[akaros.git] / kern / src / kthread.c

/* Copyright (c) 2010-13 The Regents of the University of California
 * Barret Rhoden <brho@cs.berkeley.edu>
 * See LICENSE for details.
 *
 * Kernel threading.  These are for blocking within the kernel for whatever
 * reason, usually during blocking IO operations. */

#include <kthread.h>
#include <slab.h>
#include <page_alloc.h>
#include <pmap.h>
#include <smp.h>
#include <schedule.h>

uintptr_t get_kstack(void)
{
        uintptr_t stackbot;
        if (KSTKSIZE == PGSIZE)
                stackbot = (uintptr_t)kpage_alloc_addr();
        else
                stackbot = (uintptr_t)get_cont_pages(KSTKSHIFT >> PGSHIFT, 0);
        assert(stackbot);
        return stackbot + KSTKSIZE;
}

void put_kstack(uintptr_t stacktop)
{
        uintptr_t stackbot = stacktop - KSTKSIZE;
        if (KSTKSIZE == PGSIZE)
                page_decref(kva2page((void*)stackbot));
        else
                free_cont_pages((void*)stackbot, KSTKSHIFT >> PGSHIFT);
}

uintptr_t *kstack_bottom_addr(uintptr_t stacktop)
{
        /* canary at the bottom of the stack */
        assert(!PGOFF(stacktop));
        return (uintptr_t*)(stacktop - KSTKSIZE);
}

struct kmem_cache *kthread_kcache;

void kthread_init(void)
{
        kthread_kcache = kmem_cache_create("kthread", sizeof(struct kthread),
                                           __alignof__(struct kthread), 0, 0, 0);
}

/* Used by early init routines (smp_boot, etc) */
struct kthread *__kthread_zalloc(void)
{
        struct kthread *kthread;
        kthread = kmem_cache_alloc(kthread_kcache, 0);
        assert(kthread);
        memset(kthread, 0, sizeof(struct kthread));
        return kthread;
}

/* Starts kthread on the calling core.  This does not return, and will handle
 * the details of cleaning up whatever is currently running (freeing its stack,
 * etc).  Pairs with sem_down(). */
void restart_kthread(struct kthread *kthread)
{
        struct per_cpu_info *pcpui = &per_cpu_info[core_id()];
        uintptr_t current_stacktop;
        struct kthread *current_kthread;
        /* Avoid messy complications.  The kthread will enable_irqsave() when it
         * comes back up. */
        disable_irq();
        /* Free any spare, since we need the current to become the spare.  Without
         * the spare, we can't free our current kthread/stack (we could free the
         * kthread, but not the stack, since we're still on it).  And we can't free
         * anything after popping kthread, since we never return. */
        if (pcpui->spare) {
                put_kstack(pcpui->spare->stacktop);
                kmem_cache_free(kthread_kcache, pcpui->spare);
        }
        current_kthread = pcpui->cur_kthread;
        current_stacktop = current_kthread->stacktop;
        /* Set the spare stuff (current kthread, which includes its stacktop) */
        pcpui->spare = current_kthread;
        /* When a kthread runs, its stack is the default kernel stack */
        set_stack_top(kthread->stacktop);
        pcpui->cur_kthread = kthread;
#ifdef CONFIG_KTHREAD_POISON
        /* Assert and switch to cur stack not in use, kthr stack in use */
        uintptr_t *cur_stack_poison, *kth_stack_poison;
        cur_stack_poison = kstack_bottom_addr(current_stacktop);
        assert(*cur_stack_poison == 0xdeadbeef);
        *cur_stack_poison = 0;
        kth_stack_poison = kstack_bottom_addr(kthread->stacktop);
        assert(!*kth_stack_poison);
        *kth_stack_poison = 0xdeadbeef;
#endif /* CONFIG_KTHREAD_POISON */
        /* Only change current if we need to (the kthread was in process context) */
        if (kthread->proc) {
                /* Load our page tables before potentially decreffing cur_proc */
                lcr3(kthread->proc->env_cr3);
                /* Might have to clear out an existing current.  If they need to be set
                 * later (like in restartcore), it'll be done on demand. */
                if (pcpui->cur_proc)
                        proc_decref(pcpui->cur_proc);
                /* We also transfer our counted ref from kthread->proc to cur_proc */
                pcpui->cur_proc = kthread->proc;
        }
        /* Tell the core which syscall we are running (if any) */
        assert(!pcpui->cur_sysc);       /* catch bugs, prev user should clear */
        pcpui->cur_sysc = kthread->sysc;
        pcpui->cur_errbuf = kthread->errbuf;
        /* Finally, restart our thread */
        pop_kernel_ctx(&kthread->context);
}

