FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_mutex_obj.c

     /*      $NetBSD: kern_mutex_obj.c,v 1.10 2022/10/26 23:21:19 riastradh Exp $    */
     
     /*-
      * Copyright (c) 2008, 2019 The NetBSD Foundation, Inc.
      * All rights reserved.
      *
      * This code is derived from software contributed to The NetBSD Foundation
      * by Andrew Doran.
      *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     * POSSIBILITY OF SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __KERNEL_RCSID(0, "$NetBSD: kern_mutex_obj.c,v 1.10 2022/10/26 23:21:19 riastradh Exp $");
    
    #include <sys/param.h>
    #include <sys/atomic.h>
    #include <sys/mutex.h>
    #include <sys/pool.h>
    
    /* Mutex cache */
    #define MUTEX_OBJ_MAGIC 0x5aa3c85d
    struct kmutexobj {
            kmutex_t        mo_lock;
            u_int           mo_magic;
            u_int           mo_refcnt;
    };
    
    static int      mutex_obj_ctor(void *, void *, int);
    
    static pool_cache_t     mutex_obj_cache         __read_mostly;
    
    /*
     * mutex_obj_init:
     *
     *      Initialize the mutex object store.
     */
    void
    mutex_obj_init(void)
    {
    
            mutex_obj_cache = pool_cache_init(sizeof(struct kmutexobj),
                coherency_unit, 0, 0, "mutex", NULL, IPL_NONE, mutex_obj_ctor,
                NULL, NULL);
    }
    
    /*
     * mutex_obj_ctor:
     *
     *      Initialize a new lock for the cache.
     */
    static int
    mutex_obj_ctor(void *arg, void *obj, int flags)
    {
            struct kmutexobj * mo = obj;
    
            mo->mo_magic = MUTEX_OBJ_MAGIC;
    
            return 0;
    }
    
    /*
     * mutex_obj_alloc:
     *
     *      Allocate a single lock object, waiting for memory if needed.
     */
    kmutex_t *
    mutex_obj_alloc(kmutex_type_t type, int ipl)
    {
            struct kmutexobj *mo;
    
            mo = pool_cache_get(mutex_obj_cache, PR_WAITOK);
            _mutex_init(&mo->mo_lock, type, ipl,
                (uintptr_t)__builtin_return_address(0));
            mo->mo_refcnt = 1;
    
            return (kmutex_t *)mo;
    }
    
    /*
    * mutex_obj_alloc:
    *
    *      Allocate a single lock object, failing if no memory available.
    */
   kmutex_t *
   mutex_obj_tryalloc(kmutex_type_t type, int ipl)
   {
           struct kmutexobj *mo;
   
           mo = pool_cache_get(mutex_obj_cache, PR_NOWAIT);
           if (__predict_true(mo != NULL)) {
                   _mutex_init(&mo->mo_lock, type, ipl,
                       (uintptr_t)__builtin_return_address(0));
                   mo->mo_refcnt = 1;
           }
   
           return (kmutex_t *)mo;
   }
   
   /*
    * mutex_obj_hold:
    *
    *      Add a single reference to a lock object.  A reference to the object
    *      must already be held, and must be held across this call.
    */
   void
   mutex_obj_hold(kmutex_t *lock)
   {
           struct kmutexobj *mo = (struct kmutexobj *)lock;
   
           KASSERTMSG(mo->mo_magic == MUTEX_OBJ_MAGIC,
               "%s: lock %p: mo->mo_magic (%#x) != MUTEX_OBJ_MAGIC (%#x)",
                __func__, mo, mo->mo_magic, MUTEX_OBJ_MAGIC);
           KASSERTMSG(mo->mo_refcnt > 0,
               "%s: lock %p: mo->mo_refcnt (%#x) == 0",
                __func__, mo, mo->mo_refcnt);
   
           atomic_inc_uint(&mo->mo_refcnt);
   }
   
   /*
    * mutex_obj_free:
    *
    *      Drop a reference from a lock object.  If the last reference is being
    *      dropped, free the object and return true.  Otherwise, return false.
    */
   bool
   mutex_obj_free(kmutex_t *lock)
   {
           struct kmutexobj *mo = (struct kmutexobj *)lock;
   
           KASSERTMSG(mo->mo_magic == MUTEX_OBJ_MAGIC,
               "%s: lock %p: mo->mo_magic (%#x) != MUTEX_OBJ_MAGIC (%#x)",
                __func__, mo, mo->mo_magic, MUTEX_OBJ_MAGIC);
           KASSERTMSG(mo->mo_refcnt > 0,
               "%s: lock %p: mo->mo_refcnt (%#x) == 0",
                __func__, mo, mo->mo_refcnt);
   
   #ifndef __HAVE_ATOMIC_AS_MEMBAR
           membar_release();
   #endif
           if (atomic_dec_uint_nv(&mo->mo_refcnt) > 0) {
                   return false;
           }
   #ifndef __HAVE_ATOMIC_AS_MEMBAR
           membar_acquire();
   #endif
           mutex_destroy(&mo->mo_lock);
           pool_cache_put(mutex_obj_cache, mo);
           return true;
   }
   
   /*
    * mutex_obj_refcnt:
    *
    *      Return the reference count on a lock object.
    */
   u_int
   mutex_obj_refcnt(kmutex_t *lock)
   {
           struct kmutexobj *mo = (struct kmutexobj *)lock;
   
           return mo->mo_refcnt;
   }

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