exit.c

unix/linux 编程实践一书的所有源代码

/*
 *  linux/kernel/exit.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/config.h>
#include <linux/malloc.h>
#include <linux/interrupt.h>
#include <linux/smp_lock.h>
#include <linux/module.h>
#include <linux/vmalloc.h>
#ifdef CONFIG_BSD_PROCESS_ACCT
#include <linux/acct.h>
#endif

#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/mmu_context.h>

extern void sem_exit (void);
extern struct task_struct *child_reaper;

int getrusage(struct task_struct *, int, struct rusage *);

void release(struct task_struct * p)
{
	if (p != current) {
#ifdef __SMP__
		/*
		 * Wait to make sure the process isn't active on any
		 * other CPU
		 */
		for (;;)  {
			int has_cpu;
			spin_lock_irq(&runqueue_lock);
			has_cpu = p->has_cpu;
			spin_unlock_irq(&runqueue_lock);
			if (!has_cpu)
				break;
			do {
				barrier();
			} while (p->has_cpu);
		}
#endif
		free_uid(p);
		add_free_taskslot(p->tarray_ptr);

		write_lock_irq(&tasklist_lock);
		nr_tasks--;
		unhash_pid(p);
		REMOVE_LINKS(p);
		write_unlock_irq(&tasklist_lock);

		release_thread(p);
		current->cmin_flt += p->min_flt + p->cmin_flt;
		current->cmaj_flt += p->maj_flt + p->cmaj_flt;
		current->cnswap += p->nswap + p->cnswap;
		free_task_struct(p);
	} else {
		printk("task releasing itself\n");
	}
}

/*
 * This checks not only the pgrp, but falls back on the pid if no
 * satisfactory pgrp is found. I dunno - gdb doesn't work correctly
 * without this...
 */
int session_of_pgrp(int pgrp)
{
	struct task_struct *p;
	int fallback;

	fallback = -1;
	read_lock(&tasklist_lock);
	for_each_task(p) {
 		if (p->session <= 0)
 			continue;
		if (p->pgrp == pgrp) {
			fallback = p->session;
			break;
		}
		if (p->pid == pgrp)
			fallback = p->session;
	}
	read_unlock(&tasklist_lock);
	return fallback;
}

/*
 * Determine if a process group is "orphaned", according to the POSIX
 * definition in 2.2.2.52.  Orphaned process groups are not to be affected
 * by terminal-generated stop signals.  Newly orphaned process groups are
 * to receive a SIGHUP and a SIGCONT.
 *
 * "I ask you, have you ever known what it is to be an orphan?"
 */
static int will_become_orphaned_pgrp(int pgrp, struct task_struct * ignored_task)
{
	struct task_struct *p;

	read_lock(&tasklist_lock);
	for_each_task(p) {
		if ((p == ignored_task) || (p->pgrp != pgrp) ||
		    (p->state == TASK_ZOMBIE) ||
		    (p->p_pptr->pid == 1))
			continue;
		if ((p->p_pptr->pgrp != pgrp) &&
		    (p->p_pptr->session == p->session)) {
			read_unlock(&tasklist_lock);
 			return 0;
		}
	}
	read_unlock(&tasklist_lock);
	return 1;	/* (sighing) "Often!" */
}

int is_orphaned_pgrp(int pgrp)
{
	return will_become_orphaned_pgrp(pgrp, 0);
}

static inline int has_stopped_jobs(int pgrp)
{
	int retval = 0;
	struct task_struct * p;

	read_lock(&tasklist_lock);
	for_each_task(p) {
		if (p->pgrp != pgrp)
			continue;
		if (p->state != TASK_STOPPED)
			continue;
		retval = 1;
		break;
	}
	read_unlock(&tasklist_lock);
	return retval;
}

static inline void forget_original_parent(struct task_struct * father)
{
	struct task_struct * p;

