/*
 * Copyright (C) 2012-2014 Canonical Ltd (Maarten Lankhorst)
 *
 * Based on bo.c which bears the following copyright notice,
 * but is dual licensed:
 *
 * Copyright (c) 2006-2009 VMware, Inc., Palo Alto, CA., USA
 * All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sub license, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice (including the
 * next paragraph) shall be included in all copies or substantial portions
 * of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
 * THE COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
 * USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 **************************************************************************/
/*
 * Authors: Thomas Hellstrom <thellstrom-at-vmware-dot-com>
 */

#include <linux/reservation.h>
#include <linux/export.h>

/**
 * DOC: Reservation Object Overview
 *
 * The reservation object provides a mechanism to manage shared and
 * exclusive fences associated with a buffer.  A reservation object
 * can have attached one exclusive fence (normally associated with
 * write operations) or N shared fences (read operations).  The RCU
 * mechanism is used to protect read access to fences from locked
 * write-side updates.
 */

DEFINE_WW_CLASS(reservation_ww_class);
EXPORT_SYMBOL(reservation_ww_class);

struct lock_class_key reservation_seqcount_class;
EXPORT_SYMBOL(reservation_seqcount_class);

const char reservation_seqcount_string[] = "reservation_seqcount";
EXPORT_SYMBOL(reservation_seqcount_string);

/**
 * reservation_object_reserve_shared - Reserve space to add a shared
 * fence to a reservation_object.
 * @obj: reservation object
 *
 * Should be called before reservation_object_add_shared_fence().  Must
 * be called with obj->lock held.
 *
 * RETURNS
 * Zero for success, or -errno
 */
int reservation_object_reserve_shared(struct reservation_object *obj)
{
        struct reservation_object_list *fobj, *old;
        u32 max;

        old = reservation_object_get_list(obj);

        if (old && old->shared_max) {
                if (old->shared_count < old->shared_max) {
                        /* perform an in-place update */
                        kfree(obj->staged);
                        obj->staged = NULL;
                        return 0;
                } else
                        max = old->shared_max * 2;
        } else
                max = 4;

        /*
         * resize obj->staged or allocate if it doesn't exist,
         * noop if already correct size
         */
        fobj = krealloc(obj->staged, offsetof(typeof(*fobj), shared[max]),
                        GFP_KERNEL);
        if (!fobj)
                return -ENOMEM;

        obj->staged = fobj;
        fobj->shared_max = max;
        return 0;
}
EXPORT_SYMBOL(reservation_object_reserve_shared);

static void
reservation_object_add_shared_inplace(struct reservation_object *obj,
                                      struct reservation_object_list *fobj,
                                      struct fence *fence)
{
        u32 i;

        fence_get(fence);

        preempt_disable();
        write_seqcount_begin(&obj->seq);

        for (i = 0; i < fobj->shared_count; ++i) {
                struct fence *old_fence;

                old_fence = rcu_dereference_protected(fobj->shared[i],
                                                reservation_object_held(obj));

                if (old_fence->context == fence->context) {
                        /* memory barrier is added by write_seqcount_begin */
                        RCU_INIT_POINTER(fobj->shared[i], fence);
                        write_seqcount_end(&obj->seq);
                        preempt_enable();

                        fence_put(old_fence);
                        return;
                }
        }

        /*
         * memory barrier is added by write_seqcount_begin,
         * fobj->shared_count is protected by this lock too
         */
        RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence);
        fobj->shared_count++;

        write_seqcount_end(&obj->seq);
        preempt_enable();
}

static void
reservation_object_add_shared_replace(struct reservation_object *obj,
                                      struct reservation_object_list *old,
                                      struct reservation_object_list *fobj,
                                      struct fence *fence)
{
        unsigned i;
        struct fence *old_fence = NULL;

        fence_get(fence);

        if (!old) {
                RCU_INIT_POINTER(fobj->shared[0], fence);
                fobj->shared_count = 1;
                goto done;
        }

        /*
         * no need to bump fence refcounts, rcu_read access
         * requires the use of kref_get_unless_zero, and the
         * references from the old struct are carried over to
         * the new.
         */
        fobj->shared_count = old->shared_count;

        for (i = 0; i < old->shared_count; ++i) {
                struct fence *check;

                check = rcu_dereference_protected(old->shared[i],
                                                reservation_object_held(obj));

                if (!old_fence && check->context == fence->context) {
                        old_fence = check;
                        RCU_INIT_POINTER(fobj->shared[i], fence);
                } else
                        RCU_INIT_POINTER(fobj->shared[i], check);
        }
        if (!old_fence) {
                RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence);
                fobj->shared_count++;
        }

done:
        preempt_disable();
        write_seqcount_begin(&obj->seq);
        /*
         * RCU_INIT_POINTER can be used here,
         * seqcount provides the necessary barriers
         */
        RCU_INIT_POINTER(obj->fence, fobj);
        write_seqcount_end(&obj->seq);
        preempt_enable();

