From: David Rientjes <[email protected]>
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 <[email protected]>
Signed-off-by: Stephane Eranian <[email protected]>
Signed-off-by: Robert Richter <[email protected]>
---
drivers/oprofile/event_buffer.c | 14 +++++++++++++-
1 files changed, 13 insertions(+), 1 deletions(-)
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;
--
1.6.5.rc2
On 09.10.09 21:33:29, Robert Richter wrote:
> From: David Rientjes <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Stephane Eranian <[email protected]>
> Signed-off-by: Robert Richter <[email protected]>
Ingo,
you can also pull the patches from here:
git://git.kernel.org/pub/scm/linux/kernel/git/rric/oprofile.git urgent
Thanks.
-Robert
--
Advanced Micro Devices, Inc.
Operating System Research Center
email: [email protected]
* Robert Richter <[email protected]> wrote:
> On 09.10.09 21:33:29, Robert Richter wrote:
> > From: David Rientjes <[email protected]>
> >
> > 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 <[email protected]>
> > Signed-off-by: Stephane Eranian <[email protected]>
> > Signed-off-by: Robert Richter <[email protected]>
>
> Ingo,
>
> you can also pull the patches from here:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/rric/oprofile.git urgent
>
> Thanks.
Pulled, thanks Robert!
Ingo