Messages in this thread Patch in this message | | | Date | Tue, 13 Jul 2021 17:11:27 +0200 | From | Thomas Gleixner <> | Subject | [patch 33/50] locking/mutex: Introduce _mutex_t |
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From: Thomas Gleixner <tglx@linutronix.de>
PREEMPT_RT replaces 'struct mutex' with a rtmutex based variant so all mutex operations are included into the priority inheritance scheme.
But a complete replacement of the mutex implementation would require to reimplement ww_mutex on top of the rtmutex based variant. That has been tried, but the outcome was suboptimal.
As ww_mutex is mostly used in DRM and the code pathes are not really relevant to typical RT applications, it's also hard to argue for a full reimplementation which can't even share code with the regular ww_mutex code adding the risk of diversion and different bugs in both code bases.
The alternative solution is to make it possible to compile the ww_mutex specific part of the regular mutex implementation as is on RT and have a rtmutex based 'struct mutex' variant.
As the regular mutex and ww_mutex implementation are tightly coupled (ww_mutex has a 'struct mutex' inside) and share a lot of code (ww_mutex is mostly an extension) a simple replacement of 'struct mutex' does not work.
To solve this attach a typedef to 'struct mutex': _mutex_t
This new type is then used to replace 'struct mutex' in 'struct ww_mutex', in a few helper functions and in the actual regular mutex code. None of the actual usage sites of mutexes are affected.
That allows in the final step to have a RT specific 'struct mutex' and the regular _mutex_t type.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- include/linux/mutex.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) --- diff --git a/include/linux/mutex.h b/include/linux/mutex.h index 0bbc872ba72b..87dafe179ed2 100644 --- a/include/linux/mutex.h +++ b/include/linux/mutex.h @@ -48,7 +48,13 @@ * - detects multi-task circular deadlocks and prints out all affected * locks and tasks (and only those tasks) */ -struct mutex { + +/* + * Typedef _mutex_t for ww_mutex and core code to allow ww_mutex being + * built on the regular mutex code in RT kernels while mutex itself is + * substituted by a rt_mutex. + */ +typedef struct mutex { atomic_long_t owner; raw_spinlock_t wait_lock; #ifdef CONFIG_MUTEX_SPIN_ON_OWNER @@ -61,7 +67,7 @@ struct mutex { #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif -}; +} _mutex_t; #ifdef CONFIG_DEBUG_MUTEXES
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