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Date: Thu, 22 May 2025 15:09:43 +0100
From: Catalin Marinas <catalin.marinas@arm.com>
To: Maxime Ripard <mripard@kernel.org>
Cc: Dave Stevenson <dave.stevenson@raspberrypi.com>,
	=?iso-8859-1?Q?Ma=EDra?= Canal <mcanal@igalia.com>,
	Raspberry Pi Kernel Maintenance <kernel-list@raspberrypi.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>, Simona Vetter <simona@ffwll.ch>,
	Dmitry Baryshkov <lumag@kernel.org>,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/vc4: tests: pv_muxing: Fix locking
Message-ID: <aC8wJ9EbkB0x5AUP@arm.com>
References: <20250520-drm-vc4-kunit-fixes-v1-1-ca281e485f8e@kernel.org>
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In-Reply-To: <20250520-drm-vc4-kunit-fixes-v1-1-ca281e485f8e@kernel.org>

On Tue, May 20, 2025 at 02:08:36PM +0200, Maxime Ripard wrote:
> Commit 30188df0c387 ("drm/tests: Drop drm_kunit_helper_acquire_ctx_alloc()")
> removed a kunit-managed function to get a drm_modeset_acquire_ctx.
> 
> It converted the vc4_pv_muxing_test_init() function, used by
> drm_vc4_test_pv_muxing() and drm_vc4_test_pv_muxing_invalid(). However,
> during that conversion, it went from being kzalloc'd to being allocated
> on the stack.
> 
> vc4_pv_muxing_test_init() then uses that context to allocate a
> drm_atomic_state using drm_kunit_helper_atomic_state_alloc(), which
> stores a pointer to the locking context in the allocated state.
> 
> However, since vc4_pv_muxing_test_init() is a test init function, the
> context is then cleared when we leave the function, and before executing
> the test. We're then running the test with a dangling pointer, which
> then leads to various crashes.
> 
> Rework the context initialization and state allocation to move them to
> drm_vc4_test_pv_muxing() and drm_vc4_test_pv_muxing_invalid().
> 
> Fixes: 30188df0c387 ("drm/tests: Drop drm_kunit_helper_acquire_ctx_alloc()")
> Reported-by: Catalin Marinas <catalin.marinas@arm.com>
> Closes: https://lore.kernel.org/r/Z_95jWM2YMTGy3pi@arm.com/
> Signed-off-by: Maxime Ripard <mripard@kernel.org>

FWIW, I no longer get the kernel panic:

Tested-by: Catalin Marinas <catalin.marinas@arm.com>