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Date: Mon, 27 Oct 2014 20:53:39 +0100 From: Oleg Nesterov <oleg@...hat.com> To: Kirill Tkhai <ktkhai@...allels.com>, Peter Zijlstra <peterz@...radead.org> Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>, Vladimir Davydov <vdavydov@...allels.com>, Kirill Tkhai <tkhai@...dex.ru>, Christoph Lameter <cl@...ux.com> Subject: [PATCH 0/3] introduce task_rcu_dereference() Peter, let me repeat once again, if you still prefer to avoid probe_slab_address() and use SLAB_DESTROY_BY_RCU I won't argue. I do not like SLAB_DESTROY_BY_RCU in this particular case. With or without SDBR rq->curr can be reused and we need to avoid this race. The fact that with SDBR it can be reused only as another instance of task_struct is absolutely immaterial imo. Not to mention that SDBR still adds some overhead while probe_slab() is free unless CONFIG_DEBUG_PAGEALLOC, but this option adds a large slowdown anyway. However, my arguments against SDBR are not strictly technical, and I think that this falls into "maintainer is always right" category. So please tell me if you prefer v2 with SDBR. In this case 2/3 is not needed, and 3/3 can simply read ->sighand. Otherwise the code (and even the comments) will be the same. Compared to the draft patch I sent before - update the comments - do not use ERR_PTR(), just return the task or NULL, so kernel/sched/ doesn't need another helper. This means that task_rcu_dereference() does retry itself. We can add __task_rcu_dereference() if we have another which do not need/want to retry. Oleg. include/linux/sched.h | 1 + include/linux/uaccess.h | 30 +++++++++++++++------------- kernel/exit.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++ mm/slub.c | 6 +---- 4 files changed, 67 insertions(+), 19 deletions(-) -- 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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