/*
 * JFFS2 -- Journalling Flash File System, Version 2.
 *
 * Copyright © 2001-2007 Red Hat, Inc.
 * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
 *
 * Created by David Woodhouse <dwmw2@infradead.org>
 *
 * For licensing information, see the file 'LICENCE' in this directory.
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/jffs2.h>
#include <linux/mtd/mtd.h>
#include <linux/completion.h>
#include <linux/sched/signal.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
#include "nodelist.h"


static int jffs2_garbage_collect_thread(void *);

void jffs2_garbage_collect_trigger(struct jffs2_sb_info *c)
{
        assert_spin_locked(&c->erase_completion_lock);
        if (c->gc_task && jffs2_thread_should_wake(c))
                send_sig(SIGHUP, c->gc_task, 1);
}

/* This must only ever be called when no GC thread is currently running */
int jffs2_start_garbage_collect_thread(struct jffs2_sb_info *c)
{
        struct task_struct *tsk;
        int ret = 0;

        BUG_ON(c->gc_task);

        init_completion(&c->gc_thread_start);
        init_completion(&c->gc_thread_exit);

        tsk = kthread_run(jffs2_garbage_collect_thread, c, "jffs2_gcd_mtd%d", c->mtd->index);
        if (IS_ERR(tsk)) {
                pr_warn("fork failed for JFFS2 garbage collect thread: %pe\n",
                        tsk);
                complete(&c->gc_thread_exit);
                ret = PTR_ERR(tsk);
        } else {
                /* Wait for it... */
                jffs2_dbg(1, "Garbage collect thread is pid %d\n", tsk->pid);
                wait_for_completion(&c->gc_thread_start);
                ret = tsk->pid;
        }

        return ret;
}

void jffs2_stop_garbage_collect_thread(struct jffs2_sb_info *c)
{
        int wait = 0;
        spin_lock(&c->erase_completion_lock);
        if (c->gc_task) {
                jffs2_dbg(1, "Killing GC task %d\n", c->gc_task->pid);
                send_sig(SIGKILL, c->gc_task, 1);
                wait = 1;
        }
        spin_unlock(&c->erase_completion_lock);
        if (wait)
                wait_for_completion(&c->gc_thread_exit);
}

static int jffs2_garbage_collect_thread(void *_c)
{
        struct jffs2_sb_info *c = _c;
        sigset_t hupmask;

        siginitset(&hupmask, sigmask(SIGHUP));
        allow_signal(SIGKILL);
        allow_signal(SIGSTOP);
        allow_signal(SIGHUP);

        c->gc_task = current;
        complete(&c->gc_thread_start);

        set_user_nice(current, 10);

        set_freezable();
        for (;;) {
                sigprocmask(SIG_UNBLOCK, &hupmask, NULL);
        again:
                spin_lock(&c->erase_completion_lock);
                if (!jffs2_thread_should_wake(c)) {
                        set_current_state (TASK_INTERRUPTIBLE);
                        spin_unlock(&c->erase_completion_lock);
                        jffs2_dbg(1, "%s(): sleeping...\n", __func__);
                        schedule();
                } else {
                        spin_unlock(&c->erase_completion_lock);
                }
                /* Problem - immediately after bootup, the GCD spends a lot
                 * of time in places like jffs2_kill_fragtree(); so much so
                 * that userspace processes (like gdm and X) are starved
                 * despite plenty of cond_resched()s and renicing.  Yield()
                 * doesn't help, either (presumably because userspace and GCD
                 * are generally competing for a higher latency resource -
                 * disk).
                 * This forces the GCD to slow the hell down.   Pulling an
                 * inode in with read_inode() is much preferable to having
                 * the GC thread get there first. */
                schedule_timeout_interruptible(msecs_to_jiffies(50));

                if (kthread_should_stop()) {
                        jffs2_dbg(1, "%s(): kthread_stop() called\n", __func__);
                        goto die;
                }

                /* Put_super will send a SIGKILL and then wait on the sem.
                 */
                while (signal_pending(current) || freezing(current)) {
                        unsigned long signr;

                        if (try_to_freeze())
                                goto again;

                        signr = kernel_dequeue_signal();

                        switch(signr) {
                        case SIGSTOP:
                                jffs2_dbg(1, "%s(): SIGSTOP received\n",
                                          __func__);
                                kernel_signal_stop();
                                break;

                        case SIGKILL:
                                jffs2_dbg(1, "%s(): SIGKILL received\n",
                                          __func__);
                                goto die;

                        case SIGHUP:
                                jffs2_dbg(1, "%s(): SIGHUP received\n",
                                          __func__);
                                break;
                        default:
                                jffs2_dbg(1, "%s(): signal %ld received\n",
                                          __func__, signr);
                        }
                }
                /* We don't want SIGHUP to interrupt us. STOP and KILL are OK though. */
                sigprocmask(SIG_BLOCK, &hupmask, NULL);

                jffs2_dbg(1, "%s(): pass\n", __func__);
                if (jffs2_garbage_collect_pass(c) == -ENOSPC) {
                        pr_notice("No space for garbage collection. Aborting GC thread\n");
                        goto die;
                }
        }
 die:
        spin_lock(&c->erase_completion_lock);
        c->gc_task = NULL;
        spin_unlock(&c->erase_completion_lock);
        kthread_complete_and_exit(&c->gc_thread_exit, 0);
}