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[92.176.231.205]) by smtp.gmail.com with ESMTPSA id y25-20020a7bcd99000000b003fc04eb92cbsm140379wmj.44.2023.07.17.09.30.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Jul 2023 09:30:32 -0700 (PDT) From: Javier Martinez Canillas To: linux-kernel@vger.kernel.org Cc: Thomas Zimmermann , Daniel Vetter , Javier Martinez Canillas , Geert Uytterhoeven , Daniel Vetter , David Airlie , dri-devel@lists.freedesktop.org Subject: [PATCH v3] drm/ssd130x: Fix an oops when attempting to update a disabled plane Date: Mon, 17 Jul 2023 18:30:22 +0200 Message-ID: <20230717163027.480918-1-javierm@redhat.com> X-Mailer: git-send-email 2.41.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Geert reports that the following NULL pointer dereference happens for him after commit 49d7d581ceaf ("drm/ssd130x: Don't allocate buffers on each plane update"): [drm] Initialized ssd130x 1.0.0 20220131 for 0-003c on minor 0 ssd130x-i2c 0-003c: [drm] surface width(128), height(32), bpp(1) and format(R1 little-endian (0x20203152)) Unable to handle kernel NULL pointer dereference at virtual address 000= 00000 Oops [#1] CPU: 0 PID: 1 Comm: swapper Not tainted 6.5.0-rc1-orangecrab-02219-g0a529a1e4bf4 #565 epc : ssd130x_update_rect.isra.0+0x13c/0x340 ra : ssd130x_update_rect.isra.0+0x2bc/0x340 ... status: 00000120 badaddr: 00000000 cause: 0000000f [] ssd130x_update_rect.isra.0+0x13c/0x340 [] ssd130x_primary_plane_helper_atomic_update+0x26c/0x284 [] drm_atomic_helper_commit_planes+0xfc/0x27c [] drm_atomic_helper_commit_tail+0x5c/0xb4 [] commit_tail+0x190/0x1b8 [] drm_atomic_helper_commit+0x194/0x1c0 [] drm_atomic_commit+0xa4/0xe4 [] drm_client_modeset_commit_atomic+0x244/0x278 [] drm_client_modeset_commit_locked+0x7c/0x1bc [] drm_client_modeset_commit+0x34/0x64 [] __drm_fb_helper_restore_fbdev_mode_unlocked+0xc4/0xe8 [] drm_fb_helper_set_par+0x38/0x58 [] fbcon_init+0x294/0x534 ... The problem is that fbcon calls fbcon_init() which triggers a DRM modeset and this leads to drm_atomic_helper_commit_planes() attempting to commit the atomic state for all planes, even the ones whose CRTC is not enabled. Since the primary plane buffer is allocated in the encoder .atomic_enable callback, this happens after that initial modeset commit and leads to the mentioned NULL pointer dereference. Fix this by allocating the buffers in the struct drm_plane_helper_funcs .begin_fb_access callback and free them in to .end_fb_access callback, instead of doing it when the encoder is enabled. Fixes: 49d7d581ceaf ("drm/ssd130x: Don't allocate buffers on each plane upd= ate") Reported-by: Geert Uytterhoeven Signed-off-by: Javier Martinez Canillas --- Changes in v3: - Move the buffers allocation to the plane helper funcs .begin_fb_access and the free to .end_fb_access callbacks. - Always allocate intermediate buffer because is use in ssd130x_clear_scree= n(). - Don't allocate the buffers as device managed resources. Changes in v2: - Move the buffers allocation to .fb_create instead of preventing atomic updates for disable planes. - Don't allocate the intermediate buffer when using the native R1 format. - Allocate buffers as device managed resources. drivers/gpu/drm/solomon/ssd130x.c | 33 ++++++++++++++++++++++++------- 1 file changed, 26 insertions(+), 7 deletions(-) diff --git a/drivers/gpu/drm/solomon/ssd130x.c b/drivers/gpu/drm/solomon/ss= d130x.c index afb08a8aa9fc..be68b63200a0 100644 --- a/drivers/gpu/drm/solomon/ssd130x.c +++ b/drivers/gpu/drm/solomon/ssd130x.c @@ -612,6 +612,30 @@ static int ssd130x_fb_blit_rect(struct drm_framebuffer= *fb, const struct iosys_m return ret; } =20 +static int ssd130x_primary_plane_helper_begin_fb_access(struct drm_plane *= plane, + struct drm_plane_state *state) +{ + struct drm_device *drm =3D plane->dev; + struct ssd130x_device *ssd130x =3D drm_to_ssd130x(drm); + int ret =3D ssd130x_buf_alloc(ssd130x); + + if (ret) + return ret; + + return drm_gem_begin_shadow_fb_access(plane, state); +} + +static void ssd130x_primary_plane_helper_end_fb_access(struct drm_plane *p= lane, + struct drm_plane_state *state) +{ + struct drm_device *drm =3D plane->dev; + struct ssd130x_device *ssd130x =3D drm_to_ssd130x(drm); + + ssd130x_buf_free(ssd130x); + + return drm_gem_end_shadow_fb_access(plane, state); +} + static void ssd130x_primary_plane_helper_atomic_update(struct drm_plane *p= lane, struct drm_atomic_state *state) { @@ -656,7 +680,8 @@ static void ssd130x_primary_plane_helper_atomic_disable= (struct drm_plane *plane, } =20 static const struct drm_plane_helper_funcs ssd130x_primary_plane_helper_fu= ncs =3D { - DRM_GEM_SHADOW_PLANE_HELPER_FUNCS, + .begin_fb_access =3D ssd130x_primary_plane_helper_begin_fb_access, + .end_fb_access =3D ssd130x_primary_plane_helper_end_fb_access, .atomic_check =3D drm_plane_helper_atomic_check, .atomic_update =3D ssd130x_primary_plane_helper_atomic_update, .atomic_disable =3D ssd130x_primary_plane_helper_atomic_disable, @@ -719,10 +744,6 @@ static void ssd130x_encoder_helper_atomic_enable(struc= t drm_encoder *encoder, if (ret) goto power_off; =20 - ret =3D ssd130x_buf_alloc(ssd130x); - if (ret) - goto power_off; - ssd130x_write_cmd(ssd130x, 1, SSD130X_DISPLAY_ON); =20 backlight_enable(ssd130x->bl_dev); @@ -744,8 +765,6 @@ static void ssd130x_encoder_helper_atomic_disable(struc= t drm_encoder *encoder, =20 ssd130x_write_cmd(ssd130x, 1, SSD130X_DISPLAY_OFF); =20 - ssd130x_buf_free(ssd130x); - ssd130x_power_off(ssd130x); } =20 --=20 2.41.0