/* Kmsg handler to launch/run a kthread.  This must be a routine message, since
 * it does not return.  */
static void __launch_kthread(uint32_t srcid, long a0, long a1, long a2)
{
        struct kthread *kthread = (struct kthread*)a0;
        struct per_cpu_info *pcpui = &per_cpu_info[core_id()];
        struct proc *cur_proc = pcpui->cur_proc;
        
        /* Make sure we are a routine kmsg */
        assert(in_early_rkmsg_ctx(pcpui));
        if (pcpui->owning_proc && pcpui->owning_proc != kthread->proc) {
                /* Some process should be running here that is not the same as the
                 * kthread.  This means the _M is getting interrupted or otherwise
                 * delayed.  If we want to do something other than run it (like send the
                 * kmsg to another pcore, or ship the context from here to somewhere
                 * else/deschedule it (like for an _S)), do it here.
                 *
                 * If you want to do something here, call out to the ksched, then
                 * abandon_core(). */
                cmb();  /* do nothing/placeholder */
        }
        /* o/w, just run the kthread.  any trapframes that are supposed to run or
         * were interrupted will run whenever the kthread smp_idles() or otherwise
         * finishes.  We also need to clear the RKMSG context since we will not
         * return from restart_kth. */
        clear_rkmsg(pcpui);
        restart_kthread(kthread);
        assert(0);
}

/* Call this when a kthread becomes runnable/unblocked.  We don't do anything
 * particularly smart yet, but when we do, we can put it here. */
void kthread_runnable(struct kthread *kthread)
{
        uint32_t dst = core_id();
        #if 0
        /* turn this block on if you want to test migrating non-core0 kthreads */
        switch (dst) {
                case 0:
                        break;
                case 7:
                        dst = 2;
                        break;
                default:
                        dst++;
        }
        #endif
        /* For lack of anything better, send it to ourselves. (TODO: KSCHED) */
        send_kernel_message(dst, __launch_kthread, (long)kthread, 0, 0,
                            KMSG_ROUTINE);
}

/* Kmsg helper for kthread_yield */
static void __wake_me_up(uint32_t srcid, long a0, long a1, long a2)
{
        struct semaphore *sem = (struct semaphore*)a0;
        assert(sem_up(sem));
}

/* Stop the current kthread.  It'll get woken up next time we run routine kmsgs,
 * after all existing kmsgs are processed. */
void kthread_yield(void)
{
        struct semaphore local_sem, *sem = &local_sem;
        sem_init(sem, 0);
        send_kernel_message(core_id(), __wake_me_up, (long)sem, 0, 0,
                            KMSG_ROUTINE);
        sem_down(sem);
}

void check_poison(char *msg)
{
#ifdef CONFIG_KTHREAD_POISON
        struct per_cpu_info *pcpui = &per_cpu_info[core_id()];
        assert(pcpui->cur_kthread && pcpui->cur_kthread->stacktop);
        if (*kstack_bottom_addr(pcpui->cur_kthread->stacktop) != 0xdeadbeef) {
                printk("\nBad kthread canary, msg: %s\n", msg);
                panic("");
        }
#endif /* CONFIG_KTHREAD_POISON */
}

/* Semaphores, using kthreads directly */
void sem_init(struct semaphore *sem, int signals)
{
        TAILQ_INIT(&sem->waiters);
        sem->nr_signals = signals;
        spinlock_init(&sem->lock);
        sem->irq_okay = FALSE;
}

void sem_init_irqsave(struct semaphore *sem, int signals)
{
        TAILQ_INIT(&sem->waiters);
        sem->nr_signals = signals;
        spinlock_init_irqsave(&sem->lock);
        sem->irq_okay = TRUE;
}

