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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <AANLkTin3JoNQ4_A3eXBAW148kEqWSxr06rY5h8yH+BGb@mail.gmail.com>
Date:	Tue, 14 Dec 2010 15:33:03 -0800
From:	Mike Waychison <mikew@...gle.com>
To:	Michał Mirosław <mirqus@...il.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 Michał Mirosław <mirqus@...il.com>:
> 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?

The target_list_lock protects the list, as well as the state
transitions.  This makes iterating through the list and getting a
consistent view of the targets a lot easier when it comes time to
transmitting packets we are guaranteed that nobody is changing the
target state underneath us if nt->np_state == NETPOLL_ENABLED while we
hold the lock.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html