From 7b1c6154fa8bb937e0b1b4f2adbb315d70270f10 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 26 Jun 2006 00:26:08 -0700 Subject: [PATCH] [PATCH] coredump: don't take tasklist_lock This patch removes tasklist_lock from zap_threads(). This is safe wrt: do_exit: The caller holds mm->mmap_sem. This means that task which shares the same ->mm can't pass exit_mm(), so it can't be unhashed from init_task.tasks or ->thread_group lists. fork: None of sub-threads can fork after zap_process(leader). All processes which were created before this point should be visible to zap_threads() because copy_process() adds the new process to the tail of init_task.tasks list, and ->siglock lock/unlock provides a memory barrier. de_thread: It does list_replace_rcu(&leader->tasks, ¤t->tasks). So zap_threads() will see either old or new leader, it does not matter. However, it can change p->sighand, so we should use lock_task_sighand() in zap_process(). Signed-off-by: Oleg Nesterov Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/exec.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index b58ba7d127e..49fa0127a33 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1373,7 +1373,11 @@ static void zap_process(struct task_struct *start) struct task_struct *t; unsigned long flags; - spin_lock_irqsave(&start->sighand->siglock, flags); + /* + * start->sighand can't disappear, but may be + * changed by de_thread() + */ + lock_task_sighand(start, &flags); start->signal->flags = SIGNAL_GROUP_EXIT; start->signal->group_stop_count = 0; @@ -1386,7 +1390,7 @@ static void zap_process(struct task_struct *start) } } while ((t = next_thread(t)) != start); - spin_unlock_irqrestore(&start->sighand->siglock, flags); + unlock_task_sighand(start, &flags); } static void zap_threads(struct mm_struct *mm) @@ -1404,7 +1408,7 @@ static void zap_threads(struct mm_struct *mm) complete(vfork_done); } - read_lock(&tasklist_lock); + rcu_read_lock(); for_each_process(g) { p = g; do { @@ -1415,7 +1419,7 @@ static void zap_threads(struct mm_struct *mm) } } while ((p = next_thread(p)) != g); } - read_unlock(&tasklist_lock); + rcu_read_unlock(); } static void coredump_wait(struct mm_struct *mm)