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ptrace children revamp

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ptrace no longer fiddles with the children/sibling links, and the
old ptrace_children list is gone.  Now ptrace, whether of one's own
children or another's via PTRACE_ATTACH, just uses the new ptraced
list instead.

There should be no user-visible difference that matters.  The only
change is the order in which do_wait() sees multiple stopped
children and stopped ptrace attachees.  Since wait_task_stopped()
was changed earlier so it no longer reorders the children list, we
already know this won't cause any new problems.

Signed-off-by: Roland McGrath <roland@redhat.com>
This commit is contained in:
Roland McGrath 2008-03-24 18:36:23 -07:00
parent 98abed0200
commit f470021adb
5 changed files with 163 additions and 142 deletions
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4
include/linux/init_task.h
View file

@ -140,8 +140,8 @@ extern struct group_info init_groups;
.nr_cpus_allowed = NR_CPUS, \
}, \
.tasks = LIST_HEAD_INIT(tsk.tasks), \
.ptrace_children= LIST_HEAD_INIT(tsk.ptrace_children), \
.ptrace_list = LIST_HEAD_INIT(tsk.ptrace_list), \
.ptraced = LIST_HEAD_INIT(tsk.ptraced), \
.ptrace_entry = LIST_HEAD_INIT(tsk.ptrace_entry), \
.real_parent = &tsk, \
.parent = &tsk, \
.children = LIST_HEAD_INIT(tsk.children), \

26
include/linux/sched.h
View file

@ -1062,12 +1062,6 @@ struct task_struct {
#endif
struct list_head tasks;
/*
* ptrace_list/ptrace_children forms the list of my children
* that were stolen by a ptracer.
*/
struct list_head ptrace_children;
struct list_head ptrace_list;
struct mm_struct *mm, *active_mm;
@ -1089,18 +1083,25 @@ struct task_struct {
/*
* pointers to (original) parent process, youngest child, younger sibling,
* older sibling, respectively. (p->father can be replaced with
* p->parent->pid)
* p->real_parent->pid)
*/
struct task_struct *real_parent; /* real parent process (when being debugged) */
struct task_struct *parent; /* parent process */
struct task_struct *real_parent; /* real parent process */
struct task_struct *parent; /* recipient of SIGCHLD, wait4() reports */
/*
* children/sibling forms the list of my children plus the
* tasks I'm ptracing.
* children/sibling forms the list of my natural children
*/
struct list_head children; /* list of my children */
struct list_head sibling; /* linkage in my parent's children list */
struct task_struct *group_leader; /* threadgroup leader */
/*
* ptraced is the list of tasks this task is using ptrace on.
* This includes both natural children and PTRACE_ATTACH targets.
* p->ptrace_entry is p's link on the p->parent->ptraced list.
*/
struct list_head ptraced;
struct list_head ptrace_entry;
/* PID/PID hash table linkage. */
struct pid_link pids[PIDTYPE_MAX];
struct list_head thread_group;
@ -1876,9 +1877,6 @@ extern void wait_task_inactive(struct task_struct * p);
#define wait_task_inactive(p) do { } while (0)
#endif
#define remove_parent(p) list_del_init(&(p)->sibling)
#define add_parent(p) list_add_tail(&(p)->sibling,&(p)->parent->children)
#define next_task(p) list_entry(rcu_dereference((p)->tasks.next), struct task_struct, tasks)
#define for_each_process(p) \