	read_lock(&tasklist_lock);
	for_each_task(p) {
		if (p->p_opptr == father) {
			/* We dont want people slaying init */
			p->exit_signal = SIGCHLD;
			p->self_exec_id++;
			p->p_opptr = child_reaper; /* init */
			if (p->pdeath_signal) send_sig(p->pdeath_signal, p, 0);
		}
	}
	read_unlock(&tasklist_lock);
}

static inline void close_files(struct files_struct * files)
{
	int i, j;

	j = 0;
	for (;;) {
		unsigned long set;
		i = j * __NFDBITS;
		if (i >= files->max_fdset || i >= files->max_fds)
			break;
		set = files->open_fds->fds_bits[j++];
		while (set) {
			if (set & 1) {
				struct file * file = files->fd[i];
				if (file) {
					files->fd[i] = NULL;
					filp_close(file, files);
				}
			}
			i++;
			set >>= 1;
		}
	}
}

extern kmem_cache_t *files_cachep;  

static inline void __exit_files(struct task_struct *tsk)
{
	struct files_struct * files = tsk->files;

	if (files) {
		tsk->files = NULL;
		if (atomic_dec_and_test(&files->count)) {
			close_files(files);
			/*
 			 * Free the fd and fdset arrays if we expanded them.
			 */
 			if (files->fd != &files->fd_array[0])
 				free_fd_array(files->fd, files->max_fds);
 			if (files->max_fdset > __FD_SETSIZE) {
 				free_fdset(files->open_fds, files->max_fdset);
 				free_fdset(files->close_on_exec, files->max_fdset);
 			}
			kmem_cache_free(files_cachep, files);
		}
	}
}

void exit_files(struct task_struct *tsk)
{
	__exit_files(tsk);
}

static inline void __exit_fs(struct task_struct *tsk)
{
	struct fs_struct * fs = tsk->fs;

	if (fs) {
		tsk->fs = NULL;
		if (atomic_dec_and_test(&fs->count)) {
			dput(fs->root);
			dput(fs->pwd);
			kfree(fs);
		}
	}
}

void exit_fs(struct task_struct *tsk)
{
	__exit_fs(tsk);
}

static inline void __exit_sighand(struct task_struct *tsk)
{
	struct signal_struct * sig = tsk->sig;
	unsigned long flags;

	spin_lock_irqsave(&tsk->sigmask_lock, flags);
	if (sig) {
		tsk->sig = NULL;
		if (atomic_dec_and_test(&sig->count))
			kfree(sig);
	}

	flush_signals(tsk);
	spin_unlock_irqrestore(&tsk->sigmask_lock, flags);
}

void exit_sighand(struct task_struct *tsk)
{
	__exit_sighand(tsk);
}

static inline void __exit_mm(struct task_struct * tsk)
{
	struct mm_struct * mm = tsk->mm;

	/* Set us up to use the kernel mm state */
	if (mm != &init_mm) {
		flush_cache_mm(mm);
		flush_tlb_mm(mm);
		destroy_context(mm);
		tsk->mm = &init_mm;
		tsk->swappable = 0;
		SET_PAGE_DIR(tsk, swapper_pg_dir);
		mm_release();
		mmput(mm);
	}
}

void exit_mm(struct task_struct *tsk)
{
	__exit_mm(tsk);
}

/*
 * Send signals to all our closest relatives so that they know
 * to properly mourn us..
 */
static void exit_notify(void)
{
	struct task_struct * p, *t;

	forget_original_parent(current);
	/*
	 * Check to see if any process groups have become orphaned
	 * as a result of our exiting, and if they have any stopped
	 * jobs, send them a SIGHUP and then a SIGCONT.  (POSIX 3.2.2.2)
	 *
	 * Case i: Our father is in a different pgrp than we are
	 * and we were the only connection outside, so our pgrp
	 * is about to become orphaned.
	 */
	 
	t = current->p_pptr;
	
	if ((t->pgrp != current->pgrp) &&
	    (t->session == current->session) &&
	    will_become_orphaned_pgrp(current->pgrp, current) &&
	    has_stopped_jobs(current->pgrp)) {
		kill_pg(current->pgrp,SIGHUP,1);
		kill_pg(current->pgrp,SIGCONT,1);
	}

