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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 <ccross@android.com>
Cc: Android Kernel Team <kernel-team@android.com>
Signed-off-by: Alistair Strachan <alistair.strachan@imgtec.com>
[jstultz: minor commit subject tweak]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alistair Strachan 2014-02-04 16:08:36 -08:00 committed by Greg Kroah-Hartman
parent bbd9ae8a05
commit 5cf045f54d
1 changed files with 3 additions and 3 deletions
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6
drivers/staging/android/sync.c
View File

@ -79,13 +79,13 @@ static void sync_timeline_free(struct kref *kref)
container_of(kref, struct sync_timeline, kref); container_of(kref, struct sync_timeline, kref);
unsigned long flags; unsigned long flags;
if (obj->ops->release_obj)
obj->ops->release_obj(obj);
spin_lock_irqsave(&sync_timeline_list_lock, flags); spin_lock_irqsave(&sync_timeline_list_lock, flags);
list_del(&obj->sync_timeline_list); list_del(&obj->sync_timeline_list);
spin_unlock_irqrestore(&sync_timeline_list_lock, flags); spin_unlock_irqrestore(&sync_timeline_list_lock, flags);
if (obj->ops->release_obj)
obj->ops->release_obj(obj);
kfree(obj); kfree(obj);
} }