/* This downs the semaphore and suspends the current kernel context on its
 * waitqueue if there are no pending signals.  Note that the case where the
 * signal is already there is not optimized. */
void sem_down(struct semaphore *sem)
{
        volatile bool blocking = TRUE;  /* signal to short circuit when restarting*/
        struct kthread *kthread, *new_kthread;
        register uintptr_t new_stacktop;
        struct per_cpu_info *pcpui = &per_cpu_info[core_id()];

        assert(can_block(pcpui));
        /* Make sure we aren't holding any locks (only works if SPINLOCK_DEBUG) */
        assert(!pcpui->lock_depth);
        assert(pcpui->cur_kthread);
        /* Try to down the semaphore.  If there is a signal there, we can skip all
         * of the sleep prep and just return. */
        spin_lock(&sem->lock);  /* no need for irqsave, since we disabled ints */
        if (sem->nr_signals > 0) {
                sem->nr_signals--;
                spin_unlock(&sem->lock);
                goto block_return_path;
        }
        spin_unlock(&sem->lock);
        /* We're probably going to sleep, so get ready.  We'll check again later. */
        kthread = pcpui->cur_kthread;
        /* We need to have a spare slot for restart, so we also use it when
         * sleeping.  Right now, we need a new kthread to take over if/when our
         * current kthread sleeps.  Use the spare, and if not, get a new one.
         *
         * Note we do this with interrupts disabled (which protects us from
         * concurrent modifications). */
        if (pcpui->spare) {
                new_kthread = pcpui->spare;
                new_stacktop = new_kthread->stacktop;
                pcpui->spare = 0;
        } else {
                new_kthread = __kthread_zalloc();
                new_stacktop = get_kstack();
                new_kthread->stacktop = new_stacktop;
#ifdef CONFIG_KTHREAD_POISON
                *kstack_bottom_addr(new_stacktop) = 0;
#endif /* CONFIG_KTHREAD_POISON */
        }
        /* Set the core's new default stack and kthread */
        set_stack_top(new_stacktop);
        pcpui->cur_kthread = new_kthread;
#ifdef CONFIG_KTHREAD_POISON
        /* Mark the new stack as in-use, and unmark the current kthread */
        uintptr_t *new_stack_poison, *kth_stack_poison;
        new_stack_poison = kstack_bottom_addr(new_stacktop);
        assert(!*new_stack_poison);
        *new_stack_poison = 0xdeadbeef;
        kth_stack_poison = kstack_bottom_addr(kthread->stacktop);
        assert(*kth_stack_poison == 0xdeadbeef);
        *kth_stack_poison = 0;
#endif /* CONFIG_KTHREAD_POISON */
        /* The kthread needs to stay in the process context (if there is one), but
         * we want the core (which could be a vcore) to stay in the context too.  In
         * the future, we could check owning_proc. If it isn't set, we could leave
         * the process context and transfer the refcnt to kthread->proc. */
        kthread->proc = current;
        /* kthread tracks the syscall it is working on, which implies errno */
        kthread->sysc = pcpui->cur_sysc;
        kthread->errbuf = pcpui->cur_errbuf;
        pcpui->cur_sysc = 0;                            /* this core no longer works on sysc */
        pcpui->cur_errbuf = 0;                          /* this core no longer has an errbuf */
        if (kthread->proc)
                proc_incref(kthread->proc, 1);
        /* Save the context, toggle blocking for the reactivation */
        save_kernel_ctx(&kthread->context);
        if (!blocking)
                goto block_return_path;
        blocking = FALSE;                                       /* for when it starts back up */
        /* Down the semaphore.  We need this to be inline.  If we're sleeping, once
         * we unlock the kthread could be started up again and can return and start
         * trashing this function's stack, hence the weird control flow. */
        spin_lock(&sem->lock);
        if (sem->nr_signals-- <= 0) {
                TAILQ_INSERT_TAIL(&sem->waiters, kthread, link);
                /* At this point, we know we'll sleep and change stacks later.  Once we
                 * unlock, we could have the kthread restarted (possibly on another
                 * core), so we need to disable irqs until we are on our new stack.
                 * Otherwise, if we take an IRQ, we'll be using our stack while another
                 * core is using it (restarted kthread).  Basically, disabling irqs
                 * allows us to atomically unlock and 'yield'. */
                disable_irq();
        } else {                                                        /* we didn't sleep */
                goto unwind_sleep_prep;
        }
        spin_unlock(&sem->lock);
        /* Switch to the core's default stack.  After this, don't use local
         * variables.  TODO: we shouldn't be using new_stacktop either, can't always
         * trust the register keyword (AFAIK). */
        set_stack_pointer(new_stacktop);
        smp_idle();                                                     /* reenables irqs eventually */
        /* smp_idle never returns */
        assert(0);
unwind_sleep_prep:
        /* We get here if we should not sleep on sem (the signal beat the sleep).
         * Note we are not optimizing for cases where the signal won. */
        spin_unlock(&sem->lock);
        printd("[kernel] Didn't sleep, unwinding...\n");
        /* Restore the core's current and default stacktop */
        current = kthread->proc;                        /* arguably unnecessary */
        if (kthread->proc)
                proc_decref(kthread->proc);
        set_stack_top(kthread->stacktop);
        pcpui->cur_kthread = kthread;
        /* Save the allocs as the spare */
        assert(!pcpui->spare);
        pcpui->spare = new_kthread;
#ifdef CONFIG_KTHREAD_POISON
        /* switch back to old stack in use, new one not */
        *new_stack_poison = 0;
        *kth_stack_poison = 0xdeadbeef;
#endif /* CONFIG_KTHREAD_POISON */
block_return_path:
        printd("[kernel] Returning from being 'blocked'! at %llu\n", read_tsc());
        return;
}

