[PATCH] wait4() WIFSTOPPED starvation fix #1/2

This patch (#1) just converts the task_struct to use struct list_head rather
than direct pointers for maintaining the children list.

arch/i386/kernel/signal.c

@@ -630,8 +630,8 @@ int do_signal(struct pt_regs *regs, sigset_t *oldset)
 				info.si_signo = signr;
 				info.si_errno = 0;
 				info.si_code = SI_USER;
-				info.si_pid = current->p_pptr->pid;
-				info.si_uid = current->p_pptr->uid;
+				info.si_pid = current->parent->pid;
+				info.si_uid = current->parent->uid;
 			}
 
 			/* If the (new) signal is now blocked, requeue it.  */
@@ -670,7 +670,7 @@ int do_signal(struct pt_regs *regs, sigset_t *oldset)
 			case SIGSTOP: {
 				struct signal_struct *sig;
 				current->exit_code = signr;
-				sig = current->p_pptr->sig;
+				sig = current->parent->sig;
 				preempt_disable();
 				current->state = TASK_STOPPED;
 				if (sig && !(sig->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDSTOP))

fs/binfmt_elf.c

@@ -1094,7 +1094,7 @@ static int elf_core_dump(long signr, struct pt_regs * regs, struct file * file)
 	prstatus.pr_sigpend = current->pending.signal.sig[0];
 	prstatus.pr_sighold = current->blocked.sig[0];
 	psinfo.pr_pid = prstatus.pr_pid = current->pid;
-	psinfo.pr_ppid = prstatus.pr_ppid = current->p_pptr->pid;
+	psinfo.pr_ppid = prstatus.pr_ppid = current->parent->pid;
 	psinfo.pr_pgrp = prstatus.pr_pgrp = current->pgrp;
 	psinfo.pr_sid = prstatus.pr_sid = current->session;
 	prstatus.pr_utime.tv_sec = CT_TO_SECS(current->times.tms_utime);

fs/proc/array.c

@@ -159,7 +159,7 @@ static inline char * task_state(struct task_struct *p, char *buffer)
 		"Uid:\t%d\t%d\t%d\t%d\n"
 		"Gid:\t%d\t%d\t%d\t%d\n",
 		get_task_state(p), p->tgid,
-		p->pid, p->pid ? p->p_opptr->pid : 0, 0,
+		p->pid, p->pid ? p->real_parent->pid : 0, 0,
 		p->uid, p->euid, p->suid, p->fsuid,
 		p->gid, p->egid, p->sgid, p->fsgid);
 	read_unlock(&tasklist_lock);	
@@ -340,7 +340,7 @@ int proc_pid_stat(struct task_struct *task, char * buffer)
 	nice = task_nice(task);
 
 	read_lock(&tasklist_lock);
-	ppid = task->pid ? task->p_opptr->pid : 0;
+	ppid = task->pid ? task->real_parent->pid : 0;
 	read_unlock(&tasklist_lock);
 	res = sprintf(buffer,"%d (%s) %c %d %d %d %d %d %lu %lu \
 %lu %lu %lu %lu %lu %ld %ld %ld %ld %ld %ld %lu %lu %ld %lu %lu %lu %lu %lu \

fs/proc/base.c

@@ -336,7 +336,7 @@ static struct file_operations proc_info_file_operations = {
 };
 
 #define MAY_PTRACE(p) \
-(p==current||(p->p_pptr==current&&(p->ptrace & PT_PTRACED)&&p->state==TASK_STOPPED))
+(p==current||(p->parent==current&&(p->ptrace & PT_PTRACED)&&p->state==TASK_STOPPED))
 
 
 static int mem_open(struct inode* inode, struct file* file)

include/linux/init_task.h

@@ -55,8 +55,10 @@
     time_slice:		HZ,						\
     next_task:		&tsk,						\
     prev_task:		&tsk,						\
-    p_opptr:		&tsk,						\
-    p_pptr:		&tsk,						\
+    real_parent:	&tsk,						\
+    parent:		&tsk,						\
+    children:		LIST_HEAD_INIT(tsk.children),			\
+    sibling:		LIST_HEAD_INIT(tsk.sibling),			\
     thread_group:	LIST_HEAD_INIT(tsk.thread_group),		\
     wait_chldexit:	__WAIT_QUEUE_HEAD_INITIALIZER(tsk.wait_chldexit),\
     real_timer:		{						\

