linux-kernel - Re: [RFC][PATCH] Fix a race between rwsem and the scheduler

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Message-ID: <20160831133104.GD10153@twins.programming.kicks-ass.net>
Date:   Wed, 31 Aug 2016 15:31:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Balbir Singh <bsingharora@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Nicholas Piggin <nicholas.piggin@...il.com>
Subject: Re: [RFC][PATCH] Fix a race between rwsem and the scheduler

On Wed, Aug 31, 2016 at 07:28:18AM +1000, Benjamin Herrenschmidt wrote:

> On powerpc we have a sync deep in _switch to achieve that.

OK, for giggles, could you (or Balbir) check what happens if you take
that sync out?

There should be enough serialization in the generic code to cover the
case that code mentions.

ARM64 has a stronger barrier in its context switch code, but that's
because they need to sync against external agents (like their TLB and
cache) and no amount of generic locking is going to cover that.