[v3,2/3] batman-adv: Remove unnecessary hardif_list_lock
Commit Message
hardif_list_lock is unneccessary because we already ensure that no
multiple admin operations can take place through rtnl_lock.
hardif_list_lock only adds additional overhead and complexity.
Critical functions now check whether they are called with rtnl_lock
using ASSERT_RTNL.
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
Rebased patch on top of "batman-adv: Make bat_priv->primary_if an rcu
protected pointer"
hard-interface.c | 21 ++++++---------------
1 files changed, 6 insertions(+), 15 deletions(-)
Comments
Looks quite good and seems to make sense to avoid the
double-locking. Tested it here and together with patch 1/3 fixes
the initial issue, too.
Just one minor thing:
----
[58518.225154] batman_adv: bat0: The MTU of interface eth1 is too
small (1500) to handle the transport of batman-adv packets.
Packets going over this interface will be fragmented on layer2
which could impact the performance. Setting the MTU to 1527 would
solve the problem.
[58518.278111] RTNL: assertion failed at
/home/mesh-node/incoming/batman-adv-git-builddir/hard-interface.c
(136)
[58518.293167] Pid: 6366, comm: bash Not tainted 2.6.38+ #4
[58518.299142] Call Trace:
[58518.300953] [<f8cb91f3>] primary_if_select+0x2f/0x9f
[batman_adv]
[58518.447844] [<f8cb8e9c>] ? rcu_read_unlock+0x1c/0x1e
[batman_adv]
[58518.452572] [<f8cb9146>] ? primary_if_get_selected+0x6a/0x71
[batman_adv]
[58518.455759] [<f8cb92c6>] hardif_activate_interface+0x63/0x91
[batman_adv]
[58518.459168] [<f8cb98e4>] hardif_enable_interface+0x1cc/0x21e
[batman_adv]
[58518.462481] [<f8cb7bca>] store_mesh_iface+0xed/0x113
[batman_adv]
[58518.465564] [<f8cb7add>] ? store_aggregated_ogms+0x28/0x28
[batman_adv]
[58518.468714] [<c11e1121>] kobj_attr_store+0x1a/0x22
[58518.472277] [<c11481dc>] sysfs_write_file+0xbc/0xe7
[58518.613128] [<c1148120>] ? sysfs_open_file+0x205/0x205
[58518.616400] [<c10ff7a7>] vfs_write+0x84/0xde
[58518.660437] [<c10ff89a>] sys_write+0x3b/0x60
[58518.667248] [<c151fd9d>] syscall_call+0x7/0xb
[58518.672117] batman_adv: bat0: Interface activated: eth1
----
So maybe it makes sense to add the assertion in
primary_if_select() in patch 3/3 instead?
Hmm, and I'm wondering if it might make sense to also document it
with a little comment above the struct list_head hardif_list;,
like:
/* List additions and deletions have to be rtnl_lock()'ed,
* list traversals just rcu-locked */
(or is that overdoing it?)
On Sat, Apr 30, 2011 at 10:54:14PM +0200, Sven Eckelmann wrote:
> hardif_list_lock is unneccessary because we already ensure that no
> multiple admin operations can take place through rtnl_lock.
> hardif_list_lock only adds additional overhead and complexity.
>
> Critical functions now check whether they are called with rtnl_lock
> using ASSERT_RTNL.