232
kernel/exit.c
View file

@ -71,7 +71,7 @@ static void __unhash_process(struct task_struct *p)
__get_cpu_var(process_counts)--;
}
list_del_rcu(&p->thread_group);
remove_parent(p);
list_del_init(&p->sibling);
}
/*
@ -152,6 +152,18 @@ static void delayed_put_task_struct(struct rcu_head *rhp)
put_task_struct(container_of(rhp, struct task_struct, rcu));
}
/*
* Do final ptrace-related cleanup of a zombie being reaped.
*
* Called with write_lock(&tasklist_lock) held.
*/
static void ptrace_release_task(struct task_struct *p)
{
BUG_ON(!list_empty(&p->ptraced));
ptrace_unlink(p);
BUG_ON(!list_empty(&p->ptrace_entry));
}
void release_task(struct task_struct * p)
{
struct task_struct *leader;
@ -160,8 +172,7 @@ repeat:
atomic_dec(&p->user->processes);
proc_flush_task(p);
write_lock_irq(&tasklist_lock);
ptrace_unlink(p);
BUG_ON(!list_empty(&p->ptrace_list) || !list_empty(&p->ptrace_children));
ptrace_release_task(p);
__exit_signal(p);
/*
@ -315,9 +326,8 @@ static void reparent_to_kthreadd(void)
ptrace_unlink(current);
/* Reparent to init */
remove_parent(current);
current->real_parent = current->parent = kthreadd_task;
add_parent(current);
list_move_tail(&current->sibling, &current->real_parent->children);
/* Set the exit signal to SIGCHLD so we signal init on exit */
current->exit_signal = SIGCHLD;
@ -692,37 +702,71 @@ static void exit_mm(struct task_struct * tsk)
mmput(mm);
}
static void
reparent_thread(struct task_struct *p, struct task_struct *father, int traced)
/*
* Detach all tasks we were using ptrace on.
* Any that need to be release_task'd are put on the @dead list.
*
* Called with write_lock(&tasklist_lock) held.
*/
static void ptrace_exit(struct task_struct *parent, struct list_head *dead)
{
struct task_struct *p, *n;
list_for_each_entry_safe(p, n, &parent->ptraced, ptrace_entry) {
__ptrace_unlink(p);
if (p->exit_state != EXIT_ZOMBIE)
continue;
/*
* If it's a zombie, our attachedness prevented normal
* parent notification or self-reaping. Do notification
* now if it would have happened earlier. If it should
* reap itself, add it to the @dead list. We can't call
* release_task() here because we already hold tasklist_lock.
*
* If it's our own child, there is no notification to do.
*/
if (!task_detached(p) && thread_group_empty(p)) {
if (!same_thread_group(p->real_parent, parent))
do_notify_parent(p, p->exit_signal);
}
if (task_detached(p)) {
/*
* Mark it as in the process of being reaped.
*/
p->exit_state = EXIT_DEAD;
list_add(&p->ptrace_entry, dead);
}
}
}
/*
* Finish up exit-time ptrace cleanup.
*
* Called without locks.
*/
static void ptrace_exit_finish(struct task_struct *parent,
struct list_head *dead)
{
struct task_struct *p, *n;
BUG_ON(!list_empty(&parent->ptraced));
list_for_each_entry_safe(p, n, dead, ptrace_entry) {
list_del_init(&p->ptrace_entry);
release_task(p);
}
}
static void reparent_thread(struct task_struct *p, struct task_struct *father)
{
if (p->pdeath_signal)
/* We already hold the tasklist_lock here. */
group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
/* Move the child from its dying parent to the new one. */
if (unlikely(traced)) {
/* Preserve ptrace links if someone else is tracing this child. */
list_del_init(&p->ptrace_list);
if (ptrace_reparented(p))
list_add(&p->ptrace_list, &p->real_parent->ptrace_children);
} else {
/* If this child is being traced, then we're the one tracing it
* anyway, so let go of it.
*/
p->ptrace = 0;
remove_parent(p);
p->parent = p->real_parent;
add_parent(p);
if (task_is_traced(p)) {
/*
* If it was at a trace stop, turn it into
* a normal stop since it's no longer being
* traced.
*/
ptrace_untrace(p);
}
}
list_move_tail(&p->sibling, &p->real_parent->children);
/* If this is a threaded reparent there is no need to
* notify anyone anything has happened.
@ -737,7 +781,8 @@ reparent_thread(struct task_struct *p, struct task_struct *father, int traced)
/* If we'd notified the old parent about this child's death,
* also notify the new parent.
*/
if (!traced && p->exit_state == EXIT_ZOMBIE &&
if (!ptrace_reparented(p) &&
p->exit_state == EXIT_ZOMBIE &&
!task_detached(p) && thread_group_empty(p))
do_notify_parent(p, p->exit_signal);
@ -754,12 +799,15 @@ reparent_thread(struct task_struct *p, struct task_struct *father, int traced)
static void forget_original_parent(struct task_struct *father)
{
struct task_struct *p, *n, *reaper = father;
struct list_head ptrace_dead;
INIT_LIST_HEAD(&ptrace_dead);
LIST_HEAD(ptrace_dead);
write_lock_irq(&tasklist_lock);
/*
* First clean up ptrace if we were using it.
*/
ptrace_exit(father, &ptrace_dead);
do {
reaper = next_thread(reaper);
if (reaper == father) {
@ -768,58 +816,19 @@ static void forget_original_parent(struct task_struct *father)
}
} while (reaper->flags & PF_EXITING);
/*
* There are only two places where our children can be:
*
* - in our child list
* - in our ptraced child list
*
* Search them and reparent children.
*/
list_for_each_entry_safe(p, n, &father->children, sibling) {
int ptrace;
ptrace = p->ptrace;
/* if father isn't the real parent, then ptrace must be enabled */
BUG_ON(father != p->real_parent && !ptrace);
if (father == p->real_parent) {
/* reparent with a reaper, real father it's us */
