Messages in this thread | | | Date | Thu, 9 Jul 2015 11:42:49 +0300 | From | Dan Carpenter <> | Subject | Re: [PATCH RFC tip/core/rcu 05/14] rcu: Abstract sequence counting from synchronize_sched_expedited() |
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On Wed, Jul 01, 2015 at 03:18:04PM -0700, Paul E. McKenney wrote: > > > +/* Adjust sequence number for start of update-side operation. */ > > > +static void rcu_seq_start(unsigned long *sp) > > > +{ > > > + WRITE_ONCE(*sp, *sp + 1); > > > + smp_mb(); /* Ensure update-side operation after counter increment. */ > > > + WARN_ON_ONCE(!(*sp & 0x1)); > > > +} > > > > That wants to be an ACQUIRE, right? > > I cannot put the acquire in the WARN_ON_ONCE() because there > are configurations where WARN_ON_ONCE() is compiled out.
I think WARN_ON_ONCE() always evaulates the condition. You are maybe thinking of VM_WARN_ON_ONCE().
I'm on a different thread where we almost introduced a bug by using VM_WARN_ONCE() instead of WARN_ONCE(). The VM_WARNING conditions had long execute times so they are weird.
regards, dan carpenter
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