From: Alistair Strachan Date: Wed, 5 Feb 2014 00:08:36 +0000 (-0800) Subject: staging: sync: Fix a race condition between release_obj and print_obj X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=5cf045f54d31894ec59ee741e01fa258be2ba0fb;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git staging: 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. Cc: Colin Cross Cc: Android Kernel Team Signed-off-by: Alistair Strachan [jstultz: minor commit subject tweak] Signed-off-by: John Stultz Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c index 38e5d3b5ed9b..b7fcaab0acea 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); }