        if (old)
                kfree_rcu(old, rcu);

        if (old_fence)
                fence_put(old_fence);
}

/**
 * reservation_object_add_shared_fence - Add a fence to a shared slot
 * @obj: the reservation object
 * @fence: the shared fence to add
 *
 * Add a fence to a shared slot, obj->lock must be held, and
 * reservation_object_reserve_shared() has been called.
 */
void reservation_object_add_shared_fence(struct reservation_object *obj,
                                         struct fence *fence)
{
        struct reservation_object_list *old, *fobj = obj->staged;

        old = reservation_object_get_list(obj);
        obj->staged = NULL;

        if (!fobj) {
                BUG_ON(old->shared_count >= old->shared_max);
                reservation_object_add_shared_inplace(obj, old, fence);
        } else
                reservation_object_add_shared_replace(obj, old, fobj, fence);
}
EXPORT_SYMBOL(reservation_object_add_shared_fence);

/**
 * reservation_object_add_excl_fence - Add an exclusive fence.
 * @obj: the reservation object
 * @fence: the shared fence to add
 *
 * Add a fence to the exclusive slot.  The obj->lock must be held.
 */
void reservation_object_add_excl_fence(struct reservation_object *obj,
                                       struct fence *fence)
{
        struct fence *old_fence = reservation_object_get_excl(obj);
        struct reservation_object_list *old;
        u32 i = 0;

        old = reservation_object_get_list(obj);
        if (old)
                i = old->shared_count;

        if (fence)
                fence_get(fence);

        preempt_disable();
        write_seqcount_begin(&obj->seq);
        /* write_seqcount_begin provides the necessary memory barrier */
        RCU_INIT_POINTER(obj->fence_excl, fence);
        if (old)
                old->shared_count = 0;
        write_seqcount_end(&obj->seq);
        preempt_enable();

        /* inplace update, no shared fences */
        while (i--)
                fence_put(rcu_dereference_protected(old->shared[i],
                                                reservation_object_held(obj)));

        if (old_fence)
                fence_put(old_fence);
}
EXPORT_SYMBOL(reservation_object_add_excl_fence);

/**
 * reservation_object_get_fences_rcu - Get an object's shared and exclusive
 * fences without update side lock held
 * @obj: the reservation object
 * @pfence_excl: the returned exclusive fence (or NULL)
 * @pshared_count: the number of shared fences returned
 * @pshared: the array of shared fence ptrs returned (array is krealloc'd to
 * the required size, and must be freed by caller)
 *
 * RETURNS
 * Zero or -errno
 */
int reservation_object_get_fences_rcu(struct reservation_object *obj,
                                      struct fence **pfence_excl,
                                      unsigned *pshared_count,
                                      struct fence ***pshared)
{
        unsigned shared_count = 0;
        unsigned retry = 1;
        struct fence **shared = NULL, *fence_excl = NULL;
        int ret = 0;

        while (retry) {
                struct reservation_object_list *fobj;
                unsigned seq;

                seq = read_seqcount_begin(&obj->seq);

                rcu_read_lock();

                fobj = rcu_dereference(obj->fence);
                if (fobj) {
                        struct fence **nshared;
                        size_t sz = sizeof(*shared) * fobj->shared_max;

                        nshared = krealloc(shared, sz,
                                           GFP_NOWAIT | __GFP_NOWARN);
                        if (!nshared) {
                                rcu_read_unlock();
                                nshared = krealloc(shared, sz, GFP_KERNEL);
                                if (nshared) {
                                        shared = nshared;
                                        continue;
                                }

                                ret = -ENOMEM;
                                shared_count = 0;
                                break;
                        }
                        shared = nshared;
                        memcpy(shared, fobj->shared, sz);
                        shared_count = fobj->shared_count;
                } else
                        shared_count = 0;
                fence_excl = rcu_dereference(obj->fence_excl);

                retry = read_seqcount_retry(&obj->seq, seq);
                if (retry)
                        goto unlock;

                if (!fence_excl || fence_get_rcu(fence_excl)) {
                        unsigned i;

                        for (i = 0; i < shared_count; ++i) {
                                if (fence_get_rcu(shared[i]))
                                        continue;

                                /* uh oh, refcount failed, abort and retry */
                                while (i--)
                                        fence_put(shared[i]);

                                if (fence_excl) {
                                        fence_put(fence_excl);
                                        fence_excl = NULL;
                                }

                                retry = 1;
                                break;
                        }
                } else
                        retry = 1;

unlock:
                rcu_read_unlock();
        }
        *pshared_count = shared_count;
        if (shared_count)
                *pshared = shared;
        else {
                *pshared = NULL;
                kfree(shared);
        }
        *pfence_excl = fence_excl;

        return ret;
}
EXPORT_SYMBOL_GPL(reservation_object_get_fences_rcu);

