From 77e4ef99d1c596a31747668e5fd837f77b6349b6 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 12 Dec 2011 18:12:21 -0800 Subject: threadgroup: extend threadgroup_lock() to cover exit and exec threadgroup_lock() protected only protected against new addition to the threadgroup, which was inherently somewhat incomplete and problematic for its only user cgroup. On-going migration could race against exec and exit leading to interesting problems - the symmetry between various attach methods, task exiting during method execution, ->exit() racing against attach methods, migrating task switching basic properties during exec and so on. This patch extends threadgroup_lock() such that it protects against all three threadgroup altering operations - fork, exit and exec. For exit, threadgroup_change_begin/end() calls are added to exit_signals around assertion of PF_EXITING. For exec, threadgroup_[un]lock() are updated to also grab and release cred_guard_mutex. With this change, threadgroup_lock() guarantees that the target threadgroup will remain stable - no new task will be added, no new PF_EXITING will be set and exec won't happen. The next patch will update cgroup so that it can take full advantage of this change. -v2: beefed up comment as suggested by Frederic. -v3: narrowed scope of protection in exit path as suggested by Frederic. Signed-off-by: Tejun Heo Reviewed-by: KAMEZAWA Hiroyuki Acked-by: Li Zefan Acked-by: Frederic Weisbecker Cc: Oleg Nesterov Cc: Andrew Morton Cc: Paul Menage Cc: Linus Torvalds --- kernel/signal.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'kernel/signal.c') diff --git a/kernel/signal.c b/kernel/signal.c index b3f78d09a10..399c184bf0a 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2359,8 +2359,15 @@ void exit_signals(struct task_struct *tsk) int group_stop = 0; sigset_t unblocked; + /* + * @tsk is about to have PF_EXITING set - lock out users which + * expect stable threadgroup. + */ + threadgroup_change_begin(tsk); + if (thread_group_empty(tsk) || signal_group_exit(tsk->signal)) { tsk->flags |= PF_EXITING; + threadgroup_change_end(tsk); return; } @@ -2370,6 +2377,9 @@ void exit_signals(struct task_struct *tsk) * see wants_signal(), do_signal_stop(). */ tsk->flags |= PF_EXITING; + + threadgroup_change_end(tsk); + if (!signal_pending(tsk)) goto out; -- cgit v1.2.3