	/* Let father know we died 
	 *
	 * Thread signals are configurable, but you aren't going to use
	 * that to send signals to arbitary processes. 
	 * That stops right now.
	 *
	 * If the parent exec id doesn't match the exec id we saved
	 * when we started then we know the parent has changed security
	 * domain.
	 *
	 * If our self_exec id doesn't match our parent_exec_id then
	 * we have changed execution domain as these two values started
	 * the same after a fork.
	 *	
	 */
	
	if(current->exit_signal != SIGCHLD &&
	    ( current->parent_exec_id != t->self_exec_id  ||
	      current->self_exec_id != current->parent_exec_id) 
	    && !capable(CAP_KILL))
		current->exit_signal = SIGCHLD;

	notify_parent(current, current->exit_signal);

	/*
	 * This loop does two things:
	 *
  	 * A.  Make init inherit all the child processes
	 * B.  Check to see if any process groups have become orphaned
	 *	as a result of our exiting, and if they have any stopped
	 *	jobs, send them a SIGHUP and then a SIGCONT.  (POSIX 3.2.2.2)
	 */

	write_lock_irq(&tasklist_lock);
	while (current->p_cptr != NULL) {
		p = current->p_cptr;
		current->p_cptr = p->p_osptr;
		p->p_ysptr = NULL;
		p->flags &= ~(PF_PTRACED|PF_TRACESYS);

		p->p_pptr = p->p_opptr;
		p->p_osptr = p->p_pptr->p_cptr;
		if (p->p_osptr)
			p->p_osptr->p_ysptr = p;
		p->p_pptr->p_cptr = p;
		if (p->state == TASK_ZOMBIE)
			notify_parent(p, p->exit_signal);
		/*
		 * process group orphan check
		 * Case ii: Our child is in a different pgrp
		 * than we are, and it was the only connection
		 * outside, so the child pgrp is now orphaned.
		 */
		if ((p->pgrp != current->pgrp) &&
		    (p->session == current->session)) {
			int pgrp = p->pgrp;

			write_unlock_irq(&tasklist_lock);
			if (is_orphaned_pgrp(pgrp) && has_stopped_jobs(pgrp)) {
				kill_pg(pgrp,SIGHUP,1);
				kill_pg(pgrp,SIGCONT,1);
			}
			write_lock_irq(&tasklist_lock);
		}
	}
	write_unlock_irq(&tasklist_lock);

	if (current->leader)
		disassociate_ctty(1);
}

NORET_TYPE void do_exit(long code)
{
	struct task_struct *tsk = current;

	if (in_interrupt())
		printk("Aiee, killing interrupt handler\n");
	if (!tsk->pid)
		panic("Attempted to kill the idle task!");
	tsk->flags |= PF_EXITING;
	start_bh_atomic();
	del_timer(&tsk->real_timer);
	end_bh_atomic();

	lock_kernel();
fake_volatile:
#ifdef CONFIG_BSD_PROCESS_ACCT
	acct_process(code);
#endif
	sem_exit();
	__exit_mm(tsk);
#if CONFIG_AP1000
	exit_msc(tsk);
#endif
	__exit_files(tsk);
	__exit_fs(tsk);
	__exit_sighand(tsk);
	exit_thread();
	tsk->state = TASK_ZOMBIE;
	tsk->exit_code = code;
	exit_notify();
#ifdef DEBUG_PROC_TREE
	audit_ptree();
#endif
	if (tsk->exec_domain && tsk->exec_domain->module)
		__MOD_DEC_USE_COUNT(tsk->exec_domain->module);
	if (tsk->binfmt && tsk->binfmt->module)
		__MOD_DEC_USE_COUNT(tsk->binfmt->module);
	schedule();
/*
 * In order to get rid of the "volatile function does return" message
 * I did this little loop that confuses gcc to think do_exit really
 * is volatile. In fact it's schedule() that is volatile in some
 * circumstances: when current->state = ZOMBIE, schedule() never
 * returns.
 *
 * In fact the natural way to do all this is to have the label and the
 * goto right after each other, but I put the fake_volatile label at
 * the start of the function just in case something /really/ bad
 * happens, and the schedule returns. This way we can try again. I'm
 * not paranoid: it's just that everybody is out to get me.
 */
	goto fake_volatile;
}

