From 7f43ef9f0d98abbc0eb5e697628ec06756bf60a9 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Michel=20D=C3=A4nzer?= Date: Wed, 4 Jul 2018 17:14:05 +0200 Subject: [PATCH] dma-buf: Move BUG_ON from _add_shared_fence to _add_shared_inplace MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Fixes the BUG_ON spuriously triggering under the following circumstances: * reservation_object_reserve_shared is called with shared_count == shared_max - 1, so obj->staged is freed in preparation of an in-place update. * reservation_object_add_shared_fence is called with the first fence, after which shared_count == shared_max. * reservation_object_add_shared_fence is called with a follow-up fence from the same context. In the second reservation_object_add_shared_fence call, the BUG_ON triggers. However, nothing bad would happen in reservation_object_add_shared_inplace, since both fences are from the same context, so they only occupy a single slot. Prevent this by moving the BUG_ON to where an overflow would actually happen (e.g. if a buggy caller didn't call reservation_object_reserve_shared before). v2: * Fix description of breaking scenario (Christian König) * Add bugzilla reference Cc: stable@vger.kernel.org Bugzilla: https://bugs.freedesktop.org/106418 Reviewed-by: Chris Wilson # v1 Reviewed-by: Christian König # v1 Signed-off-by: Michel Dänzer Signed-off-by: Sumit Semwal Link: https://patchwork.freedesktop.org/patch/msgid/20180704151405.10357-1-michel@daenzer.net --- drivers/dma-buf/reservation.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c index 20bf90f4ee63..6c95f61a32e7 100644 --- a/drivers/dma-buf/reservation.c +++ b/drivers/dma-buf/reservation.c @@ -141,6 +141,7 @@ reservation_object_add_shared_inplace(struct reservation_object *obj, if (signaled) { RCU_INIT_POINTER(fobj->shared[signaled_idx], fence); } else { + BUG_ON(fobj->shared_count >= fobj->shared_max); RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence); fobj->shared_count++; } @@ -230,10 +231,9 @@ void reservation_object_add_shared_fence(struct reservation_object *obj, old = reservation_object_get_list(obj); obj->staged = NULL; - if (!fobj) { - BUG_ON(old->shared_count >= old->shared_max); + if (!fobj) reservation_object_add_shared_inplace(obj, old, fence); - } else + else reservation_object_add_shared_replace(obj, old, fobj, fence); } EXPORT_SYMBOL(reservation_object_add_shared_fence); -- 2.30.2