From 5bfd40139d55790cbc8e56ad1ce4f974f1fa186d Mon Sep 17 00:00:00 2001 From: Boris Brezillon Date: Wed, 22 Nov 2017 21:39:28 +0100 Subject: [PATCH] drm/vc4: Fix false positive WARN() backtrace on refcount_inc() usage With CONFIG_REFCOUNT_FULL enabled, refcount_inc() complains when it's passed a refcount object that has its counter set to 0. In this driver, this is a valid use case since we want to increment ->usecnt only when the BO object starts to be used by real HW components and this is definitely not the case when the BO is created. Fix the problem by using refcount_inc_not_zero() instead of refcount_inc() and fallback to refcount_set(1) when refcount_inc_not_zero() returns false. Note that this 2-steps operation is not racy here because the whole section is protected by a mutex which guarantees that the counter does not change between the refcount_inc_not_zero() and refcount_set() calls. Fixes: b9f19259b84d ("drm/vc4: Add the DRM_IOCTL_VC4_GEM_MADVISE ioctl") Reported-by: Stefan Wahren Signed-off-by: Boris Brezillon Acked-by: Eric Anholt Link: https://patchwork.freedesktop.org/patch/msgid/20171122203928.28135-1-boris.brezillon@free-electrons.com --- drivers/gpu/drm/vc4/vc4_bo.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/vc4/vc4_bo.c b/drivers/gpu/drm/vc4/vc4_bo.c index 4ae45d7dac42..2decc8e2c79f 100644 --- a/drivers/gpu/drm/vc4/vc4_bo.c +++ b/drivers/gpu/drm/vc4/vc4_bo.c @@ -637,7 +637,8 @@ int vc4_bo_inc_usecnt(struct vc4_bo *bo) mutex_lock(&bo->madv_lock); switch (bo->madv) { case VC4_MADV_WILLNEED: - refcount_inc(&bo->usecnt); + if (!refcount_inc_not_zero(&bo->usecnt)) + refcount_set(&bo->usecnt, 1); ret = 0; break; case VC4_MADV_DONTNEED: