ClabureDB: Classified Bug-Reports Database

  /*
   * net/tipc/ref.c: TIPC object registry code
   *
   * Copyright (c) 1991-2006, Ericsson AB
   * Copyright (c) 2004-2007, Wind River Systems
   * All rights reserved.
   *
   * 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.
  * 3. Neither the names of the copyright holders nor the names of its
  *    contributors may be used to endorse or promote products derived from
  *    this software without specific prior written permission.
  *
  * Alternatively, this software may be distributed under the terms of the
  * GNU General Public License ("GPL") version 2 as published by the Free
  * Software Foundation.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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 "core.h"
 #include "ref.h"
 
 /**
  * struct reference - TIPC object reference entry
  * @object: pointer to object associated with reference entry
  * @lock: spinlock controlling access to object
  * @ref: reference value for object (combines instance & array index info)
  */
 
 struct reference {
         void *object;
         spinlock_t lock;
         u32 ref;
 };
 
 /**
  * struct tipc_ref_table - table of TIPC object reference entries
  * @entries: pointer to array of reference entries
  * @capacity: array index of first unusable entry
  * @init_point: array index of first uninitialized entry
  * @first_free: array index of first unused object reference entry
  * @last_free: array index of last unused object reference entry
  * @index_mask: bitmask for array index portion of reference values
  * @start_mask: initial value for instance value portion of reference values
  */
 
 struct ref_table {
         struct reference *entries;
         u32 capacity;
         u32 init_point;
         u32 first_free;
         u32 last_free;
         u32 index_mask;
         u32 start_mask;
 };
 
 /*
  * Object reference table consists of 2**N entries.
  *
  * State        Object ptr        Reference
  * -----        ----------      ---------
  * In use        non-NULL       XXXX|own index
  *                                (XXXX changes each time entry is acquired)
  * Free            NULL         YYYY|next free index
  *                                (YYYY is one more than last used XXXX)
  * Uninitialized   NULL         0
  *
  * Entry 0 is not used; this allows index 0 to denote the end of the free list.
  *
  * Note that a reference value of 0 does not necessarily indicate that an
  * entry is uninitialized, since the last entry in the free list could also
  * have a reference value of 0 (although this is unlikely).
  */
 
 static struct ref_table tipc_ref_table = { NULL };
 
 static DEFINE_RWLOCK(ref_table_lock);
 
 /**
  * tipc_ref_table_init - create reference table for objects
  */
 
int tipc_ref_table_init(u32 requested_size, u32 start)
{
        struct reference *table;
        u32 actual_size;

        /* account for unused entry, then round up size to a power of 2 */

        requested_size++;
        for (actual_size = 16; actual_size < requested_size; actual_size <<= 1)
                /* do nothing */ ;

        /* allocate table & mark all entries as uninitialized */

        table = __vmalloc(actual_size * sizeof(struct reference),
                          GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO, PAGE_KERNEL);
        if (table == NULL)
                return -ENOMEM;

        tipc_ref_table.entries = table;
        tipc_ref_table.capacity = requested_size;
        tipc_ref_table.init_point = 1;
        tipc_ref_table.first_free = 0;
        tipc_ref_table.last_free = 0;
        tipc_ref_table.index_mask = actual_size - 1;
        tipc_ref_table.start_mask = start & ~tipc_ref_table.index_mask;

        return 0;
}

/**
 * tipc_ref_table_stop - destroy reference table for objects
 */

void tipc_ref_table_stop(void)
{
        if (!tipc_ref_table.entries)
                return;

        vfree(tipc_ref_table.entries);
        tipc_ref_table.entries = NULL;
}

/**
 * tipc_ref_acquire - create reference to an object
 *
 * Register an object pointer in reference table and lock the object.
 * Returns a unique reference value that is used from then on to retrieve the
 * object pointer, or to determine that the object has been deregistered.
 *
 * Note: The object is returned in the locked state so that the caller can
 * register a partially initialized object, without running the risk that
 * the object will be accessed before initialization is complete.
 */

u32 tipc_ref_acquire(void *object, spinlock_t **lock)
{
        struct reference *entry;
        u32 index;
        u32 index_mask;
        u32 next_plus_upper;
        u32 ref;

        if (!object) {
                err("Attempt to acquire reference to non-existent object\n");
                return 0;
        }
        if (!tipc_ref_table.entries) {
                err("Reference table not found during acquisition attempt\n");
                return 0;
        }

