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    SubjectRe: [PATCH v3 03/22] netconsole: Introduce 'enabled' state-machine
    From
    2010/12/14 Mike Waychison <mikew@google.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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