include/linux/sched.h

@@ -274,9 +274,12 @@ struct task_struct {
 	/* 
 	 * pointers to (original) parent process, youngest child, younger sibling,
 	 * older sibling, respectively.  (p->father can be replaced with 
-	 * p->p_pptr->pid)
+	 * p->parent->pid)
 	 */
-	struct task_struct *p_opptr, *p_pptr, *p_cptr, *p_ysptr, *p_osptr;
+	struct task_struct *real_parent; /* real parent process (when being debugged) */
+	struct task_struct *parent;	/* parent process */
+	struct list_head children;	/* list of my children */
+	struct list_head sibling;	/* linkage in my parent's children list */
 	struct list_head thread_group;
 
 	/* PID hash table linkage. */
@@ -718,12 +721,7 @@ do {									\
 #define REMOVE_LINKS(p) do {				\
 	(p)->next_task->prev_task = (p)->prev_task;	\
 	(p)->prev_task->next_task = (p)->next_task;	\
-	if ((p)->p_osptr) \
-		(p)->p_osptr->p_ysptr = (p)->p_ysptr; \
-	if ((p)->p_ysptr) \
-		(p)->p_ysptr->p_osptr = (p)->p_osptr; \
-	else \
-		(p)->p_pptr->p_cptr = (p)->p_osptr; \
+	list_del_init(&(p)->sibling);			\
 	} while (0)
 
 #define SET_LINKS(p) do {					\
@@ -731,12 +729,33 @@ do {									\
 	(p)->prev_task = init_task.prev_task;			\
 	init_task.prev_task->next_task = (p);			\
 	init_task.prev_task = (p);				\
-	(p)->p_ysptr = NULL; \
-	if (((p)->p_osptr = (p)->p_pptr->p_cptr) != NULL) \
-		(p)->p_osptr->p_ysptr = p; \
-	(p)->p_pptr->p_cptr = p; \
+	list_add_tail(&(p)->sibling,&(p)->parent->children);	\
 	} while (0)
 
+static inline struct task_struct *eldest_child(struct task_struct *p)
+{
+	if (list_empty(&p->children)) return NULL;
+	return list_entry(p->children.next,struct task_struct,sibling);
+}
+
+static inline struct task_struct *youngest_child(struct task_struct *p)
+{
+	if (list_empty(&p->children)) return NULL;
+	return list_entry(p->children.prev,struct task_struct,sibling);
+}
+
+static inline struct task_struct *older_sibling(struct task_struct *p)
+{
+	if (p->sibling.prev==&p->parent->children) return NULL;
+	return list_entry(p->sibling.prev,struct task_struct,sibling);
+}
+
+static inline struct task_struct *younger_sibling(struct task_struct *p)
+{
+	if (p->sibling.next==&p->parent->children) return NULL;
+	return list_entry(p->sibling.next,struct task_struct,sibling);
+}
+
 #define for_each_task(p) \
 	for (p = &init_task ; (p = p->next_task) != &init_task ; )
 

kernel/exit.c

@@ -91,10 +91,10 @@ static int will_become_orphaned_pgrp(int pgrp, struct task_struct * ignored_task
 	for_each_task(p) {
 		if ((p == ignored_task) || (p->pgrp != pgrp) ||
 		    (p->state == TASK_ZOMBIE) ||
-		    (p->p_pptr->pid == 1))
+		    (p->parent->pid == 1))
 			continue;
-		if ((p->p_pptr->pgrp != pgrp) &&
-		    (p->p_pptr->session == p->session)) {
+		if ((p->parent->pgrp != pgrp) &&
+		    (p->parent->session == p->session)) {
 			read_unlock(&tasklist_lock);
  			return 0;
 		}
@@ -144,8 +144,8 @@ void reparent_to_init(void)
 
