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Date: Tue, 07 Jun 2011 17:20:40 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Hillf Danton <dhillf@...il.com> Cc: LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu> Subject: Re: [PATCH] sched: correct testing need_resched in mutex_spin_on_owner() On Tue, 2011-06-07 at 22:47 +0800, Hillf Danton wrote: > Oh, it looks you are willing to rethink about testing need_resched? Dude, however did you come up with that deduction? mutex_spin_on_owner() does two things: - it validates that owner is in fact still running (if so it must be on another cpu, since we're running on this one). - it ensures we play nice and reschedule when we need to, so we don't hog our cpu. Testing TIF_NEED_RESCHED on owner like you propose is wrong because: - owner is not a stable pointer you can dereference, see owner_running(), you first need to validate that its still a valid pointer and then keep it valid while dereferencing it. - if owner were to reschedule, it would leave the cpu and we'd break out of the loop anyway by means of owner_running() failing, so its superfluous. Please, get a grip on reality and stop sending endless streams of patches based on wrong assumptions and mis-understandings. -- 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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