linux-kernel - Re: [PATCH 19/50] locking/mutex: split out mutex

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Date: Mon, 18 Dec 2023 13:12:46 -0500
From: Waiman Long <longman@...hat.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-fsdevel@...r.kernel.org
Cc: tglx@...utronix.de, x86@...nel.org, tj@...nel.org, peterz@...radead.org,
 mathieu.desnoyers@...icios.com, paulmck@...nel.org, keescook@...omium.org,
 dave.hansen@...ux.intel.com, mingo@...hat.com, will@...nel.org,
 boqun.feng@...il.com, brauner@...nel.org
Subject: Re: [PATCH 19/50] locking/mutex: split out mutex_types.h

On 12/15/23 22:26, Kent Overstreet wrote:
> Trimming down sched.h dependencies: we don't want to include more than
> the base types.
>
> Signed-off-by: Kent Overstreet<kent.overstreet@...ux.dev>
> Cc: Peter Zijlstra<peterz@...radead.org>
> Cc: Ingo Molnar<mingo@...hat.com>
> Cc: Will Deacon<will@...nel.org>
> Cc: Waiman Long<longman@...hat.com>
> Cc: Boqun Feng<boqun.feng@...il.com>
> Signed-off-by: Kent Overstreet<kent.overstreet@...ux.dev>
> ---
>   include/linux/mutex.h       | 52 +--------------------------
>   include/linux/mutex_types.h | 71 +++++++++++++++++++++++++++++++++++++
>   include/linux/sched.h       |  2 +-
>   3 files changed, 73 insertions(+), 52 deletions(-)
>   create mode 100644 include/linux/mutex_types.h
>
> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> index a33aa9eb9fc3..0dfba5df6524 100644
> --- a/include/linux/mutex.h
> +++ b/include/linux/mutex.h
> @@ -20,6 +20,7 @@
>   #include <linux/osq_lock.h>
>   #include <linux/debug_locks.h>
>   #include <linux/cleanup.h>
> +#include <linux/mutex_types.h>
>   
>   #ifdef CONFIG_DEBUG_LOCK_ALLOC
>   # define __DEP_MAP_MUTEX_INITIALIZER(lockname)			\
> @@ -33,49 +34,6 @@
>   
>   #ifndef CONFIG_PREEMPT_RT
>   
> -/*
> - * Simple, straightforward mutexes with strict semantics:
> - *
> - * - only one task can hold the mutex at a time
> - * - only the owner can unlock the mutex
> - * - multiple unlocks are not permitted
> - * - recursive locking is not permitted
> - * - a mutex object must be initialized via the API
> - * - a mutex object must not be initialized via memset or copying
> - * - task may not exit with mutex held
> - * - memory areas where held locks reside must not be freed
> - * - held mutexes must not be reinitialized
> - * - mutexes may not be used in hardware or software interrupt
> - *   contexts such as tasklets and timers
> - *
> - * These semantics are fully enforced when DEBUG_MUTEXES is
> - * enabled. Furthermore, besides enforcing the above rules, the mutex
> - * debugging code also implements a number of additional features
> - * that make lock debugging easier and faster:
> - *
> - * - uses symbolic names of mutexes, whenever they are printed in debug output
> - * - point-of-acquire tracking, symbolic lookup of function names
> - * - list of all locks held in the system, printout of them
> - * - owner tracking
> - * - detects self-recursing locks and prints out all relevant info
> - * - detects multi-task circular deadlocks and prints out all affected
> - *   locks and tasks (and only those tasks)
> - */
> -struct mutex {
> -	atomic_long_t		owner;
> -	raw_spinlock_t		wait_lock;
> -#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
> -	struct optimistic_spin_queue osq; /* Spinner MCS lock */
> -#endif
> -	struct list_head	wait_list;
> -#ifdef CONFIG_DEBUG_MUTEXES
> -	void			*magic;
> -#endif
> -#ifdef CONFIG_DEBUG_LOCK_ALLOC
> -	struct lockdep_map	dep_map;
> -#endif
> -};
> -
>   #ifdef CONFIG_DEBUG_MUTEXES
>   
>   #define __DEBUG_MUTEX_INITIALIZER(lockname)				\
> @@ -131,14 +89,6 @@ extern bool mutex_is_locked(struct mutex *lock);
>   /*
>    * Preempt-RT variant based on rtmutexes.
>    */
> -#include <linux/rtmutex.h>

Including rtmutex.h here means that mutex_types.h is no longer a simple 
header for types only. So unless you also break out a rtmutex_types.h, 
it is inconsistent.

Besides, the kernel/sched code does use mutex_lock/unlock calls quite 
frequently. With this patch, mutex.h will not be directly included. I 
suspect that it is indirectly included via other header files. This may 
be an issue with some configurations.

Cheers, Longman