Re: [PATCH v2] drm/panic: Fix uninitialized spinlock acquisition with CONFIG_DRM_PANIC=n

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On 17/09/2024 01:00, Lyude Paul wrote:
It turns out that if you happen to have a kernel config where
CONFIG_DRM_PANIC is disabled and spinlock debugging is enabled, along with
KMS being enabled - we'll end up trying to acquire an uninitialized
spin_lock with drm_panic_lock() when we try to do a commit:

The raw spinlock should be initialized in drm_dev_init() [1] regardless of DRM_PANIC being enabled or not.

From the call trace, it looks like you are calling drm_client_register() before calling drm_dev_register(), and that's probably the root cause.

I didn't find a doc saying drm_dev_register() should be done before drm_client_register(), but all drivers are doing it this way.

Can you try to do that in rvkms, and see if it fixes this error ?

Best regards,

--

Jocelyn

[1] https://elixir.bootlin.com/linux/v6.11/source/drivers/gpu/drm/drm_drv.c#L642


   rvkms rvkms.0: [drm:drm_atomic_commit] committing 0000000068d2ade1
   INFO: trying to register non-static key.
   The code is fine but needs lockdep annotation, or maybe
   you didn't initialize this object before use?
   turning off the locking correctness validator.
   CPU: 4 PID: 1347 Comm: modprobe Not tainted 6.10.0-rc1Lyude-Test+ #272
   Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240524-3.fc40 05/24/2024
   Call Trace:
    <TASK>
    dump_stack_lvl+0x77/0xa0
    assign_lock_key+0x114/0x120
    register_lock_class+0xa8/0x2c0
    __lock_acquire+0x7d/0x2bd0
    ? __vmap_pages_range_noflush+0x3a8/0x550
    ? drm_atomic_helper_swap_state+0x2ad/0x3a0
    lock_acquire+0xec/0x290
    ? drm_atomic_helper_swap_state+0x2ad/0x3a0
    ? lock_release+0xee/0x310
    _raw_spin_lock_irqsave+0x4e/0x70
    ? drm_atomic_helper_swap_state+0x2ad/0x3a0
    drm_atomic_helper_swap_state+0x2ad/0x3a0
    drm_atomic_helper_commit+0xb1/0x270
    drm_atomic_commit+0xaf/0xe0
    ? __pfx___drm_printfn_info+0x10/0x10
    drm_client_modeset_commit_atomic+0x1a1/0x250
    drm_client_modeset_commit_locked+0x4b/0x180
    drm_client_modeset_commit+0x27/0x50
    __drm_fb_helper_restore_fbdev_mode_unlocked+0x76/0x90
    drm_fb_helper_set_par+0x38/0x40
    fbcon_init+0x3c4/0x690
    visual_init+0xc0/0x120
    do_bind_con_driver+0x409/0x4c0
    do_take_over_console+0x233/0x280
    do_fb_registered+0x11f/0x210
    fbcon_fb_registered+0x2c/0x60
    register_framebuffer+0x248/0x2a0
    __drm_fb_helper_initial_config_and_unlock+0x58a/0x720
    drm_fbdev_generic_client_hotplug+0x6e/0xb0
    drm_client_register+0x76/0xc0
    _RNvXs_CsHeezP08sTT_5rvkmsNtB4_5RvkmsNtNtCs1cdwasc6FUb_6kernel8platform6Driver5probe+0xed2/0x1060 [rvkms]
    ? _RNvMs_NtCs1cdwasc6FUb_6kernel8platformINtB4_7AdapterNtCsHeezP08sTT_5rvkms5RvkmsE14probe_callbackBQ_+0x2b/0x70 [rvkms]
    ? acpi_dev_pm_attach+0x25/0x110
    ? platform_probe+0x6a/0xa0
    ? really_probe+0x10b/0x400
    ? __driver_probe_device+0x7c/0x140
    ? driver_probe_device+0x22/0x1b0
    ? __device_attach_driver+0x13a/0x1c0
    ? __pfx___device_attach_driver+0x10/0x10
    ? bus_for_each_drv+0x114/0x170
    ? __device_attach+0xd6/0x1b0
    ? bus_probe_device+0x9e/0x120
    ? device_add+0x288/0x4b0
    ? platform_device_add+0x75/0x230
    ? platform_device_register_full+0x141/0x180
    ? rust_helper_platform_device_register_simple+0x85/0xb0
    ? _RNvMs2_NtCs1cdwasc6FUb_6kernel8platformNtB5_6Device13create_simple+0x1d/0x60
    ? _RNvXs0_CsHeezP08sTT_5rvkmsNtB5_5RvkmsNtCs1cdwasc6FUb_6kernel6Module4init+0x11e/0x160 [rvkms]
    ? 0xffffffffc083f000
    ? init_module+0x20/0x1000 [rvkms]
    ? kernfs_xattr_get+0x3e/0x80
    ? do_one_initcall+0x148/0x3f0
    ? __lock_acquire+0x5ef/0x2bd0
    ? __lock_acquire+0x5ef/0x2bd0
    ? __lock_acquire+0x5ef/0x2bd0
    ? put_cpu_partial+0x51/0x1d0
    ? lock_acquire+0xec/0x290
    ? put_cpu_partial+0x51/0x1d0
    ? lock_release+0xee/0x310
    ? put_cpu_partial+0x51/0x1d0
    ? fs_reclaim_acquire+0x69/0xf0
    ? lock_acquire+0xec/0x290
    ? fs_reclaim_acquire+0x69/0xf0
    ? kfree+0x22f/0x340
    ? lock_release+0xee/0x310
    ? kmalloc_trace_noprof+0x48/0x340
    ? do_init_module+0x22/0x240
    ? kmalloc_trace_noprof+0x155/0x340
    ? do_init_module+0x60/0x240
    ? __se_sys_finit_module+0x2e0/0x3f0
    ? do_syscall_64+0xa4/0x180
    ? syscall_exit_to_user_mode+0x108/0x140
    ? do_syscall_64+0xb0/0x180
    ? vma_end_read+0xd0/0xe0
    ? do_user_addr_fault+0x309/0x640
    ? clear_bhb_loop+0x45/0xa0
    ? clear_bhb_loop+0x45/0xa0
    ? clear_bhb_loop+0x45/0xa0
    ? entry_SYSCALL_64_after_hwframe+0x76/0x7e
    </TASK>

