Re: [PATCH] rust: mutex: fix __mutex_init() usage in case of PREEMPT_RT

[Conor Dooley <conor@kernel.org>]

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On Mon, Sep 16, 2024 at 09:37:52AM +0200, Dirk Behme wrote:
> In case CONFIG_PREEMPT_RT is enabled __mutex_init() becomes a macro
> instead of an extern function (simplified from
> include/linux/mutex.h):
> 
> extern void __mutex_init(struct mutex *lock, const char *name,
> 			 struct lock_class_key *key);
> do {							\
> 	rt_mutex_base_init(&(mutex)->rtmutex);		\
> 	__mutex_rt_init((mutex), name, key);		\
> } while (0)
> 
> The macro isn't resolved by bindgen, then. What results in a build
> error:
> 
> error[E0425]: cannot find function `__mutex_init` in crate `bindings`
>      --> rust/kernel/sync/lock/mutex.rs:104:28
>       |
> 104   |           unsafe { bindings::__mutex_init(ptr, name, key) }
>       |                              ^^^^^^^^^^^^ help: a function with a similar name exists: `__mutex_rt_init`
>       |
>      ::: rust/bindings/bindings_generated.rs:23722:5
>       |
> 23722 | /     pub fn __mutex_rt_init(
> 23723 | |         lock: *mut mutex,
> 23724 | |         name: *const core::ffi::c_char,
> 23725 | |         key: *mut lock_class_key,
> 23726 | |     );
>       | |_____- similarly named function `__mutex_rt_init` defined here
> 
> Fix this by adding a helper.
> 
> As explained by Gary Guo in [1] no #ifdef CONFIG_PREEMPT_RT
> is needed here as rust/bindings/lib.rs prefers externed function to
> helpers if an externed function exists.
> 
> Reported-by: Conor Dooley <conor@kernel.org>

Welp, once I turned off the 7 or so lock debugging config options again,
it does seem that this patch has solved the PREEMPT_RT related build
breakage - thanks.
Tested-by: Conor Dooley <conor.dooley@microchip.com>

Cheers,
Conor.

> Link: https://lore.kernel.org/rust-for-linux/20240913-shack-estate-b376a65921b1@spud/
> Link: https://lore.kernel.org/rust-for-linux/20240915123626.1a170103.gary@garyguo.net/ [1]
> Fixes: 6d20d629c6d8 ("rust: lock: introduce `Mutex`")
> Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>

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