drm/i915: properly init lockdep class

The code has an ifdef and uses two functions to either init the bare spinlock or init it and set a lock-class. It is possible to do the same thing without an ifdef.
With this patch (in debug case) we first use the "default" lock class which is later overwritten to the supplied one. Without lockdep the set name/class function vanishes.

Reported-by kbuild test robot <[email protected]>

+++ b/drivers/gpu/drm/i915/i915_gem_timeline.c

drivers/gpu/drm/i915/i915_gem_timeline.c +1 -4

@@ -33,11 +33,8 @@ static void __intel_timeline_init(struct
 {
 	tl->fence_context = context;
 	tl->common = parent;
-#ifdef CONFIG_DEBUG_SPINLOCK
-	__raw_spin_lock_init(&tl->lock.rlock, lockname, lockclass);
-#else
 	spin_lock_init(&tl->lock);
-#endif
+	lockdep_set_class_and_name(&tl->lock, lockclass, lockname);
 	init_request_active(&tl->last_request, NULL);
 	INIT_LIST_HEAD(&tl->requests);
 	i915_syncmap_init(&tl->sync);

Quoted 8 lines · Sebastian Andrzej Siewior

The code has an ifdef and uses two functions to either init the bare spinlock or init it and set a lock-class. It is possible to do the same thing without an ifdef.
With this patch (in debug case) we first use the "default" lock class which is later overwritten to the supplied one. Without lockdep the set name/class function vanishes.

Reported-by kbuild test robot <[email protected]>

How exactly did kbuild test robot figure this out?

At least according to the source there doesn't seem to be clarity about what is the right thing to do, this being just one option.

Regards, Joonas

Quoted 8 lines · Joonas Lahtinen

Quoted 7 lines · Sebastian Andrzej Siewior

The code has an ifdef and uses two functions to either init the bare spinlock or init it and set a lock-class. It is possible to do the same thing without an ifdef.
With this patch (in debug case) we first use the "default" lock class which is later overwritten to the supplied one. Without lockdep the set name/class function vanishes.

Quoted 3 lines

Quoted 1 line

Reported-by kbuild test robot <[email protected]>

How exactly did kbuild test robot figure this out?

I fixed it up for RT, then robot found a way to complain about it. Then I slapped myself for not submitting this patch in the first place.

Quoted 2 lines

At least according to the source there doesn't seem to be clarity about what is the right thing to do, this being just one option.

I don' think `ifdef CONFIG_DEBUG_SPINLOCK' is an option. Especially since the i915 driver here is the only user in tree doing this kind of thing.
Then we have lockdep_set_class_and_name() (which I promote here). This looks like the official way of doing lockdep related things and it has even more than ten users in tree.

Quoted 8 lines · Sebastian Andrzej Siewior

Quoted 7 lines · Joonas Lahtinen

Quoted 6 lines · Sebastian Andrzej Siewior

The code has an ifdef and uses two functions to either init the bare spinlock or init it and set a lock-class. It is possible to do the same thing without an ifdef.
With this patch (in debug case) we first use the "default" lock class which is later overwritten to the supplied one. Without lockdep the set name/class function vanishes.

Quoted 9 lines

Quoted 2 lines

At least according to the source there doesn't seem to be clarity about what is the right thing to do, this being just one option.

I don' think `ifdef CONFIG_DEBUG_SPINLOCK' is an option. Especially since the i915 driver here is the only user in tree doing this kind of thing.
Then we have lockdep_set_class_and_name() (which I promote here). This looks like the official way of doing lockdep related things and it has even more than ten users in tree.

I think it be worthwhile to suggest would be the addition of __spin_lock_init where you can pass in the the lockclass and name.

Regards, Joonas

+peterz
context: http://www.spinics.net/lists/intel-gfx/msg149011.html

Quoted 2 lines · Joonas Lahtinen

Quoted 1 line · Sebastian Andrzej Siewior

On 2017-12-13 16:00:49 [+0200], Joonas Lahtinen wrote:

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Quoted 7 lines · Sebastian Andrzej Siewior

Quoted 6 lines

The code has an ifdef and uses two functions to either init the bare spinlock or init it and set a lock-class. It is possible to do the same thing without an ifdef.
With this patch (in debug case) we first use the "default" lock class which is later overwritten to the supplied one. Without lockdep the set name/class function vanishes.

…

Quoted 2 lines

Quoted 2 lines

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At least according to the source there doesn't seem to be clarity about what is the right thing to do, this being just one option.