Messages in this thread | | | Date | Wed, 4 Feb 2009 14:19:01 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2/2] posix-cpu-timers: use ->sighand instead of ->signal to check the task is alive |
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On 02/04, Peter Zijlstra wrote: > > On Wed, 2009-02-04 at 00:17 +0100, Oleg Nesterov wrote: > > Sadly, it is not trivial to audit kernel/posix-cpu-timers.c, but it really > > abuses tasklist_lock. I believe it doesn't need this lock at all, but the > > changes are not easy to test. > > It uses that to hold of task reaping so ->signal doesn't go away.
Yes sure, but ->siglock alone is enough (this was not true when this code was written, as far as I know). It is not trivial to remove tasklist completely, but some places are trivial.
> If we make ->signal refcountable, and rcu freed along with the tasks I > think we can get away without tasklist_lock.
I think this is possible even without this change (which is good anyway). But the problem is not only that ->signal can go away. For example, posix_cpu_timer_set/posix_cpu_timer_schedule should not proceed if the task was already released, even if it had the valid ->signal.
Oleg.
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