linux-kernel - Re: [PATCH v3 03/22] netconsole: Introduce 'enabled' state-machine

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Message-ID: <AANLkTik8wzDPPtMM+YPoOSojiW_Nev-KDkAg8dtDV=g1@mail.gmail.com>
Date:	Wed, 15 Dec 2010 00:21:53 +0100
From:	Michał Mirosław <mirqus@...il.com>
To:	Mike Waychison <mikew@...gle.com>
Cc:	simon.kagstrom@...insight.net, davem@...emloft.net,
	nhorman@...driver.com, Matt Mackall <mpm@...enic.com>,
	adurbin@...gle.com, linux-kernel@...r.kernel.org,
	chavey@...gle.com, Greg KH <greg@...ah.com>,
	netdev@...r.kernel.org,
	Américo Wang <xiyou.wangcong@...il.com>,
	akpm@...ux-foundation.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v3 03/22] netconsole: Introduce 'enabled' state-machine

2010/12/14 Mike Waychison <mikew@...gle.com>:
> Representing the internal state within netconsole isn't really a boolean
> value, but rather a state machine with transitions.
[...]
> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> index 6e16888..288a025 100644
> --- a/drivers/net/netconsole.c
> +++ b/drivers/net/netconsole.c
[...]
> @@ -350,9 +362,9 @@ static ssize_t store_enabled(struct netconsole_target *nt,
>                err = netpoll_setup(&nt->np);
>                spin_lock_irqsave(&target_list_lock, flags);
>                if (err)
> -                       nt->enabled = 0;
> +                       nt->np_state = NETPOLL_DISABLED;
>                else
> -                       nt->enabled = 1;
> +                       nt->np_state = NETPOLL_ENABLED;
>                spin_unlock_irqrestore(&target_list_lock, flags);
>                if (err)
>                        return err;
[...]

Since the spinlock protects only nt->np_state setting, you might be
able to remove it altogether and use cmpxchg() where nt->np_state
transitions from enabled or disabled state.

Maybe the locking scheme just needs more thought altogether?

Best Regards,
Michał Mirosław
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