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Subject[PATCH 09/16] netconsole: replace target_list_lock with console_lock
Date
netconsole has been using a spinlock - target_list_lock - to protect
the list of configured netconsole targets and their enable/disable
states. With the disabling from netdevice_notifier moved off to a
workqueue by the previous patch and thus outside of rtnl_lock,
target_list_lock can be replaced with console_lock, which allows us to
avoid grabbing an extra lock in the log write path and can simplify
locking when involving other subsystems as console_lock is only
trylocked from printk path.

This patch replaces target_list_lock with console_lock. The
conversion is one-to-one except for write_msg(). The function is
called with console_lock() already held so no further locking is
necessary; however, as netpoll_send_udp() expects irq to be disabled,
explicit irq save/restore pair is added around it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: David Miller <davem@davemloft.net>
---
drivers/net/netconsole.c | 50 ++++++++++++++++++------------------------------
1 file changed, 19 insertions(+), 31 deletions(-)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index d355776..57c02ab 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -73,12 +73,12 @@ static int __init option_setup(char *opt)
__setup("netconsole=", option_setup);
#endif /* MODULE */

-/* Linked list of all configured targets */
+/*
+ * Linked list of all configured targets. The list and each target's
+ * enable/disable state are protected by console_lock.
+ */
static LIST_HEAD(target_list);

-/* This needs to be a spinlock because write_msg() cannot sleep */
-static DEFINE_SPINLOCK(target_list_lock);
-
/**
* struct netconsole_target - Represents a configured netconsole target.
* @list: Links this target into the target_list.
@@ -325,7 +325,6 @@ static ssize_t store_enabled(struct netconsole_target *nt,
const char *buf,
size_t count)
{
- unsigned long flags;
int enabled;
int err;

@@ -357,9 +356,9 @@ static ssize_t store_enabled(struct netconsole_target *nt,
* otherwise we might end up in write_msg() with
* nt->np.dev == NULL and nt->enabled == true
*/
- spin_lock_irqsave(&target_list_lock, flags);
+ console_lock();
nt->enabled = false;
- spin_unlock_irqrestore(&target_list_lock, flags);
+ console_unlock();
netpoll_cleanup(&nt->np);
}

@@ -601,7 +600,6 @@ static struct config_item_type netconsole_target_type = {
static struct config_item *make_netconsole_target(struct config_group *group,
const char *name)
{
- unsigned long flags;
struct netconsole_target *nt;

nt = alloc_netconsole_target();
@@ -612,9 +610,9 @@ static struct config_item *make_netconsole_target(struct config_group *group,
config_item_init_type_name(&nt->item, name, &netconsole_target_type);

/* Adding, but it is disabled */
- spin_lock_irqsave(&target_list_lock, flags);
+ console_lock();
list_add(&nt->list, &target_list);
- spin_unlock_irqrestore(&target_list_lock, flags);
+ console_unlock();

return &nt->item;
}
@@ -622,12 +620,11 @@ static struct config_item *make_netconsole_target(struct config_group *group,
static void drop_netconsole_target(struct config_group *group,
struct config_item *item)
{
- unsigned long flags;
struct netconsole_target *nt = to_target(item);

- spin_lock_irqsave(&target_list_lock, flags);
+ console_lock();
list_del(&nt->list);
- spin_unlock_irqrestore(&target_list_lock, flags);
+ console_unlock();

/*
* The target may have never been enabled, or was manually disabled
@@ -664,11 +661,10 @@ static struct configfs_subsystem netconsole_subsys = {
static void netconsole_deferred_disable_work_fn(struct work_struct *work)
{
struct netconsole_target *nt, *to_disable;
- unsigned long flags;

repeat:
to_disable = NULL;
- spin_lock_irqsave(&target_list_lock, flags);
+ console_lock();
list_for_each_entry(nt, &target_list, list) {
if (!nt->disable_scheduled)
continue;
@@ -682,7 +678,7 @@ repeat:
to_disable = nt;
break;
}
- spin_unlock_irqrestore(&target_list_lock, flags);
+ console_unlock();

if (to_disable) {
netpoll_cleanup(&to_disable->np);
@@ -698,7 +694,6 @@ static DECLARE_WORK(netconsole_deferred_disable_work,
static int netconsole_netdev_event(struct notifier_block *this,
unsigned long event, void *ptr)
{
- unsigned long flags;
struct netconsole_target *nt;
struct net_device *dev = netdev_notifier_info_to_dev(ptr);
bool stopped = false;
@@ -707,7 +702,7 @@ static int netconsole_netdev_event(struct notifier_block *this,
event == NETDEV_RELEASE || event == NETDEV_JOIN))
goto done;

- spin_lock_irqsave(&target_list_lock, flags);
+ console_lock();
list_for_each_entry(nt, &target_list, list) {
if (nt->np.dev == dev) {
switch (event) {
@@ -726,7 +721,7 @@ static int netconsole_netdev_event(struct notifier_block *this,
}
}
}
- spin_unlock_irqrestore(&target_list_lock, flags);
+ console_unlock();
if (stopped) {
const char *msg = "had an event";
switch (event) {
@@ -755,7 +750,6 @@ static struct notifier_block netconsole_netdev_notifier = {
static void write_msg(struct console *con, const char *msg, unsigned int len)
{
int frag, left;
- unsigned long flags;
struct netconsole_target *nt;
const char *tmp;

@@ -765,9 +759,7 @@ static void write_msg(struct console *con, const char *msg, unsigned int len)
if (list_empty(&target_list))
return;

- spin_lock_irqsave(&target_list_lock, flags);
list_for_each_entry(nt, &target_list, list) {
- netconsole_target_get(nt);
if (nt->enabled && netif_running(nt->np.dev)) {
/*
* We nest this inside the for-each-target loop above
@@ -783,9 +775,7 @@ static void write_msg(struct console *con, const char *msg, unsigned int len)
left -= frag;
}
}
- netconsole_target_put(nt);
}
- spin_unlock_irqrestore(&target_list_lock, flags);
}

static struct console netconsole = {
@@ -798,7 +788,6 @@ static int __init init_netconsole(void)
{
int err;
struct netconsole_target *nt, *tmp;
- unsigned long flags;
char *target_config;
char *input = config;

@@ -812,9 +801,9 @@ static int __init init_netconsole(void)
/* Dump existing printks when we register */
netconsole.flags |= CON_PRINTBUFFER;

- spin_lock_irqsave(&target_list_lock, flags);
+ console_lock();
list_add(&nt->list, &target_list);
- spin_unlock_irqrestore(&target_list_lock, flags);
+ console_unlock();
}
}

@@ -839,8 +828,8 @@ fail:

/*
* Remove all targets and destroy them (only targets created
- * from the boot/module option exist here). Skipping the list
- * lock is safe here, and netpoll_cleanup() will sleep.
+ * from the boot/module option exist here). Skipping the console
+ * lock is safe here.
*/
list_for_each_entry_safe(nt, tmp, &target_list, list) {
list_del(&nt->list);
@@ -864,8 +853,7 @@ static void __exit cleanup_netconsole(void)
* and would first be rmdir(2)'ed from userspace. We reach
* here only when they are already destroyed, and only those
* created from the boot/module option are left, so remove and
- * destroy them. Skipping the list lock is safe here, and
- * netpoll_cleanup() will sleep.
+ * destroy them. Skipping the console lock is safe here.
*/
list_for_each_entry_safe(nt, tmp, &target_list, list) {
list_del(&nt->list);
--
2.1.0


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