Re: [PATCH] drm/locking: Allow NULL crtc in drm_modeset_legacy_acquire_ctx

["Jasper St. Pierre" <jstpierre@xxxxxxxxxxx>]

This still crashes for me:

kernel: ------------[ cut here ]------------
kernel: WARNING: at drivers/gpu/drm/drm_modeset_lock.c:219 drm_modeset_legacy_acquire_ctx+0x38/0x40()
kernel: Modules linked in:
kernel: CPU: 0 PID: 586 Comm: Xorg Not tainted 3.10.33-02454-g1c4eeb3-dirty #196
kernel: [<c0014c9c>] (unwind_backtrace+0x0/0xec) from [<c0011d34>] (show_stack+0x10/0x14)
kernel: [<c0011d34>] (show_stack+0x10/0x14) from [<c002d2d0>] (warn_slowpath_common+0x54/0x6c)
kernel: [<c002d2d0>] (warn_slowpath_common+0x54/0x6c) from [<c002d384>] (warn_slowpath_null+0x1c/0x24)
kernel: [<c002d384>] (warn_slowpath_null+0x1c/0x24) from [<c02ce818>] (drm_modeset_legacy_acquire_ctx+0x38/0x40)
kernel: [<c02ce818>] (drm_modeset_legacy_acquire_ctx+0x38/0x40) from [<c02afa9c>] (drm_atomic_helper_disable_plane+0x24/0xd0)
kernel: [<c02afa9c>] (drm_atomic_helper_disable_plane+0x24/0xd0) from [<c02c19a4>] (__setplane_internal+0x28/0x2cc)
kernel: [<c02c19a4>] (__setplane_internal+0x28/0x2cc) from [<c02c287c>] (drm_mode_cursor_common+0x1cc/0x2f8)
kernel: [<c02c287c>] (drm_mode_cursor_common+0x1cc/0x2f8) from [<c02c53d4>] (drm_mode_cursor_ioctl+0x58/0x60)
kernel: [<c02c53d4>] (drm_mode_cursor_ioctl+0x58/0x60) from [<c02b917c>] (drm_ioctl+0x318/0x510)
kernel: [<c02b917c>] (drm_ioctl+0x318/0x510) from [<c00e2d9c>] (do_vfs_ioctl+0x55c/0x5b0)
kernel: [<c00e2d9c>] (do_vfs_ioctl+0x55c/0x5b0) from [<c00e2e40>] (SyS_ioctl+0x50/0x7c)
kernel: [<c00e2e40>] (SyS_ioctl+0x50/0x7c) from [<c000e000>] (ret_fast_syscall+0x0/0x30)

This seems to try to acquire the global device lock as instantiated by drm_modeset_lock_all, but nothing in this path calls that. I'm not sure what lock we can acquire when we don't have a CRTC.

On Fri, Nov 21, 2014 at 8:55 AM, Daniel Vetter <daniel.vetter@xxxxxxxx> wrote:

I've missed checking this and so didn't notice that there's a NULL
check missing. Since depending upon calling context the crtc might not
even be there (disable-me-harder does happen around planes, especially
in cleanup code) we need to dodge the oops and look at the global
acquire ctx.

v2: Actually fix the oops for real and don't just move it two lines
down. That requires that we pass a drm_device pointer for the cases
where crtc could be NULL.

Reported-by: "Jasper St. Pierre" <jstpierre@xxxxxxxxxxx>
Cc: "Jasper St. Pierre" <jstpierre@xxxxxxxxxxx>
Cc: Rob Clark <robdclark@xxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
---
 drivers/gpu/drm/drm_atomic_helper.c | 12 ++++++++----
 drivers/gpu/drm/drm_modeset_lock.c  | 12 ++++++++----
 include/drm/drm_modeset_lock.h      |  3 ++-
 3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index ca839bd9bb0d..32c34b5d5f68 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1171,7 +1171,8 @@ int drm_atomic_helper_update_plane(struct drm_plane *plane,
        if (!state)
                return -ENOMEM;

-       state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc);
+       state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc,
+                                                           plane->dev);
 retry:
        plane_state = drm_atomic_get_plane_state(state, plane);
        if (IS_ERR(plane_state)) {
@@ -1239,7 +1240,8 @@ int drm_atomic_helper_disable_plane(struct drm_plane *plane)
        if (!state)
                return -ENOMEM;

-       state->acquire_ctx = drm_modeset_legacy_acquire_ctx(plane->crtc);
+       state->acquire_ctx = drm_modeset_legacy_acquire_ctx(plane->crtc,
+                                                           plane->dev);
 retry:
        plane_state = drm_atomic_get_plane_state(state, plane);
        if (IS_ERR(plane_state)) {
@@ -1391,7 +1393,8 @@ int drm_atomic_helper_set_config(struct drm_mode_set *set)
        if (!state)
                return -ENOMEM;

-       state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc);
+       state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc,
+                                                           crtc->dev);
 retry:
        crtc_state = drm_atomic_get_crtc_state(state, crtc);
        if (IS_ERR(crtc_state)) {
@@ -1676,7 +1679,8 @@ int drm_atomic_helper_page_flip(struct drm_crtc *crtc,
        if (!state)
                return -ENOMEM;

-       state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc);
+       state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc,
+                                                           crtc->dev);
 retry:
        crtc_state = drm_atomic_get_crtc_state(state, crtc);
        if (IS_ERR(crtc_state)) {
diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
index 474e4d12a2d8..655958d4f23e 100644
--- a/drivers/gpu/drm/drm_modeset_lock.c
+++ b/drivers/gpu/drm/drm_modeset_lock.c
@@ -200,21 +200,25 @@ EXPORT_SYMBOL(drm_modeset_lock_crtc);
 /**
  * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
  * @crtc: drm crtc
+ * @dev: device
  *
  * Legacy ioctl operations like cursor updates or page flips only have per-crtc
  * locking, and store the acquire ctx in the corresponding crtc. All other
  * legacy operations take all locks and use a global acquire context. This
  * function grabs the right one.
+ *
+ * Note that either @crtc or @dev can be NULL, but not both.
  */
 struct drm_modeset_acquire_ctx *
-drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
+drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc,
+                              struct drm_device *dev)
 {
-       if (crtc->acquire_ctx)
+       if (crtc && crtc->acquire_ctx)
                return crtc->acquire_ctx;

-       WARN_ON(!crtc->dev->mode_config.acquire_ctx);
+       WARN_ON(!dev->mode_config.acquire_ctx);

-       return crtc->dev->mode_config.acquire_ctx;
+       return dev->mode_config.acquire_ctx;
 }
 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);

diff --git a/include/drm/drm_modeset_lock.h b/include/drm/drm_modeset_lock.h
index 28931a23d96c..cdbfd822e52f 100644
--- a/include/drm/drm_modeset_lock.h
+++ b/include/drm/drm_modeset_lock.h
@@ -135,7 +135,8 @@ void drm_modeset_lock_crtc(struct drm_crtc *crtc);
 void drm_modeset_unlock_crtc(struct drm_crtc *crtc);
 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev);
 struct drm_modeset_acquire_ctx *
-drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc);
+drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc,
+                              struct drm_device *dev);

 int drm_modeset_lock_all_crtcs(struct drm_device *dev,
                struct drm_modeset_acquire_ctx *ctx);
--
2.1.1

--

  Jasper

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