From: Alistair Strachan Date: Wed, 10 Apr 2013 23:35:14 +0000 (-0700) Subject: sync: Fix a race condition between release_obj and print_obj X-Git-Tag: firefly_0821_release~4090^2~493 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=637dd81343b2019938cf6307f75bb7c934a99fc2;p=firefly-linux-kernel-4.4.55.git sync: Fix a race condition between release_obj and print_obj Before this change, a timeline would only be removed from the timeline list *after* the sync driver had its release_obj() called. However, the driver's release_obj() may free resources needed by print_obj(). Although the timeline list is locked when print_obj() is called, it is not locked when release_obj() is called. If one CPU was in print_obj() when another was in release_obj(), the print_obj() may make unsafe accesses. It is not actually necessary to hold the timeline list lock when calling release_obj() if the call is made after the timeline is unlinked from the list, since there is no possibility another thread could be in -- or enter -- print_obj() for that timeline. This change moves the release_obj() call to after the timeline is unlinked, preventing the above race from occurring. Signed-off-by: Alistair Strachan (cherry picked from commit 3bfc1e9e0c7d0c0e3f52ee1f3803482416afa295) Change-Id: Ib2b2b23fde5be34016f9d86b8b9c5e561b56cd4c --- diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c index c5a43934e855..d38305b40930 100644 --- a/drivers/staging/android/sync.c +++ b/drivers/staging/android/sync.c @@ -79,13 +79,13 @@ static void sync_timeline_free(struct kref *kref) container_of(kref, struct sync_timeline, kref); unsigned long flags; - if (obj->ops->release_obj) - obj->ops->release_obj(obj); - spin_lock_irqsave(&sync_timeline_list_lock, flags); list_del(&obj->sync_timeline_list); spin_unlock_irqrestore(&sync_timeline_list_lock, flags); + if (obj->ops->release_obj) + obj->ops->release_obj(obj); + kfree(obj); }