linux-kernel - Re: [PATCH] Pass mode to wait_on_atomic_t() action funcs and provide default actions

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Message-ID: <20171102164808.zelswfla2coczmhy@hirez.programming.kicks-ass.net>
Date:   Thu, 2 Nov 2017 17:48:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Pass mode to wait_on_atomic_t() action funcs and provide
 default actions

On Thu, Nov 02, 2017 at 04:45:51PM +0000, David Howells wrote:
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > > The moment atomic_dec_and_test() is called, *net is at liberty to disappear,
> > > so there's no way to find a waitqueue - unless that waitqueue is guaranteed
> > > not to be deallocated, eg. by being global.
> > 
> > But any possible wait side will still need to dereference *net at an
> > indeterminate point in the future to ascertain the value does now indeed
> > read 0.
> 
> Yeah, the assumption is that the *wait* side is where the deallocation is
> happening.  So I have something like:
> 
> 	net->live = false; // Tell the cell managers to delete the cells
> 	...
> 	foreach (cell)
> 		queue_work(cell);
> 	...
> 	wait_on_atomic_t(&net->cells_outstanding, atomic_t_wait,
> 			 TASK_UNINTERRUPTIBLE);
> 	...
> 	destroy(net);
> 
> > ... We can certainly start with your patch, as that does clean things up.
> 
> Can I put that down as a Grudgingly-acked-by?

Yeah sure ;-)