background.c

Go to the documentation of this file.

/*
 * JFFS2 -- Journalling Flash File System, Version 2.
 *
 * Copyright © 2001-2007 Red Hat, Inc.
 * Copyright © 2004-2010 David Woodhouse <[email protected]>
 *
 * Created by David Woodhouse <[email protected]>
 *
 * 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.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: %ld\n",
            -PTR_ERR(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;

    allow_signal(SIGKILL);
    allow_signal(SIGSTOP);
    allow_signal(SIGCONT);

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

    set_user_nice(current, 10);

    set_freezable();
    for (;;) {
        allow_signal(SIGHUP);
    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)) {
            siginfo_t info;
            unsigned long signr;

            if (try_to_freeze())
                goto again;

            signr = dequeue_signal_lock(current, &current->blocked, &info);

            switch(signr) {
            case SIGSTOP:
                jffs2_dbg(1, "%s(): SIGSTOP received\n",
                      __func__);
                set_current_state(TASK_STOPPED);
                schedule();
                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. */
        disallow_signal(SIGHUP);

        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);
    complete_and_exit(&c->gc_thread_exit, 0);
}