[PATCH RFC 12/13] exit: Delete write dependence on tasklist_lock in exit_notify()

[Kirill Tkhai <ktkhai@odin.com>]

Relatives and parent notifications have already protected by appropriate
kin_lock, so we may do not to take tasklist_lock for writing.

Hovewer, we still need it read locked to protect PGRP and PSID.

Signed-off-by: Kirill Tkhai <ktkhai@odin.com>
---
 kernel/exit.c   |   19 +++++++------------
 kernel/ptrace.c |    6 +++---
 2 files changed, 10 insertions(+), 15 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index aeded00..99d7aa3 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -460,8 +460,6 @@ static struct task_struct *find_alive_thread(struct task_struct *p)
 }
 
 static void check_pid_ns_reaper_exit(struct task_struct *father)
-	__releases(&tasklist_lock)
-	__acquires(&tasklist_lock)
 {
 	struct pid_namespace *pid_ns = task_active_pid_ns(father);
 	struct task_struct *reaper;
@@ -473,7 +471,7 @@ static void check_pid_ns_reaper_exit(struct task_struct *father)
 	if (likely(reaper != father))
 		return;
 
-	write_lock(&pid_ns->cr_lock);
+	write_lock_irq(&pid_ns->cr_lock);
 	read_real_parent_lock(father);
 
 	reaper = find_alive_thread(father);
@@ -481,18 +479,16 @@ static void check_pid_ns_reaper_exit(struct task_struct *father)
 		pid_ns->child_reaper = reaper;
 
 	read_real_parent_unlock(father);
-	write_unlock(&pid_ns->cr_lock);
+	write_unlock_irq(&pid_ns->cr_lock);
 
 	if (reaper)
 		return;
 
-	write_unlock_irq(&tasklist_lock);
 	if (unlikely(pid_ns == &init_pid_ns)) {
 		panic("Attempted to kill init! exitcode=0x%08x\n",
 			father->signal->group_exit_code ?: father->exit_code);
 	}
 	zap_pid_ns_processes(pid_ns);
-	write_lock_irq(&tasklist_lock);
 }
 
 /*
@@ -598,7 +594,6 @@ static void forget_original_parent(struct task_struct *father,
 	if (unlikely(!list_empty(&father->ptraced)))
 		exit_ptrace(father, dead);
 
-	/* Can drop and reacquire tasklist_lock */
 	check_pid_ns_reaper_exit(father);
 
 	/* read_lock() guarantees concurrent thread sees our PF_EXITING */
@@ -609,7 +604,7 @@ static void forget_original_parent(struct task_struct *father,
 	}
 	read_unlock(&father->kin_lock);
 
-	read_lock(&task_active_pid_ns(father)->cr_lock);
+	read_lock_irq(&task_active_pid_ns(father)->cr_lock);
 	reaper = find_double_lock_new_reaper(father);
 
 	list_for_each_entry(p, &father->children, sibling) {
@@ -632,7 +627,7 @@ static void forget_original_parent(struct task_struct *father,
 	list_splice_tail_init(&father->children, &reaper->children);
 
 	double_write_unlock(&reaper->kin_lock, &father->kin_lock);
-	read_unlock(&task_active_pid_ns(father)->cr_lock);
+	read_unlock_irq(&task_active_pid_ns(father)->cr_lock);
 }
 
 /*
@@ -645,12 +640,13 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
 	struct task_struct *p, *n;
 	LIST_HEAD(dead);
 
-	write_lock_irq(&tasklist_lock);
 	forget_original_parent(tsk, &dead);
 
+	read_lock_irq(&tasklist_lock);
 	write_parent_and_real_parent_lock(tsk);
 	if (group_dead)
 		kill_orphaned_pgrp(tsk->group_leader, NULL);
+	read_unlock(&tasklist_lock);
 
 	if (unlikely(tsk->ptrace)) {
 		int sig = thread_group_leader(tsk) &&
@@ -672,8 +668,7 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
 	/* mt-exec, de_thread() is waiting for group leader */
 	if (unlikely(tsk->signal->notify_count < 0))
 		wake_up_process(tsk->signal->group_exit_task);
-	write_parent_and_real_parent_unlock(tsk);
-	write_unlock_irq(&tasklist_lock);
+	write_parent_and_real_parent_unlock_irq(tsk);
 
 	list_for_each_entry_safe(p, n, &dead, ptrace_entry) {
 		list_del_init(&p->ptrace_entry);
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 6785f66..d6e2d0b 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -505,9 +505,9 @@ void exit_ptrace(struct task_struct *tracer, struct list_head *dead)
 		if (!p)
 			break;
 
-		write_parent_and_real_parent_lock(p);
+		write_parent_and_real_parent_lock_irq(p);
 		if (p->parent != tracer) {
-			write_parent_and_real_parent_unlock(p);
+			write_parent_and_real_parent_unlock_irq(p);
 			continue;
 		}
 
@@ -517,7 +517,7 @@ void exit_ptrace(struct task_struct *tracer, struct list_head *dead)
 		if (__ptrace_detach(tracer, p))
 			list_add(&p->ptrace_entry, dead);
 
-		write_parent_and_real_parent_unlock(p);
+		write_parent_and_real_parent_unlock_irq(p);
 	}
 	rcu_read_unlock();
 }