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 00000000
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
[<c0303d90>] ssd130x_update_rect.isra.0+0x13c/0x340
[<c0304200>] ssd130x_primary_plane_helper_atomic_update+0x26c/0x284
[<c02f8d54>] drm_atomic_helper_commit_planes+0xfc/0x27c
[<c02f9314>] drm_atomic_helper_commit_tail+0x5c/0xb4
[<c02f94fc>] commit_tail+0x190/0x1b8
[<c02f99fc>] drm_atomic_helper_commit+0x194/0x1c0
[<c02c5d00>] drm_atomic_commit+0xa4/0xe4
[<c02cce40>] drm_client_modeset_commit_atomic+0x244/0x278
[<c02ccef0>] drm_client_modeset_commit_locked+0x7c/0x1bc
[<c02cd064>] drm_client_modeset_commit+0x34/0x64
[<c0301a78>] __drm_fb_helper_restore_fbdev_mode_unlocked+0xc4/0xe8
[<c0303424>] drm_fb_helper_set_par+0x38/0x58
[<c027c410>] 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 update")
Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
---
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_screen().
- 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/ssd130x.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;
}
+static int ssd130x_primary_plane_helper_begin_fb_access(struct drm_plane *plane,
+ struct drm_plane_state *state)
+{
+ struct drm_device *drm = plane->dev;
+ struct ssd130x_device *ssd130x = drm_to_ssd130x(drm);
+ int ret = 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 *plane,
+ struct drm_plane_state *state)
+{
+ struct drm_device *drm = plane->dev;
+ struct ssd130x_device *ssd130x = 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 *plane,
struct drm_atomic_state *state)
{
@@ -656,7 +680,8 @@ static void ssd130x_primary_plane_helper_atomic_disable(struct drm_plane *plane,
}
static const struct drm_plane_helper_funcs ssd130x_primary_plane_helper_funcs = {
- DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
+ .begin_fb_access = ssd130x_primary_plane_helper_begin_fb_access,
+ .end_fb_access = ssd130x_primary_plane_helper_end_fb_access,
.atomic_check = drm_plane_helper_atomic_check,
.atomic_update = ssd130x_primary_plane_helper_atomic_update,
.atomic_disable = ssd130x_primary_plane_helper_atomic_disable,
@@ -719,10 +744,6 @@ static void ssd130x_encoder_helper_atomic_enable(struct drm_encoder *encoder,
if (ret)
goto power_off;
- ret = ssd130x_buf_alloc(ssd130x);
- if (ret)
- goto power_off;
-
ssd130x_write_cmd(ssd130x, 1, SSD130X_DISPLAY_ON);
backlight_enable(ssd130x->bl_dev);
@@ -744,8 +765,6 @@ static void ssd130x_encoder_helper_atomic_disable(struct drm_encoder *encoder,
ssd130x_write_cmd(ssd130x, 1, SSD130X_DISPLAY_OFF);
- ssd130x_buf_free(ssd130x);
-
ssd130x_power_off(ssd130x);
}
--
2.41.0
