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[PATCH] coredump: don't take tasklist_lock

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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, &current->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 <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Oleg Nesterov 2006-06-26 00:26:08 -07:00 committed by Linus Torvalds
parent d5f70c00ad
commit 7b1c6154fa
1 changed files with 8 additions and 4 deletions
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12
fs/exec.c
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@ -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)