Messages in this thread | | | Date | Mon, 22 Oct 2012 10:25:42 -0700 | Subject | Re: Process Hang in __read_seqcount_begin | From | Peter LaDow <> |
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On Mon, Oct 22, 2012 at 10:01 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > This looks like a corruption of s->sequence, and is value is odd, even > if no writer is alive. > > Does local_bh_disable() disables preemption on RT ?
Hmmm....
With PREEMPT_RT_FULL defined (as we have):
void local_bh_disable(void) { migrate_disable(); current->softirq_nestcnt++; }
And the RT patches add the following:
#ifdef CONFIG_PREEMPT_RT_FULL # define preempt_disable_rt() preempt_disable() # define preempt_enable_rt() preempt_enable() # define preempt_disable_nort() do { } while (0) # define preempt_enable_nort() do { } while (0) # ifdef CONFIG_SMP extern void migrate_disable(void); extern void migrate_enable(void); # else /* CONFIG_SMP */ # define migrate_disable() do { } while (0) # define migrate_enable() do { } while (0) # endif /* CONFIG_SMP */ #else # define preempt_disable_rt() do { } while (0) # define preempt_enable_rt() do { } while (0) # define preempt_disable_nort() preempt_disable() # define preempt_enable_nort() preempt_enable() # define migrate_disable() preempt_disable() # define migrate_enable() preempt_enable() #endif
And since we are not SMP, local_bh_disable() essentially does nothing. These definitions are consistent across all the RT patches, up to 3.6.2-rt4 (as far as I can tell).
Now, is preemption required to be disabled in non-SMP systems?
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