Messages in this thread | | | Date | Thu, 23 Oct 2014 21:56:04 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v2 0/2] document ->sighand protection, rcu_read_unlock() deadlocks |
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Ping ;)
Paul, should I resend or you do not think this can go via your rcu tree?
On 09/28, Oleg Nesterov wrote: > > Paul, could you take these 2 doc patches? Assuming that you agree > with the comments, of course. > > On 09/24, Paul E. McKenney wrote: > > > > On Tue, Sep 23, 2014 at 09:03:48PM +0200, Oleg Nesterov wrote: > > > > > > Paul, will you agree if we turn it into > > > ... > > > /* > > > * On the succesfull return we hold ->siglock. According to comment > > > * above rcu_read_unlock() this is against the rules, but scheduler > > > * locks are fine under this lock, signal_wake_up() takes them too. > > > */ > > > rcu_read_unlock(); > > > > If you guys continue the guarantee of no deadlock, I am OK with this change. > > Heh. Contrary to what I said (and you all were agree ;), this deadlock > is actually possible, so we can not remove the deadlock-avoidance from > __lock_task_sighand(). And I do not see how we can cleanup this code > because preempt_disable() + spin_lock() is not -rt friendly. > > I think this deserves a bit of documentation, see 2/2. Perhaps this is > just me, but imo the current comment is a bit misleading. > > "if the caller of rcu_read_unlock() already holds one of these locks ..." > is not a problem in fact. I mean, pi_lock or rq->lock are special enough, > nobody should ever call the outermost rcu_read_unlock() with these locks > held. rt_mutex->wait_lock should be fine too, also because ->boost_mtx > is private to rcu_boost() and rcu_read_unlock_special(). > > But. They can race with each other, and that is why rcu_read_unlock() > under (say) ->siglock can actually lead to deadlock. And only because > rt_mutex->wait_lock doesn't disable irqs. Or I am totally confused. > > Perhaps we can change rtmutex.c to use raw_spin_lock_irqsave(), or do > something else... > > Oleg. > > include/linux/rcupdate.h | 4 +++- > kernel/fork.c | 5 ++++- > kernel/signal.c | 12 +++++++++++- > 3 files changed, 18 insertions(+), 3 deletions(-)
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