asmlinkage int sys_exit(int error_code)
{
	do_exit((error_code&0xff)<<8);
}

asmlinkage int sys_wait4(pid_t pid,unsigned int * stat_addr, int options, struct rusage * ru)
{
	int flag, retval;
	struct wait_queue wait = { current, NULL };
	struct task_struct *p;

	if (options & ~(WNOHANG|WUNTRACED|__WCLONE))
		return -EINVAL;

	add_wait_queue(&current->wait_chldexit,&wait);
repeat:
	flag = 0;

	/* The interruptible state must be set before looking at the
	   children. This because we want to catch any racy exit from
	   the children as do_exit() may run under us. The following
	   read_lock will enforce SMP ordering at the CPU level. */
	current->state = TASK_INTERRUPTIBLE;

	read_lock(&tasklist_lock);
 	for (p = current->p_cptr ; p ; p = p->p_osptr) {
		if (pid>0) {
			if (p->pid != pid)
				continue;
		} else if (!pid) {
			if (p->pgrp != current->pgrp)
				continue;
		} else if (pid != -1) {
			if (p->pgrp != -pid)
				continue;
		}
		/* wait for cloned processes iff the __WCLONE flag is set */
		if ((p->exit_signal != SIGCHLD) ^ ((options & __WCLONE) != 0))
			continue;
		flag = 1;
		switch (p->state) {
			case TASK_STOPPED:
				if (!p->exit_code)
					continue;
				if (!(options & WUNTRACED) && !(p->flags & PF_PTRACED))
					continue;
				read_unlock(&tasklist_lock);
				current->state = TASK_RUNNING;	/* We *must* do this before touching userspace! */
				retval = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0; 
				if (!retval && stat_addr) 
					retval = put_user((p->exit_code << 8) | 0x7f, stat_addr);
				if (!retval) {
					p->exit_code = 0;
					retval = p->pid;
				}
				goto end_wait4;
			case TASK_ZOMBIE:
				current->times.tms_cutime += p->times.tms_utime + p->times.tms_cutime;
				current->times.tms_cstime += p->times.tms_stime + p->times.tms_cstime;
				read_unlock(&tasklist_lock);
				current->state = TASK_RUNNING;	/* We *must* do this before touching userspace! */
				retval = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0;
				if (!retval && stat_addr)
					retval = put_user(p->exit_code, stat_addr);
				if (retval)
					goto end_wait4; 
				retval = p->pid;
				if (p->p_opptr != p->p_pptr) {
					write_lock_irq(&tasklist_lock);
					REMOVE_LINKS(p);
					p->p_pptr = p->p_opptr;
					SET_LINKS(p);
					write_unlock_irq(&tasklist_lock);
					notify_parent(p, SIGCHLD);
				} else
					release(p);
#ifdef DEBUG_PROC_TREE
				audit_ptree();
#endif
				goto end_wait4;
			default:
				continue;
		}
	}
	read_unlock(&tasklist_lock);
	if (flag) {
		retval = 0;
		if (options & WNOHANG)
			goto end_wait4;
		retval = -ERESTARTSYS;
		if (signal_pending(current))
			goto end_wait4;
		schedule();
		goto repeat;
	}
	retval = -ECHILD;
end_wait4:
	remove_wait_queue(&current->wait_chldexit,&wait);
	current->state = TASK_RUNNING;
	return retval;
}

#ifndef __alpha__

/*
 * sys_waitpid() remains for compatibility. waitpid() should be
 * implemented by calling sys_wait4() from libc.a.
 */
asmlinkage int sys_waitpid(pid_t pid,unsigned int * stat_addr, int options)
{
	return sys_wait4(pid, stat_addr, options, NULL);
}

#endif