/**
 * reservation_object_wait_timeout_rcu - Wait on reservation's objects
 * shared and/or exclusive fences.
 * @obj: the reservation object
 * @wait_all: if true, wait on all fences, else wait on just exclusive fence
 * @intr: if true, do interruptible wait
 * @timeout: timeout value in jiffies or zero to return immediately
 *
 * RETURNS
 * Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or
 * greater than zer on success.
 */
long reservation_object_wait_timeout_rcu(struct reservation_object *obj,
                                         bool wait_all, bool intr,
                                         unsigned long timeout)
{
        struct fence *fence;
        unsigned seq, shared_count, i = 0;
        long ret = timeout;

        if (!timeout)
                return reservation_object_test_signaled_rcu(obj, wait_all);

retry:
        fence = NULL;
        shared_count = 0;
        seq = read_seqcount_begin(&obj->seq);
        rcu_read_lock();

        if (wait_all) {
                struct reservation_object_list *fobj =
                                                rcu_dereference(obj->fence);

                if (fobj)
                        shared_count = fobj->shared_count;

                if (read_seqcount_retry(&obj->seq, seq))
                        goto unlock_retry;

                for (i = 0; i < shared_count; ++i) {
                        struct fence *lfence = rcu_dereference(fobj->shared[i]);

                        if (test_bit(FENCE_FLAG_SIGNALED_BIT, &lfence->flags))
                                continue;

                        if (!fence_get_rcu(lfence))
                                goto unlock_retry;

                        if (fence_is_signaled(lfence)) {
                                fence_put(lfence);
                                continue;
                        }

                        fence = lfence;
                        break;
                }
        }

        if (!shared_count) {
                struct fence *fence_excl = rcu_dereference(obj->fence_excl);

                if (read_seqcount_retry(&obj->seq, seq))
                        goto unlock_retry;

                if (fence_excl &&
                    !test_bit(FENCE_FLAG_SIGNALED_BIT, &fence_excl->flags)) {
                        if (!fence_get_rcu(fence_excl))
                                goto unlock_retry;

                        if (fence_is_signaled(fence_excl))
                                fence_put(fence_excl);
                        else
                                fence = fence_excl;
                }
        }

        rcu_read_unlock();
        if (fence) {
                ret = fence_wait_timeout(fence, intr, ret);
                fence_put(fence);
                if (ret > 0 && wait_all && (i + 1 < shared_count))
                        goto retry;
        }
        return ret;

unlock_retry:
        rcu_read_unlock();
        goto retry;
}
EXPORT_SYMBOL_GPL(reservation_object_wait_timeout_rcu);


static inline int
reservation_object_test_signaled_single(struct fence *passed_fence)
{
        struct fence *fence, *lfence = passed_fence;
        int ret = 1;

        if (!test_bit(FENCE_FLAG_SIGNALED_BIT, &lfence->flags)) {
                fence = fence_get_rcu(lfence);
                if (!fence)
                        return -1;

                ret = !!fence_is_signaled(fence);
                fence_put(fence);
        }
        return ret;
}

/**
 * reservation_object_test_signaled_rcu - Test if a reservation object's
 * fences have been signaled.
 * @obj: the reservation object
 * @test_all: if true, test all fences, otherwise only test the exclusive
 * fence
 *
 * RETURNS
 * true if all fences signaled, else false
 */
bool reservation_object_test_signaled_rcu(struct reservation_object *obj,
                                          bool test_all)
{
        unsigned seq, shared_count;
        int ret = true;

retry:
        shared_count = 0;
        seq = read_seqcount_begin(&obj->seq);
        rcu_read_lock();

        if (test_all) {
                unsigned i;

                struct reservation_object_list *fobj =
                                                rcu_dereference(obj->fence);

                if (fobj)
                        shared_count = fobj->shared_count;

                if (read_seqcount_retry(&obj->seq, seq))
                        goto unlock_retry;

                for (i = 0; i < shared_count; ++i) {
                        struct fence *fence = rcu_dereference(fobj->shared[i]);

                        ret = reservation_object_test_signaled_single(fence);
                        if (ret < 0)
                                goto unlock_retry;
                        else if (!ret)
                                break;
                }

                /*
                 * There could be a read_seqcount_retry here, but nothing cares
                 * about whether it's the old or newer fence pointers that are
                 * signaled. That race could still have happened after checking
                 * read_seqcount_retry. If you care, use ww_mutex_lock.
                 */
        }

        if (!shared_count) {
                struct fence *fence_excl = rcu_dereference(obj->fence_excl);

                if (read_seqcount_retry(&obj->seq, seq))
                        goto unlock_retry;

                if (fence_excl) {
                        ret = reservation_object_test_signaled_single(
                                                                fence_excl);
                        if (ret < 0)
                                goto unlock_retry;
                }
        }

        rcu_read_unlock();
        return ret;

unlock_retry:
        rcu_read_unlock();
        goto retry;
}
EXPORT_SYMBOL_GPL(reservation_object_test_signaled_rcu);