Re: [path][rfc] add PR_DETACH prctl command [3/3]
From: Stas Sergeev
Date: Tue Apr 19 2011 - 10:54:40 EST
The attached patch implements the PR_DETACH prctl
command. It detaches the entire process group from
its parent, allowing the parent to still read the detach
code with normal wait(). If the process then exits, the
notification of the new parent is delayed till the old parent
does either wait() to read the detach code, or exits.
commit c95ea73afce29a9c47bab29787d6eb014a8de9e6
Author: Stas <stas@stas.(none)>
Date: Mon Apr 11 15:06:33 2011 +0400
implement PR_DETACH
diff --git a/include/asm-generic/siginfo.h b/include/asm-generic/siginfo.h
index 942d30b..1da9c20 100644
--- a/include/asm-generic/siginfo.h
+++ b/include/asm-generic/siginfo.h
@@ -218,7 +218,8 @@ typedef struct siginfo {
#define CLD_TRAPPED (__SI_CHLD|4) /* traced child has trapped */
#define CLD_STOPPED (__SI_CHLD|5) /* child has stopped */
#define CLD_CONTINUED (__SI_CHLD|6) /* stopped child has continued */
-#define NSIGCHLD 6
+#define CLD_DETACHED (__SI_CHLD|7) /* child has detached */
+#define NSIGCHLD 7
/*
* SIGPOLL si_codes
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index caa151f..fdf71a9 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -158,6 +158,8 @@ extern struct cred init_cred;
.parent = &tsk, \
.children = LIST_HEAD_INIT(tsk.children), \
.sibling = LIST_HEAD_INIT(tsk.sibling), \
+ .detached_children = LIST_HEAD_INIT(tsk.detached_children),\
+ .detached_sibling = LIST_HEAD_INIT(tsk.detached_sibling), \
.group_leader = &tsk, \
RCU_INIT_POINTER(.real_cred, &init_cred), \
RCU_INIT_POINTER(.cred, &init_cred), \
diff --git a/include/linux/prctl.h b/include/linux/prctl.h
index a3baeb2..fbd2451 100644
--- a/include/linux/prctl.h
+++ b/include/linux/prctl.h
@@ -102,4 +102,6 @@
#define PR_MCE_KILL_GET 34
+#define PR_DETACH 35
+
#endif /* _LINUX_PRCTL_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index e74882f..c8a1741 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1260,6 +1260,9 @@ struct task_struct {
/* task state */
int exit_state;
int exit_code, exit_signal;
+ int detach_code;
+ int detaching;
+ int is_detaching:1;
int pdeath_signal; /* The signal sent when the parent dies */
/* ??? */
unsigned int personality;
@@ -1292,6 +1295,8 @@ struct task_struct {
*/
struct list_head children; /* list of my children */
struct list_head sibling; /* linkage in my parent's children list */
+ struct list_head detached_children; /* list of my detached children */
+ struct list_head detached_sibling; /* linkage in my parent's detached children list */
struct task_struct *group_leader; /* threadgroup leader */
/*
diff --git a/kernel/exit.c b/kernel/exit.c
index 2aa64e8..a2c5cfb 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -69,6 +69,7 @@ static void __unhash_process(struct task_struct *p, bool group_dead)
list_del_rcu(&p->tasks);
list_del_init(&p->sibling);
+ list_del_init(&p->detached_sibling);
__this_cpu_dec(process_counts);
}
list_del_rcu(&p->thread_group);
@@ -804,6 +805,17 @@ static void forget_original_parent(struct task_struct *father)
} while_each_thread(p, t);
reparent_leader(father, p, &dead_children);
}
+ list_for_each_entry_safe(p, n, &father->detached_children,
+ detached_sibling) {
+ int signal;
+ p->detaching = 0;
+ p->is_detaching = 0;
+ list_del_init(&p->detached_sibling);
+ if (p->exit_state == EXIT_ZOMBIE) {
+ signal = do_notify_parent(p, SIGCHLD);
+ BUG_ON(signal == DEATH_REAP);
+ }
+ }
write_unlock_irq(&tasklist_lock);
BUG_ON(!list_empty(&father->children));
@@ -858,7 +870,8 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
tsk->exit_signal = SIGCHLD;
signal = tracehook_notify_death(tsk, &cookie, group_dead);
- if (signal >= 0)
+ /* delay parent notification for detaching tasks */
+ if (signal >= 0 && !tsk->is_detaching)
signal = do_notify_parent(tsk, signal);
tsk->exit_state = signal == DEATH_REAP ? EXIT_DEAD : EXIT_ZOMBIE;