 	/* Reparent to init */
 	REMOVE_LINKS(current);
-	current->p_pptr = child_reaper;
-	current->p_opptr = child_reaper;
+	current->parent = child_reaper;
+	current->real_parent = child_reaper;
 	SET_LINKS(current);
 
 	/* Set the exit signal to SIGCHLD so we signal init on exit */
@@ -217,16 +217,16 @@ static inline void forget_original_parent(struct task_struct * father)
 		reaper = child_reaper;
 
 	for_each_task(p) {
-		if (p->p_opptr == father) {
+		if (p->real_parent == father) {
 			/* We dont want people slaying init */
 			p->exit_signal = SIGCHLD;
 			p->self_exec_id++;
 
 			/* Make sure we're not reparenting to ourselves */
 			if (p == reaper)
-				p->p_opptr = child_reaper;
+				p->real_parent = child_reaper;
 			else
-				p->p_opptr = reaper;
+				p->real_parent = reaper;
 
 			if (p->pdeath_signal) send_sig(p->pdeath_signal, p, 0);
 		}
@@ -400,7 +400,7 @@ static void exit_notify(void)
 	 * is about to become orphaned.
 	 */
 	 
-	t = current->p_pptr;
+	t = current->parent;
 	
 	if ((t->pgrp != current->pgrp) &&
 	    (t->session == current->session) &&
@@ -445,17 +445,12 @@ static void exit_notify(void)
 	write_lock_irq(&tasklist_lock);
 	current->state = TASK_ZOMBIE;
 	do_notify_parent(current, current->exit_signal);
-	while (current->p_cptr != NULL) {
-		p = current->p_cptr;
-		current->p_cptr = p->p_osptr;
-		p->p_ysptr = NULL;
+	while ((p = eldest_child(current))) {
+		list_del_init(&p->sibling);
 		p->ptrace = 0;
 
-		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;
+		p->parent = p->real_parent;
+		list_add_tail(&p->sibling,&p->parent->children);
 		if (p->state == TASK_ZOMBIE)
 			do_notify_parent(p, p->exit_signal);
 		/*
@@ -568,7 +563,9 @@ asmlinkage long sys_wait4(pid_t pid,unsigned int * stat_addr, int options, struc
 	tsk = current;
 	do {
 		struct task_struct *p;
-	 	for (p = tsk->p_cptr ; p ; p = p->p_osptr) {
+		struct list_head *_p;
+		list_for_each(_p,&tsk->children) {
+			p = list_entry(_p,struct task_struct,sibling);
 			if (pid>0) {
 				if (p->pid != pid)
 					continue;
@@ -613,10 +610,10 @@ asmlinkage long sys_wait4(pid_t pid,unsigned int * stat_addr, int options, struc
 				if (retval)
 					goto end_wait4; 
 				retval = p->pid;
-				if (p->p_opptr != p->p_pptr) {
+				if (p->real_parent != p->parent) {
 					write_lock_irq(&tasklist_lock);
 					REMOVE_LINKS(p);
-					p->p_pptr = p->p_opptr;
+					p->parent = p->real_parent;
 					SET_LINKS(p);
 					do_notify_parent(p, SIGCHLD);
 					write_unlock_irq(&tasklist_lock);

kernel/fork.c

@@ -666,7 +666,8 @@ int do_fork(unsigned long clone_flags, unsigned long stack_start,
 
 	INIT_LIST_HEAD(&p->run_list);
 
-	p->p_cptr = NULL;
+	INIT_LIST_HEAD(&p->children);
+	INIT_LIST_HEAD(&p->sibling);
 	init_waitqueue_head(&p->wait_chldexit);
 	p->vfork_done = NULL;
 	if (clone_flags & CLONE_VFORK) {
@@ -766,12 +767,12 @@ int do_fork(unsigned long clone_flags, unsigned long stack_start,
 	write_lock_irq(&tasklist_lock);
 