p->real_parent = reaper;
reparent_thread(p, father, 0);
} else {
/* reparent ptraced task to its real parent */
__ptrace_unlink (p);
if (p->exit_state == EXIT_ZOMBIE && !task_detached(p) &&
thread_group_empty(p))
do_notify_parent(p, p->exit_signal);
}
/*
* if the ptraced child is a detached zombie we must collect
* it before we exit, or it will remain zombie forever since
* we prevented it from self-reap itself while it was being
* traced by us, to be able to see it in wait4.
*/
if (unlikely(ptrace && p->exit_state == EXIT_ZOMBIE && task_detached(p)))
list_add(&p->ptrace_list, &ptrace_dead);
}
list_for_each_entry_safe(p, n, &father->ptrace_children, ptrace_list) {
p->real_parent = reaper;
reparent_thread(p, father, 1);
if (p->parent == father) {
BUG_ON(p->ptrace);
p->parent = p->real_parent;
}
reparent_thread(p, father);
}
write_unlock_irq(&tasklist_lock);
BUG_ON(!list_empty(&father->children));
BUG_ON(!list_empty(&father->ptrace_children));
list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_list) {
list_del_init(&p->ptrace_list);
release_task(p);
}
ptrace_exit_finish(father, &ptrace_dead);
}
/*
@ -1180,13 +1189,6 @@ static int eligible_child(enum pid_type type, struct pid *pid, int options,
return 0;
}
/*
* Do not consider detached threads that are
* not ptraced:
*/
if (task_detached(p) && !p->ptrace)
return 0;
/* Wait for all children (clone and not) if __WALL is set;
* otherwise, wait for clone children *only* if __WCLONE is
* set; otherwise, wait for non-clone children *only*. (Note:
@ -1399,7 +1401,7 @@ static int wait_task_zombie(struct task_struct *p, int options,
* the lock and this task is uninteresting. If we return nonzero, we have
* released the lock and the system call should return.
*/
static int wait_task_stopped(struct task_struct *p,
static int wait_task_stopped(int ptrace, struct task_struct *p,
int options, struct siginfo __user *infop,
int __user *stat_addr, struct rusage __user *ru)
{
@ -1407,7 +1409,7 @@ static int wait_task_stopped(struct task_struct *p,
uid_t uid = 0; /* unneeded, required by compiler */
pid_t pid;
if (!(p->ptrace & PT_PTRACED) && !(options & WUNTRACED))
if (!(options & WUNTRACED))
return 0;
exit_code = 0;
@ -1416,7 +1418,7 @@ static int wait_task_stopped(struct task_struct *p,
if (unlikely(!task_is_stopped_or_traced(p)))
goto unlock_sig;
if (!(p->ptrace & PT_PTRACED) && p->signal->group_stop_count > 0)
if (!ptrace && p->signal->group_stop_count > 0)
/*
* A group stop is in progress and this is the group leader.
* We won't report until all threads have stopped.
@ -1445,7 +1447,7 @@ unlock_sig:
*/
get_task_struct(p);
pid = task_pid_vnr(p);
why = (p->ptrace & PT_PTRACED) ? CLD_TRAPPED : CLD_STOPPED;
why = ptrace ? CLD_TRAPPED : CLD_STOPPED;
read_unlock(&tasklist_lock);
if (unlikely(options & WNOWAIT))
@ -1536,7 +1538,7 @@ static int wait_task_continued(struct task_struct *p, int options,
* Returns zero if the search for a child should continue;
* then *@notask_error is 0 if @p is an eligible child, or still -ECHILD.
*/
static int wait_consider_task(struct task_struct *parent,
static int wait_consider_task(struct task_struct *parent, int ptrace,
struct task_struct *p, int *notask_error,
enum pid_type type, struct pid *pid, int options,
struct siginfo __user *infop,
@ -1546,6 +1548,15 @@ static int wait_consider_task(struct task_struct *parent,
if (ret <= 0)
return ret;
if (likely(!ptrace) && unlikely(p->ptrace)) {
/*
* This child is hidden by ptrace.
* We aren't allowed to see it now, but eventually we will.
*/
*notask_error = 0;
return 0;
}
if (p->exit_state == EXIT_DEAD)
return 0;
@ -1562,7 +1573,8 @@ static int wait_consider_task(struct task_struct *parent,
*notask_error = 0;
if (task_is_stopped_or_traced(p))
return wait_task_stopped(p, options, infop, stat_addr, ru);
return wait_task_stopped(ptrace, p, options,
infop, stat_addr, ru);
return wait_task_continued(p, options, infop, stat_addr, ru);
}
@ -1583,11 +1595,16 @@ static int do_wait_thread(struct task_struct *tsk, int *notask_error,
struct task_struct *p;
list_for_each_entry(p, &tsk->children, sibling) {
int ret = wait_consider_task(tsk, p, notask_error,
type, pid, options,
infop, stat_addr, ru);
if (ret)
return ret;
/*
* Do not consider detached threads.
*/
if (!task_detached(p)) {
int ret = wait_consider_task(tsk, 0, p, notask_error,
type, pid, options,
infop, stat_addr, ru);
if (ret)
return ret;
}
}
return 0;
@ -1601,21 +1618,16 @@ static int ptrace_do_wait(struct task_struct *tsk, int *notask_error,
struct task_struct *p;
/*
* If we never saw an eligile child, check for children stolen by
* ptrace. We don't leave -ECHILD in *@notask_error if there are any,
* because we will eventually be allowed to wait for them again.
* Traditionally we see ptrace'd stopped tasks regardless of options.
*/
if (!*notask_error)
return 0;
options |= WUNTRACED;
list_for_each_entry(p, &tsk->ptrace_children, ptrace_list) {
int ret = eligible_child(type, pid, options, p);
if (unlikely(ret < 0))
list_for_each_entry(p, &tsk->ptraced, ptrace_entry) {
int ret = wait_consider_task(tsk, 1, p, notask_error,
type, pid, options,
infop, stat_addr, ru);
if (ret)
return ret;
if (ret) {
*notask_error = 0;
return 0;
}
}
return 0;