/* Ups the semaphore.  If it was < 0, we need to wake up someone, which we do.
 * Returns TRUE if we woke someone, FALSE o/w (used for debugging in some
 * places).  If we need more control, we can implement a version of the old
 * __up_sem() again.  */
bool sem_up(struct semaphore *sem)
{
        struct kthread *kthread = 0;
        spin_lock(&sem->lock);
        if (sem->nr_signals++ < 0) {
                assert(!TAILQ_EMPTY(&sem->waiters));
                /* could do something with 'priority' here */
                kthread = TAILQ_FIRST(&sem->waiters);
                TAILQ_REMOVE(&sem->waiters, kthread, link);
        } else {
                assert(TAILQ_EMPTY(&sem->waiters));
        }
        spin_unlock(&sem->lock);
        /* Note that once we call kthread_runnable(), we cannot touch the sem again.
         * Some sems are on stacks.  The caller can touch sem, if it knows about the
         * memory/usage of the sem.  Likewise, we can't touch the kthread either. */
        if (kthread) {
                kthread_runnable(kthread);
                return TRUE;
        }
        return FALSE;
}

void sem_down_irqsave(struct semaphore *sem, int8_t *irq_state)
{
        disable_irqsave(irq_state);
        sem_down(sem);
        enable_irqsave(irq_state);
}

bool sem_up_irqsave(struct semaphore *sem, int8_t *irq_state)
{
        bool retval;
        disable_irqsave(irq_state);
        retval = sem_up(sem);
        enable_irqsave(irq_state);
        return retval;
}

/* Condition variables, using semaphores and kthreads */
void cv_init(struct cond_var *cv)
{
        sem_init(&cv->sem, 0);
        cv->lock = &cv->internal_lock;
        spinlock_init(cv->lock);
        cv->nr_waiters = 0;
        cv->irq_okay = FALSE;
}

void cv_init_irqsave(struct cond_var *cv)
{
        sem_init_irqsave(&cv->sem, 0);
        cv->lock = &cv->internal_lock;
        spinlock_init_irqsave(cv->lock);
        cv->nr_waiters = 0;
        cv->irq_okay = TRUE;
}

void cv_init_with_lock(struct cond_var *cv, spinlock_t *lock)
{
        sem_init(&cv->sem, 0);
        cv->nr_waiters = 0;
        cv->lock = lock;
        cv->irq_okay = FALSE;
}

void cv_init_irqsave_with_lock(struct cond_var *cv, spinlock_t *lock)
{
        sem_init_irqsave(&cv->sem, 0);
        cv->nr_waiters = 0;
        cv->lock = lock;
        cv->irq_okay = TRUE;
}

void cv_lock(struct cond_var *cv)
{
        spin_lock(cv->lock);
}

void cv_unlock(struct cond_var *cv)
{
        spin_unlock(cv->lock);
}

void cv_lock_irqsave(struct cond_var *cv, int8_t *irq_state)
{
        disable_irqsave(irq_state);
        cv_lock(cv);
}

void cv_unlock_irqsave(struct cond_var *cv, int8_t *irq_state)
{
        cv_unlock(cv);
        enable_irqsave(irq_state);
}

