Messages in this thread | | | Subject | Re: [patch 3/4] taskstats: Introduce cdata_acct for complete cumulative accounting | From | Michael Holzheu <> | Date | Thu, 25 Nov 2010 10:40:22 +0100 |
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Hello Oleg,
On Tue, 2010-11-23 at 17:59 +0100, Oleg Nesterov wrote: > On 11/19, Michael Holzheu wrote: > > TODO: > > ----- > > With this patch we take the siglock twice. First for the dead task > > and second for the parent of the dead task. This give the following > > lockdep warning (probably a lockdep annotation is needed here): > > And we already discussed this ;) We do not need 2 siglock's, only > parent's. Just move the callsite in __exit_signal() down, under > another (lockless) group_dead check. > > Or I missed something?
The problem with moving this down to the second group_dead check is that after __unhash_process() is called, pid_alive(tsk) which is checked in thread_group_cputime() returns false. Therefore we always get zero CPU times.
So I probably have to introduce a second group_dead check at the beginning of __exit_signal():
@@ -150,6 +153,9 @@ static void __exit_signal(struct task_st struct sighand_struct *sighand; struct tty_struct *uninitialized_var(tty);
+ if (group_dead) + __account_cdata(...); + sighand = rcu_dereference_check(tsk->sighand, rcu_read_lock_held() || > We can do this before taking ->siglock. Not that I think this really > matters, but otherwise this looks a bit confusing imho, as if we need > parent's ->siglock to pin something.
ok
> > > And thanks for splitting these changes. It was much, much easier to > read now.
My personal feeling is that probably the only acceptable thing would be to make the new behavior configurable with a sysctl and define the default as it currently is (POSIX compliant).
This would only introduce two additional checks in __exit_signal() and wait_task_zombie() and would not add any new fields to the signal_struct.
Michael
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