error + */ + if (!event_buffer) + return; + if (buffer_pos == buffer_size) { atomic_inc(&oprofile_stats.event_lost_overflow); return; @@ -92,9 +98,10 @@ out:

void free_event_buffer(void) { + mutex_lock(&buffer_mutex); vfree(event_buffer); - event_buffer = NULL; + mutex_unlock(&buffer_mutex); }

@@ -167,6 +174,11 @@ static ssize_t event_buffer_read(struct file *file, char __user *buf,

mutex_lock(&buffer_mutex);

+ if (!event_buffer) { + retval = -EINTR; + goto out; + } + atomic_set(&buffer_ready, 0);

retval = -EFAULT;