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Date: Fri, 17 Dec 2010 15:52:38 -0500
From: Neil Horman <nhorman@...driver.com>
To: Mike Waychison <mikew@...gle.com>
Cc: simon.kagstrom@...insight.net, davem@...emloft.net,
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
On Tue, Dec 14, 2010 at 01:29:10PM -0800, Mike Waychison wrote:
> Representing the internal state within netconsole isn't really a boolean
> value, but rather a state machine with transitions.
>
> This patch introduces 4 states that the netconsole multi-target can
> handle. These states are:
> - NETPOLL_DISABLED:
> The netpoll structure hasn't been setup.
> - NETPOLL_SETTINGUP:
> The netpoll structure is being setup, and only whoever set this
> state can transition out of it. Must come from the NETPOLL_DISABLED
> state.
> - NETPOLL_ENABLED:
> The netpoll structure has been setup and we are good to emit
> packets.
> - NETPOLL_CLEANING:
> Somebody is queued to call netpoll_clean. Whoever does so must
> transition out of this state. Must come from the NETPOLL_CLEANING
> state.
>
> The SETTINGUP state specifically targets the window where
> netpoll_setup() can take a while (for example, waiting on RTNL).
> During this window, we want to exclude console messages from being
> emitted to this netpoll target. We also want to exclude any subsequent
> user thread that tries to simultaneously enable or disable the target.
>
> The CLEANING state will be used in a subsequent patch to safely defer
> netpoll_cleanup to scheduled work in process context (to fix the
> deadlock that will occur whenever NETDEV_UNREGISTER is seen).
>
> When introducing these new transition states, it no longer makes sense
> to 'disable' the target if the interface is going down, only when it is
> being removed completely (or deslaved). In fact, prior to this change,
> we would leak a reference to the network device if an interface was
> brought down, the target removed, and netconsole unloaded.
>
> Signed-off-by: Mike Waychison <mikew@...gle.com>
> Acked-by: Matt Mackall <mpm@...enic.com>
> ---
> drivers/net/netconsole.c | 62 +++++++++++++++++++++++++++++-----------------
> 1 files changed, 39 insertions(+), 23 deletions(-)
>
> 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
> @@ -71,16 +71,24 @@ static LIST_HEAD(target_list);
> /* This needs to be a spinlock because write_msg() cannot sleep */
> static DEFINE_SPINLOCK(target_list_lock);
>
> +#define NETPOLL_DISABLED 0
> +#define NETPOLL_SETTINGUP 1
> +#define NETPOLL_ENABLED 2
> +#define NETPOLL_CLEANING 3
> +
> /**
> * struct netconsole_target - Represents a configured netconsole target.
> * @list: Links this target into the target_list.
> * @item: Links us into the configfs subsystem hierarchy.
> - * @enabled: On / off knob to enable / disable target.
> - * Visible from userspace (read-write).
> - * We maintain a strict 1:1 correspondence between this and
> - * whether the corresponding netpoll is active or inactive.
> + * @np_state: Enabled / Disabled / SettingUp / Cleaning
> + * Visible from userspace (read-write) as "enabled".
> + * We maintain a state machine here of the valid states. Either a
> + * target is enabled or disabled, but it may also be in a
> + * transitional state whereby nobody is allowed to act on the
> + * target other than whoever owns the transition.
> + *
> * Also, other parameters of a target may be modified at
> - * runtime only when it is disabled (enabled == 0).
> + * runtime only when it is disabled (np_state == NETPOLL_ENABLED).
> * @np: The netpoll structure for this target.