@@ -1507,6 +1520,54 @@ static int wait_task_continued(struct wait_opts *wo, struct task_struct *p)
return retval;
}
+static int wait_task_detached(struct wait_opts *wo, struct task_struct *p)
+{
+ int dt, signal, retval = 0;
+ pid_t pid;
+ uid_t uid;
+
+ if (!likely(wo->wo_flags & WEXITED))
+ return 0;
+
+ if (unlikely(wo->wo_flags & WNOWAIT)) {
+ get_task_struct(p);
+ read_unlock(&tasklist_lock);
+ pid = task_pid_vnr(p);
+ uid = __task_cred(p)->uid;
+ return wait_noreap_copyout(wo, p, pid, uid, CLD_DETACHED,
+ p->detach_code >> 8);
+ }
+
+ dt = xchg(&p->detaching, 0);
+ if (dt != 1)
+ return 0;
+ get_task_struct(p);
+ read_unlock(&tasklist_lock);
+
+ write_lock_irq(&tasklist_lock);
+ list_del_init(&p->detached_sibling);
+ if (p->exit_state == EXIT_ZOMBIE) {
+ signal = do_notify_parent(p, SIGCHLD);
+ BUG_ON(signal == DEATH_REAP);
+ }
+ p->is_detaching = 0;
+ write_unlock_irq(&tasklist_lock);
+
+ if (wo->wo_stat)
+ retval = put_user(p->detach_code, wo->wo_stat);
+
+ if (!retval) {
+ pid = task_pid_vnr(p);
+ uid = __task_cred(p)->uid;
+ retval = wait_noreap_copyout(wo, p, pid, uid, CLD_DETACHED,
+ p->detach_code >> 8);
+ } else {
+ put_task_struct(p);
+ }
+
+ return retval;
+}
+
static int can_wait_task_common(struct wait_opts *wo, struct task_struct *p)
{
int ret = eligible_child(wo, p);
@@ -1572,7 +1633,8 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
/*
* We don't reap group leaders with subthreads.
*/
- if (p->exit_state == EXIT_ZOMBIE && !delay_group_leader(p))
+ if (p->exit_state == EXIT_ZOMBIE && !delay_group_leader(p) &&
+ !p->is_detaching)
return wait_task_zombie(wo, p);
/*
@@ -1610,6 +1672,15 @@ static int do_wait_thread(struct wait_opts *wo, struct task_struct *tsk)
return ret;
}
+ list_for_each_entry(p, &tsk->detached_children, detached_sibling) {
+ ret = can_wait_task(wo, p);
+ if (!ret)
+ continue;
+ ret = wait_task_detached(wo, p);
+ if (ret)
+ return ret;
+ }
+
return 0;
}
diff --git a/kernel/fork.c b/kernel/fork.c
index 25e4291..feadef7 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1070,6 +1070,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
copy_flags(clone_flags, p);
INIT_LIST_HEAD(&p->children);
INIT_LIST_HEAD(&p->sibling);
+ INIT_LIST_HEAD(&p->detached_children);
+ INIT_LIST_HEAD(&p->detached_sibling);
rcu_copy_process(p);
p->vfork_done = NULL;
spin_lock_init(&p->alloc_lock);
@@ -1233,6 +1235,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
p->pdeath_signal = 0;
p->exit_state = 0;
+ p->detaching = 0;
+ p->is_detaching = 0;
/*
* Ok, make it visible to the rest of the system.
diff --git a/kernel/sys.c b/kernel/sys.c
index 18da702..1d88ee8 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -28,6 +28,7 @@
#include <linux/suspend.h>
#include <linux/tty.h>
#include <linux/signal.h>
+#include <linux/tracehook.h>
#include <linux/cn_proc.h>
#include <linux/getcpu.h>
#include <linux/task_io_accounting_ops.h>
@@ -1736,6 +1737,41 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
else
error = PR_MCE_KILL_DEFAULT;
break;
+ case PR_DETACH: {
+ struct task_struct *p, *leader;
+ int notif;
+ struct pid_namespace *pid_ns = task_active_pid_ns(me);
+ error = -EPERM;
+ /* not detaching from init */
+ if (same_thread_group(me->real_parent,
+ pid_ns->child_reaper))
+ break;
+ if (arg2 & ~0x7f)
+ break;
+ write_lock_irq(&tasklist_lock);
+ leader = me->group_leader;
+ leader->detach_code = arg2 << 8;
+ notif = do_signal_parent(leader, leader->exit_signal,
+ CLD_DETACHED, arg2);
+ if (notif != DEATH_REAP) {
+ list_add_tail(&leader->detached_sibling,
+ &leader->real_parent->detached_children);
+ leader->detaching = 1;
+ leader->is_detaching = 1;
+ }
+ p = leader;
+ do {
+ if (!task_ptrace(p))
+ p->parent = pid_ns->child_reaper;
+ p->real_parent = pid_ns->child_reaper;
+ } while_each_thread(leader, p);
+ list_move_tail(&leader->sibling,
+ &leader->real_parent->children);
+ leader->exit_signal = SIGCHLD;
+ write_unlock_irq(&tasklist_lock);
+ error = 0;
+ break;
+ }
default:
error = -EINVAL;
break;