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Date: Wed, 01 Nov 2017 18:34:38 +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: > > I'd like to propose this change for the next merge window. One question, > > though: rather than providing an exported default function, should the > > default be used automatically if a NULL function pointer is passed? > > > > The default being atomic_t_wait? Yes. > FWIW, I think the whole wait_atomic_t thing is an utter piece of crap > that should be killed out right. It uses this hashed waitqueue crap and > does not in fact do anything with the variable that needs it to be > atomic_t. What would you replace it with? Bear in mind that the atomic_t may have been deallocated by the time wake_up_atomic_t() is called. I'm using it like: static void afs_dec_cells_outstanding(struct afs_net *net) { if (atomic_dec_and_test(&net->cells_outstanding)) wake_up_atomic_t(&net->cells_outstanding); } 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. David
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