        /* take a free entry, if available; otherwise initialize a new entry */

        write_lock_bh(&ref_table_lock);
        if (tipc_ref_table.first_free) {
                index = tipc_ref_table.first_free;
                entry = &(tipc_ref_table.entries[index]);
                index_mask = tipc_ref_table.index_mask;
                /* take lock in case a previous user of entry still holds it */
                spin_lock_bh(&entry->lock);
                next_plus_upper = entry->ref;
                tipc_ref_table.first_free = next_plus_upper & index_mask;
                ref = (next_plus_upper & ~index_mask) + index;
                entry->ref = ref;
                entry->object = object;
                *lock = &entry->lock;
        }
        else if (tipc_ref_table.init_point < tipc_ref_table.capacity) {
                index = tipc_ref_table.init_point++;
                entry = &(tipc_ref_table.entries[index]);
                spin_lock_init(&entry->lock);
                spin_lock_bh(&entry->lock);
                ref = tipc_ref_table.start_mask + index;
                entry->ref = ref;
                entry->object = object;
                *lock = &entry->lock;
        }
        else {
                ref = 0;
        }
        write_unlock_bh(&ref_table_lock);

        return ref;
}

/**
 * tipc_ref_discard - invalidate references to an object
 *
 * Disallow future references to an object and free up the entry for re-use.
 * Note: The entry's spin_lock may still be busy after discard
 */

void tipc_ref_discard(u32 ref)
{
        struct reference *entry;
        u32 index;
        u32 index_mask;

        if (!tipc_ref_table.entries) {
                err("Reference table not found during discard attempt\n");
                return;
        }

        index_mask = tipc_ref_table.index_mask;
        index = ref & index_mask;
        entry = &(tipc_ref_table.entries[index]);

        write_lock_bh(&ref_table_lock);

        if (!entry->object) {
                err("Attempt to discard reference to non-existent object\n");
                goto exit;
        }
        if (entry->ref != ref) {
                err("Attempt to discard non-existent reference\n");
                goto exit;
        }

        /*
         * mark entry as unused; increment instance part of entry's reference
         * to invalidate any subsequent references
         */

        entry->object = NULL;
        entry->ref = (ref & ~index_mask) + (index_mask + 1);

        /* append entry to free entry list */

        if (tipc_ref_table.first_free == 0)
                tipc_ref_table.first_free = index;
        else
                tipc_ref_table.entries[tipc_ref_table.last_free].ref |= index;
        tipc_ref_table.last_free = index;

exit:
        write_unlock_bh(&ref_table_lock);
}

/**
 * tipc_ref_lock - lock referenced object and return pointer to it
 */

void *tipc_ref_lock(u32 ref)
{
        if (likely(tipc_ref_table.entries)) {
                struct reference *entry;

                entry = &tipc_ref_table.entries[ref &
                                                tipc_ref_table.index_mask];
                if (likely(entry->ref != 0)) {
                        spin_lock_bh(&entry->lock);
                        if (likely((entry->ref == ref) && (entry->object)))
                                return entry->object;
                        spin_unlock_bh(&entry->lock);
                }
        }
        return NULL;
}

/**
 * tipc_ref_unlock - unlock referenced object
 */

void tipc_ref_unlock(u32 ref)
{
        if (likely(tipc_ref_table.entries)) {
                struct reference *entry;

                entry = &tipc_ref_table.entries[ref &
                                                tipc_ref_table.index_mask];
                if (likely((entry->ref == ref) && (entry->object)))
                        spin_unlock_bh(&entry->lock);
                else
                        err("Attempt to unlock non-existent reference\n");
        }
}

/**
 * tipc_ref_deref - return pointer referenced object (without locking it)
 */

void *tipc_ref_deref(u32 ref)
{
        if (likely(tipc_ref_table.entries)) {
                struct reference *entry;

                entry = &tipc_ref_table.entries[ref &
                                                tipc_ref_table.index_mask];
                if (likely(entry->ref == ref))
                        return entry->object;
        }
        return NULL;
}