Fix this by stubbing these macros out when this config option isn't
enabled, along with fixing the unused variable warning that introduces.

Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Fixes: e2a1cda3e0c7 ("drm/panic: Add drm panic locking")
Cc: <stable@xxxxxxxxxxxxxxx> # v6.10+

---

V2:
* Use static inline instead of macros so we don't need
   __maybe_unused

---
  drivers/gpu/drm/drm_atomic_helper.c |  2 +-
  include/drm/drm_panic.h             | 14 ++++++++++++++
  2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 43cdf39019a44..5186d2114a503 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -3015,7 +3015,7 @@ int drm_atomic_helper_swap_state(struct drm_atomic_state *state,
  				  bool stall)
  {
  	int i, ret;
-	unsigned long flags;
+	unsigned long flags = 0;
  	struct drm_connector *connector;
  	struct drm_connector_state *old_conn_state, *new_conn_state;
  	struct drm_crtc *crtc;
diff --git a/include/drm/drm_panic.h b/include/drm/drm_panic.h
index 54085d5d05c34..f4e1fa9ae607a 100644
--- a/include/drm/drm_panic.h
+++ b/include/drm/drm_panic.h
@@ -64,6 +64,8 @@ struct drm_scanout_buffer {
}; +#ifdef CONFIG_DRM_PANIC
+
  /**
   * drm_panic_trylock - try to enter the panic printing critical section
   * @dev: struct drm_device
@@ -149,4 +151,16 @@ struct drm_scanout_buffer {
  #define drm_panic_unlock(dev, flags) \
  	raw_spin_unlock_irqrestore(&(dev)->mode_config.panic_lock, flags)
+#else
+
+static inline bool drm_panic_trylock(struct drm_device *dev, unsigned long flags)
+{
+	return true;
+}
+
+static inline void drm_panic_lock(struct drm_device *dev, unsigned long flags) {}
+static inline void drm_panic_unlock(struct drm_device *dev, unsigned long flags) {}
+
+#endif
+
  #endif /* __DRM_PANIC_H__ */

base-commit: bf05aeac230e390a5aee4bd3dc978b0c4d7e745f





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