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Date: Mon, 01 Feb 2010 11:24:37 -0500 From: Steven Rostedt <rostedt@...dmis.org> To: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Nicholas Miell <nmiell@...cast.net>, laijs@...fujitsu.com, dipankar@...ibm.com, josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org, Valdis.Kletnieks@...edu, dhowells@...hat.com Subject: Re: [patch 2/3] scheduler: add full memory barriers upon task switch at runqueue lock/unlock On Mon, 2010-02-01 at 11:09 -0500, Mathieu Desnoyers wrote: > We can deal with the rq->cur update by holding the rq lock in each > iteration of the for_each_cpu(cpu, mm_cpumask(current->mm)) loop. This > ensures that if rq->cur is updated, we have an associated memory barrier > issued (e.g. on x86, implied by writing to cr3 while the rq lock is held). > > However, this does not deal with mm_cpumask update, and we cannot use > the per-cpu rq lock, as it's a process-wide data structure updated with > clear_bit/set_bit in switch_mm(). So at the very least, we would have to > add memory barriers in switch_mm() on some architectures to deal with > this. > Doesn't set_bit imply a wmb()? If so couldn't we do: What about: again: tmp_mask = mm_cpumask(current->mm); smp_mb(); rcu_read_lock(); /* ensures validity of cpu_curr(cpu) tasks */ for_each_cpu(cpu, tmp_mask) { spin_lock_irq(&cpu_rq(cpu)->lock); ret = current->mm == cpu_curr(cpu)->mm; spin_unlock_irq(&cpu_rq(cpu)->lock); if (ret) smp_call_function_single(cpu, membarrier_ipi, NULL, 1); } rcu_read_unlock(); smp_mb(); if (tmp_mask != mm_cpumask(current->mm)) { /* do check for signals here */ goto again; } Would the above work? -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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