/* Helper to clarify the wait/signalling code */
static int nr_sem_waiters(struct semaphore *sem)
{
        int retval;
        retval = 0 - sem->nr_signals;
        assert(retval >= 0);
        return retval;
}

/* Comes in locked.  Note we don't mess with enabling/disabling irqs.  The
 * initial cv_lock would have disabled irqs (if applicable), and we don't mess
 * with that setting at all. */
void cv_wait_and_unlock(struct cond_var *cv)
{
        unsigned long nr_prev_waiters;
        nr_prev_waiters = cv->nr_waiters++;
        spin_unlock(cv->lock);
        /* Wait til our turn.  This forces an ordering of all waiters such that the
         * order in which they wait is the order in which they down the sem. */
        while (nr_prev_waiters != nr_sem_waiters(&cv->sem))
                cpu_relax();
        printd("core %d, sees nr_sem_waiters: %d, cv_nr_waiters %d\n",
               core_id(), nr_sem_waiters(&cv->sem), cv->nr_waiters);
        /* Atomically sleeps and 'unlocks' the next kthread from its busy loop (the
         * one right above this), when it changes the sems nr_signals/waiters. */
        sem_down(&cv->sem);
}

/* Comes in locked.  Note cv_lock does not disable irqs.   They should still be
 * disabled from the initial cv_lock_irqsave(). */
void cv_wait(struct cond_var *cv)
{
        cv_wait_and_unlock(cv);
        if (cv->irq_okay)
                assert(!irq_is_enabled());
        cv_lock(cv);
}

/* Helper, wakes exactly one, and there should have been at least one waiter. */
static void sem_wake_one(struct semaphore *sem)
{
        struct kthread *kthread;
        /* these locks will be irqsaved if the CV is irqsave (only need the one) */
        spin_lock(&sem->lock);
        assert(sem->nr_signals < 0);
        sem->nr_signals++;
        kthread = TAILQ_FIRST(&sem->waiters);
        TAILQ_REMOVE(&sem->waiters, kthread, link);
        spin_unlock(&sem->lock);
        kthread_runnable(kthread);
}

void __cv_signal(struct cond_var *cv)
{
        /* Can't short circuit this stuff.  We need to make sure any waiters that
         * made it past upping the cv->nr_waiters has also downed the sem.
         * Otherwise we muck with nr_waiters, which could break the ordering
         * required by the waiters.  We also need to lock while making this check,
         * o/w a new waiter can slip in after our while loop. */
        while (cv->nr_waiters != nr_sem_waiters(&cv->sem))
                cpu_relax();
        if (cv->nr_waiters) {
                cv->nr_waiters--;
                sem_wake_one(&cv->sem);
        }
}

void __cv_broadcast(struct cond_var *cv)
{
        while (cv->nr_waiters != nr_sem_waiters(&cv->sem))
                cpu_relax();
        while (cv->nr_waiters) {
                cv->nr_waiters--;
                sem_wake_one(&cv->sem);
        }
}

void cv_signal(struct cond_var *cv)
{
        spin_lock(cv->lock);
        __cv_signal(cv);
        spin_unlock(cv->lock);
}

void cv_broadcast(struct cond_var *cv)
{
        spin_lock(cv->lock);
        __cv_broadcast(cv);
        spin_unlock(cv->lock);
}

void cv_signal_irqsave(struct cond_var *cv, int8_t *irq_state)
{
        disable_irqsave(irq_state);
        cv_signal(cv);
        enable_irqsave(irq_state);
}

void cv_broadcast_irqsave(struct cond_var *cv, int8_t *irq_state)
{
        disable_irqsave(irq_state);
        cv_broadcast(cv);
        enable_irqsave(irq_state);
}