Messages in this thread |  | | | Subject | Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier (v5) | | From | Steven Rostedt <> | | Date | Thu, 14 Jan 2010 13:50:37 -0500 |
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On Thu, 2010-01-14 at 12:54 -0500, Mathieu Desnoyers wrote: > * Peter Zijlstra (peterz@infradead.org) wrote: > > On Thu, 2010-01-14 at 11:26 -0500, Mathieu Desnoyers wrote: > > > > > It's this scenario that is causing problem. Let's consider this > > > execution: > > > > > (slightly augmented) > > CPU 0 (membarrier) CPU 1 (another mm -> our mm) > <user-space> > <kernel-space> > switch_mm() > smp_mb() > clear_mm_cpumask() > set_mm_cpumask() > smp_mb() (by load_cr3() on x86) > switch_to() > memory access before membarrier > <call sys_membarrier()> > smp_mb() > mm_cpumask includes CPU 1 > rcu_read_lock() > if (CPU 1 mm != our mm)
But here, CPU 1 updated its mm already and did a smp_mb, won't that make us send the smp_mb anyway?
-- Steve
> skip CPU 1. > rcu_read_unlock() > smp_mb() > <return to user-space> > current = next (1) > <switch back to user-space> > urcu read lock() > read gp > store local gp (2) > barrier() > access critical section data (3) > memory access after membarrier
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