Messages in this thread | | | Subject | Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier (v5) | From | Steven Rostedt <> | Date | Thu, 14 Jan 2010 13:52:12 -0500 |
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On Thu, 2010-01-14 at 13:37 -0500, Mathieu Desnoyers wrote:
> To make this painfully clear, I'll reorder the accesses to match that of > the CPU to memory: > > 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() > <buffered current = next> > <switch back to user-space> > urcu read lock() > access critical section data (3) > memory access before membarrier > <call sys_membarrier()> > smp_mb() > mm_cpumask includes CPU 1 > rcu_read_lock() > if (CPU 1 mm != our mm) > skip CPU 1.
I still don't see how the above conditional fails?
-- Steve
> rcu_read_unlock() > smp_mb() > <return to user-space> > memory access after membarrier > current = next (1) (buffer flush) > read gp > store local gp (2) > > This should make the problem a bit more evident. Access (3) is done > outside of the read-side C.S. as far as the userspace synchronize_rcu() > is concerned. > > Thanks, > > Mathieu > >
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