6
kernel/fork.c
View file

@ -1125,8 +1125,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
*/
p->group_leader = p;
INIT_LIST_HEAD(&p->thread_group);
INIT_LIST_HEAD(&p->ptrace_children);
INIT_LIST_HEAD(&p->ptrace_list);
INIT_LIST_HEAD(&p->ptrace_entry);
INIT_LIST_HEAD(&p->ptraced);
/* Now that the task is set up, run cgroup callbacks if
* necessary. We need to run them before the task is visible
@ -1198,7 +1198,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
}
if (likely(p->pid)) {
add_parent(p);
list_add_tail(&p->sibling, &p->real_parent->children);
if (unlikely(p->ptrace & PT_PTRACED))
__ptrace_link(p, current->parent);

37
kernel/ptrace.c
View file

@ -33,13 +33,9 @@
*/
void __ptrace_link(struct task_struct *child, struct task_struct *new_parent)
{
BUG_ON(!list_empty(&child->ptrace_list));
if (child->parent == new_parent)
return;
list_add(&child->ptrace_list, &child->parent->ptrace_children);
remove_parent(child);
BUG_ON(!list_empty(&child->ptrace_entry));
list_add(&child->ptrace_entry, &new_parent->ptraced);
child->parent = new_parent;
add_parent(child);
}
/*
@ -73,12 +69,8 @@ void __ptrace_unlink(struct task_struct *child)
BUG_ON(!child->ptrace);
child->ptrace = 0;
if (ptrace_reparented(child)) {
list_del_init(&child->ptrace_list);
remove_parent(child);
child->parent = child->real_parent;
add_parent(child);
}
child->parent = child->real_parent;
list_del_init(&child->ptrace_entry);
if (task_is_traced(child))
ptrace_untrace(child);
@ -492,15 +484,34 @@ int ptrace_traceme(void)
/*
* Are we already being traced?
*/
repeat:
task_lock(current);
if (!(current->ptrace & PT_PTRACED)) {
/*
* See ptrace_attach() comments about the locking here.
*/
unsigned long flags;
if (!write_trylock_irqsave(&tasklist_lock, flags)) {
task_unlock(current);
do {
cpu_relax();
} while (!write_can_lock(&tasklist_lock));
goto repeat;
}
ret = security_ptrace(current->parent, current,
PTRACE_MODE_ATTACH);
/*
* Set the ptrace bit in the process ptrace flags.
* Then link us on our parent's ptraced list.
*/
if (!ret)
if (!ret) {
current->ptrace |= PT_PTRACED;
__ptrace_link(current, current->real_parent);
}
write_unlock_irqrestore(&tasklist_lock, flags);
}
task_unlock(current);
return ret;