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

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Date:   Thu, 02 Nov 2017 16:45:51 +0000
From:   David Howells <dhowells@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     dhowells@...hat.com, 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

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?

David