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Date:   Sun, 16 Aug 2020 22:17:14 -0400
From:   Joel Fernandes <joel@joelfernandes.org>
To:     peterz@infradead.org
Cc:     linux-kernel@vger.kernel.org, Aaron Lu <aaron.lwe@gmail.com>,
        Aubrey Li <aubrey.li@linux.intel.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
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        Tim Chen <tim.c.chen@intel.com>,
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        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
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        Phil Auld <pauld@redhat.com>,
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        Paolo Bonzini <pbonzini@redhat.com>,
        Chen Yu <yu.c.chen@intel.com>,
        Christian Brauner <christian.brauner@ubuntu.com>
Subject: Re: [PATCH RFC 02/12] entry/idle: Add a common function for
 activites during idle entry/exit
Message-ID: <20200817021714.GB1492280@google.com>
References: <20200815031908.1015049-1-joel@joelfernandes.org>
 <20200815031908.1015049-3-joel@joelfernandes.org>
 <20200815081441.GG2674@hirez.programming.kicks-ass.net>
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Hello Peter,

On Sat, Aug 15, 2020 at 10:14:41AM +0200, peterz@infradead.org wrote:
> On Fri, Aug 14, 2020 at 11:18:58PM -0400, Joel Fernandes (Google) wrote:
> > Currently only RCU hooks for idle entry/exit are called. In later
> > patches, kernel-entry protection functionality will be added.
> > 
> > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> 
> NAK, rcu_idle_enter() is broken where it is now, it needs to be pushed
> in deeper:
> 
> http://lkml.kernel.org/r/20200807193017.962482579@infradead.org

Thank you for pointing it out. Not a huge problem, a couple ways I can do it:
1. Move the calls to sched_core_unsafe_{enter,exit}() deeper into the idle loop.
2. Keep the calls to sched_core_unsafe_{enter,exit}() where they are now as
   in this patch, but leave out the rcu_idle_{enter,exit}() calls alone so
   they can be moved deeper as you mentioned.

#1 is not necessary for these patches to work and might be overkill.

I'll go the #2 route then. Let me know any other ideas you might have.

What I am trying to do here is to handle a case where task is switching to
idle (say it went to sleep) and wakes up later.

usermode -> syscall (kernel mode - so mark unsafe) -> idle (mark safe).

idle -> syscall wakes (kernel mode - so mark unsafe) -> usermode (mark safe).

Thank you,

 - Joel