> * Contains the other userspace visible parameters:
> * dev_name (read-write)
> @@ -96,7 +104,7 @@ struct netconsole_target {
> #ifdef CONFIG_NETCONSOLE_DYNAMIC
> struct config_item item;
> #endif
> - int enabled;
> + int np_state;
> struct netpoll np;
> };
>
> @@ -189,7 +197,7 @@ static struct netconsole_target *alloc_param_target(char *target_config)
> if (err)
> goto fail;
>
> - nt->enabled = 1;
> + nt->np_state = NETPOLL_ENABLED;
>
> return nt;
>
> @@ -275,7 +283,8 @@ static long strtol10_check_range(const char *cp, long min, long max)
>
> static ssize_t show_enabled(struct netconsole_target *nt, char *buf)
> {
> - return snprintf(buf, PAGE_SIZE, "%d\n", nt->enabled);
> + return snprintf(buf, PAGE_SIZE, "%d\n",
> + nt->np_state == NETPOLL_ENABLED);
> }
>
> static ssize_t show_dev_name(struct netconsole_target *nt, char *buf)
> @@ -337,9 +346,12 @@ static ssize_t store_enabled(struct netconsole_target *nt,
>
> if (enabled) { /* 1 */
> spin_lock_irqsave(&target_list_lock, flags);
> - if (nt->enabled)
> + if (nt->np_state != NETPOLL_DISABLED)
> goto busy;
> - spin_unlock_irqrestore(&target_list_lock, flags);
> + else {
> + nt->np_state = NETPOLL_SETTINGUP;
> + spin_unlock_irqrestore(&target_list_lock, flags);
> + }
>
> /*
> * Skip netpoll_parse_options() -- all the attributes are
> @@ -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;
> @@ -360,10 +372,17 @@ static ssize_t store_enabled(struct netconsole_target *nt,
> printk(KERN_INFO "netconsole: network logging started\n");
> } else { /* 0 */
> spin_lock_irqsave(&target_list_lock, flags);
> - nt->enabled = 0;
> + if (nt->np_state == NETPOLL_ENABLED)
> + nt->np_state = NETPOLL_CLEANING;
> + else if (nt->np_state != NETPOLL_DISABLED)
> + goto busy;
> spin_unlock_irqrestore(&target_list_lock, flags);
>
> netpoll_cleanup(&nt->np);
> +
> + spin_lock_irqsave(&target_list_lock, flags);
> + nt->np_state = NETPOLL_DISABLED;
> + spin_unlock_irqrestore(&target_list_lock, flags);
> }
>
> return strnlen(buf, count);
> @@ -486,7 +505,7 @@ static ssize_t store_locked_##_name(struct netconsole_target *nt, \
> unsigned long flags; \
> ssize_t ret; \
> spin_lock_irqsave(&target_list_lock, flags); \
> - if (nt->enabled) { \
> + if (nt->np_state != NETPOLL_DISABLED) { \
> printk(KERN_ERR "netconsole: target (%s) is enabled, " \
> "disable to update parameters\n", \
> config_item_name(&nt->item)); \
> @@ -642,7 +661,7 @@ static void drop_netconsole_target(struct config_group *group,
> * The target may have never been enabled, or was manually disabled
> * before being removed so netpoll may have already been cleaned up.
> */
> - if (nt->enabled)
> + if (nt->np_state == NETPOLL_ENABLED)
> netpoll_cleanup(&nt->np);
>
> config_item_put(&nt->item);
> @@ -680,16 +699,17 @@ static int netconsole_netdev_event(struct notifier_block *this,
> struct net_device *dev = ptr;
>
> if (!(event == NETDEV_CHANGENAME || event == NETDEV_UNREGISTER ||
> - event == NETDEV_BONDING_DESLAVE || event == NETDEV_GOING_DOWN))
> + event == NETDEV_BONDING_DESLAVE))
> goto done;
>
> spin_lock_irqsave(&target_list_lock, flags);
> list_for_each_entry(nt, &target_list, list) {
> - if (nt->np.dev == dev) {
> + if (nt->np_state == NETPOLL_ENABLED && nt->np.dev == dev) {
> switch (event) {
> case NETDEV_CHANGENAME:
> strlcpy(nt->np.dev_name, dev->name, IFNAMSIZ);
> break;
> + case NETDEV_BONDING_DESLAVE:
> case NETDEV_UNREGISTER:
I don't follow what you're doing here. Previously NETDEV_BONDING_DESLAVE events
simply caused the netconsole interface to get deactivated, and now we're doing a
dev_put on the bonded interface bacause of the above move. Given that
NETDEV_BONDING_DESLAVE events are generated when a slave leaves the bond, this
doesn't seem right, or am I missing something
Regards
Neil
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