 	/* CLONE_PARENT re-uses the old parent */
-	p->p_opptr = current->p_opptr;
-	p->p_pptr = current->p_pptr;
+	p->real_parent = current->real_parent;
+	p->parent = current->parent;
 	if (!(clone_flags & CLONE_PARENT)) {
-		p->p_opptr = current;
+		p->real_parent = current;
 		if (!(p->ptrace & PT_PTRACED))
-			p->p_pptr = current;
+			p->parent = current;
 	}
 
 	if (clone_flags & CLONE_THREAD) {

kernel/ptrace.c

@@ -24,7 +24,7 @@ int ptrace_check_attach(struct task_struct *child, int kill)
 	if (!(child->ptrace & PT_PTRACED))
 		return -ESRCH;
 
-	if (child->p_pptr != current)
+	if (child->parent != current)
 		return -ESRCH;
 
 	if (!kill) {
@@ -70,9 +70,9 @@ int ptrace_attach(struct task_struct *task)
 	task_unlock(task);
 
 	write_lock_irq(&tasklist_lock);
-	if (task->p_pptr != current) {
+	if (task->parent != current) {
 		REMOVE_LINKS(task);
-		task->p_pptr = current;
+		task->parent = current;
 		SET_LINKS(task);
 	}
 	write_unlock_irq(&tasklist_lock);
@@ -98,7 +98,7 @@ int ptrace_detach(struct task_struct *child, unsigned int data)
 	child->exit_code = data;
 	write_lock_irq(&tasklist_lock);
 	REMOVE_LINKS(child);
-	child->p_pptr = child->p_opptr;
+	child->parent = child->real_parent;
 	SET_LINKS(child);
 	write_unlock_irq(&tasklist_lock);
 

kernel/sched.c

@@ -1320,6 +1320,7 @@ asmlinkage long sys_sched_rr_get_interval(pid_t pid, struct timespec *interval)
 static void show_task(task_t * p)
 {
 	unsigned long free = 0;
+	task_t *relative;
 	int state;
 	static const char * stat_nam[] = { "R", "S", "D", "Z", "T", "W" };
 
@@ -1346,17 +1347,17 @@ static void show_task(task_t * p)
 			n++;
 		free = (unsigned long) n - (unsigned long)(p+1);
 	}
-	printk("%5lu %5d %6d ", free, p->pid, p->p_pptr->pid);
-	if (p->p_cptr)
-		printk("%5d ", p->p_cptr->pid);
+	printk("%5lu %5d %6d ", free, p->pid, p->parent->pid);
+	if ((relative = eldest_child(p)))
+		printk("%5d ", relative->pid);
 	else
 		printk("      ");
-	if (p->p_ysptr)
-		printk("%7d", p->p_ysptr->pid);
+	if ((relative = younger_sibling(p)))
+		printk("%7d", relative->pid);
 	else
 		printk("       ");
-	if (p->p_osptr)
-		printk(" %5d", p->p_osptr->pid);
+	if ((relative = older_sibling(p)))
+		printk(" %5d", relative->pid);
 	else
 		printk("      ");
 	if (!p->mm)

kernel/signal.c

@@ -804,8 +804,8 @@ void do_notify_parent(struct task_struct *tsk, int sig)
 	info.si_code = why;
 	info.si_status = status;
 
-	send_sig_info(sig, &info, tsk->p_pptr);
-	wake_up_parent(tsk->p_pptr);
+	send_sig_info(sig, &info, tsk->parent);
+	wake_up_parent(tsk->parent);
 }
 
 

kernel/sys.c

@@ -839,7 +839,7 @@ asmlinkage long sys_setpgid(pid_t pid, pid_t pgid)
 	if (!p)
 		goto out;
 
-	if (p->p_pptr == current || p->p_opptr == current) {
+	if (p->parent == current || p->real_parent == current) {
 		err = -EPERM;
 		if (p->session != current->session)
 			goto out;

kernel/timer.c

@@ -742,14 +742,14 @@ asmlinkage long sys_getppid(void)
 	struct task_struct * me = current;
 	struct task_struct * parent;
 
-	parent = me->p_opptr;
+	parent = me->real_parent;
 	for (;;) {
 		pid = parent->pid;
 #if CONFIG_SMP
 {
 		struct task_struct *old = parent;
 		mb();
-		parent = me->p_opptr;
+		parent = me->real_parent;
 		if (old != parent)
 			continue;
 }