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42 lines
1.8 KiB
Diff
42 lines
1.8 KiB
Diff
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From 5537bac0e5c8f3634c5595c21c7d63f0c0263e0e Mon Sep 17 00:00:00 2001
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From: Boris Brezillon <boris.brezillon@free-electrons.com>
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Date: Wed, 22 Nov 2017 21:39:28 +0100
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Subject: [PATCH 175/454] drm/vc4: Fix false positive WARN() backtrace on
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refcount_inc() usage
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With CONFIG_REFCOUNT_FULL enabled, refcount_inc() complains when it's
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passed a refcount object that has its counter set to 0. In this driver,
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this is a valid use case since we want to increment ->usecnt only when
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the BO object starts to be used by real HW components and this is
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definitely not the case when the BO is created.
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Fix the problem by using refcount_inc_not_zero() instead of
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refcount_inc() and fallback to refcount_set(1) when
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refcount_inc_not_zero() returns false. Note that this 2-steps operation
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is not racy here because the whole section is protected by a mutex
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which guarantees that the counter does not change between the
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refcount_inc_not_zero() and refcount_set() calls.
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Fixes: b9f19259b84d ("drm/vc4: Add the DRM_IOCTL_VC4_GEM_MADVISE ioctl")
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Reported-by: Stefan Wahren <stefan.wahren@i2se.com>
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Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
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Acked-by: Eric Anholt <eric@anholt.net>
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Link: https://patchwork.freedesktop.org/patch/msgid/20171122203928.28135-1-boris.brezillon@free-electrons.com
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(cherry picked from commit 5bfd40139d55790cbc8e56ad1ce4f974f1fa186d)
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---
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drivers/gpu/drm/vc4/vc4_bo.c | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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--- a/drivers/gpu/drm/vc4/vc4_bo.c
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+++ b/drivers/gpu/drm/vc4/vc4_bo.c
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@@ -639,7 +639,8 @@ int vc4_bo_inc_usecnt(struct vc4_bo *bo)
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mutex_lock(&bo->madv_lock);
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switch (bo->madv) {
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case VC4_MADV_WILLNEED:
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- refcount_inc(&bo->usecnt);
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+ if (!refcount_inc_not_zero(&bo->usecnt))
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+ refcount_set(&bo->usecnt, 1);
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ret = 0;
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break;
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case VC4_MADV_DONTNEED:
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