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/*
* Copyright (c) 2017 Richard Braun.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <stddef.h>
#include <stdint.h>
#include <kern/assert.h>
#include <kern/atomic.h>
#include <kern/rtmutex.h>
#include <kern/rtmutex_i.h>
#include <kern/rtmutex_types.h>
#include <kern/thread.h>
#include <kern/turnstile.h>
static void
rtmutex_set_contended(struct rtmutex *rtmutex)
{
atomic_or(&rtmutex->owner, RTMUTEX_CONTENDED, ATOMIC_SEQ_CST);
}
void
rtmutex_lock_slow(struct rtmutex *rtmutex)
{
struct turnstile *turnstile;
uintptr_t owner, prev_owner;
struct thread *thread;
uintptr_t bits;
owner = (uintptr_t)thread_self();
turnstile = turnstile_lend(rtmutex);
rtmutex_set_contended(rtmutex);
bits = RTMUTEX_CONTENDED;
for (;;) {
prev_owner = atomic_cas_seq_cst(&rtmutex->owner, bits, owner | bits);
assert((prev_owner & bits) == bits);
if (prev_owner == bits) {
break;
}
thread = (struct thread *)(prev_owner & RTMUTEX_OWNER_MASK);
turnstile_wait(turnstile, "rtmutex", thread);
bits |= RTMUTEX_FORCE_WAIT;
}
turnstile_own(turnstile);
if (turnstile_empty(turnstile)) {
prev_owner = atomic_swap_seq_cst(&rtmutex->owner, owner);
assert(prev_owner == (owner | bits));
}
turnstile_return(turnstile);
/*
* A lock owner should never perform priority propagation on itself,
* because this process is done using its own priority, potentially
* introducing unbounded priority inversion.
* Instead, let new waiters do it, using their own priority.
*/
}
void
rtmutex_unlock_slow(struct rtmutex *rtmutex)
{
struct turnstile *turnstile;
uintptr_t owner, prev_owner;
owner = (uintptr_t)thread_self();
turnstile = turnstile_acquire(rtmutex);
assert(turnstile != NULL);
prev_owner = atomic_swap_seq_cst(&rtmutex->owner,
RTMUTEX_FORCE_WAIT | RTMUTEX_CONTENDED);
assert((prev_owner & RTMUTEX_OWNER_MASK) == owner);
turnstile_disown(turnstile);
turnstile_signal(turnstile);
turnstile_release(turnstile);
thread_propagate_priority();
}
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