>
> Signed-off-by: Sven Eckelmann <sven@narfation.org>
> ---
> Rebased patch on top of "batman-adv: Make bat_priv->primary_if an rcu
> protected pointer"
>
>
> hard-interface.c | 21 ++++++---------------
> 1 files changed, 6 insertions(+), 15 deletions(-)
>
> diff --git a/hard-interface.c b/hard-interface.c
> index 6636d2f..7e2f772 100644
> --- a/hard-interface.c
> +++ b/hard-interface.c
> @@ -31,9 +31,6 @@
>
> #include <linux/if_arp.h>
>
> -/* protect update critical side of hardif_list - but not the content */
> -static DEFINE_SPINLOCK(hardif_list_lock);
> -
>
> static int batman_skb_recv(struct sk_buff *skb,
> struct net_device *dev,
> @@ -136,7 +133,7 @@ static void primary_if_select(struct bat_priv *bat_priv,
> struct hard_iface *curr_hard_iface;
> struct batman_packet *batman_packet;
>
> - spin_lock_bh(&hardif_list_lock);
> + ASSERT_RTNL();
>
> if (new_hard_iface && !atomic_inc_not_zero(&new_hard_iface->refcount))
> new_hard_iface = NULL;
> @@ -148,7 +145,7 @@ static void primary_if_select(struct bat_priv *bat_priv,
> hardif_free_ref(curr_hard_iface);
>
> if (!new_hard_iface)
> - goto out;
> + return;
>
> batman_packet = (struct batman_packet *)(new_hard_iface->packet_buff);
> batman_packet->flags = PRIMARIES_FIRST_HOP;
> @@ -161,9 +158,6 @@ static void primary_if_select(struct bat_priv *bat_priv,
> * our new primary interface
> */
> atomic_set(&bat_priv->hna_local_changed, 1);
> -
> -out:
> - spin_unlock_bh(&hardif_list_lock);
> }
>
> static bool hardif_is_iface_up(struct hard_iface *hard_iface)
> @@ -456,6 +450,8 @@ static struct hard_iface *hardif_add_interface(struct net_device *net_dev)
> struct hard_iface *hard_iface;
> int ret;
>
> + ASSERT_RTNL();
> +
> ret = is_valid_iface(net_dev);
> if (ret != 1)
> goto out;
> @@ -482,10 +478,7 @@ static struct hard_iface *hardif_add_interface(struct net_device *net_dev)
> atomic_set(&hard_iface->refcount, 2);
>
> check_known_mac_addr(hard_iface->net_dev);
> -
> - spin_lock(&hardif_list_lock);
> list_add_tail_rcu(&hard_iface->list, &hardif_list);
> - spin_unlock(&hardif_list_lock);
>
> return hard_iface;
>
> @@ -499,6 +492,8 @@ out:
>
> static void hardif_remove_interface(struct hard_iface *hard_iface)
> {
> + ASSERT_RTNL();
> +
> /* first deactivate interface */
> if (hard_iface->if_status != IF_NOT_IN_USE)
> hardif_disable_interface(hard_iface);
> @@ -516,13 +511,11 @@ void hardif_remove_interfaces(void)
> struct hard_iface *hard_iface, *hard_iface_tmp;
>
> rtnl_lock();
> - spin_lock(&hardif_list_lock);
> list_for_each_entry_safe(hard_iface, hard_iface_tmp,
> &hardif_list, list) {
> list_del_rcu(&hard_iface->list);
> hardif_remove_interface(hard_iface);
> }
> - spin_unlock(&hardif_list_lock);
> rtnl_unlock();
> }
>
> @@ -549,9 +542,7 @@ static int hard_if_event(struct notifier_block *this,
> hardif_deactivate_interface(hard_iface);
> break;
> case NETDEV_UNREGISTER:
> - spin_lock(&hardif_list_lock);
> list_del_rcu(&hard_iface->list);
> - spin_unlock(&hardif_list_lock);
>
> hardif_remove_interface(hard_iface);
> break;
> --
> 1.7.4.4
>
Linus Lüssing wrote:
> Looks quite good and seems to make sense to avoid the
> double-locking. Tested it here and together with patch 1/3 fixes
> the initial issue, too.
>
> Just one minor thing:
> ----
> [58518.225154] batman_adv: bat0: The MTU of interface eth1 is too
> small (1500) to handle the transport of batman-adv packets.
> Packets going over this interface will be fragmented on layer2
> which could impact the performance. Setting the MTU to 1527 would
> solve the problem.
> [58518.278111] RTNL: assertion failed at
> /home/mesh-node/incoming/batman-adv-git-builddir/hard-interface.c
> (136)
> [58518.293167] Pid: 6366, comm: bash Not tainted 2.6.38+ #4
> [58518.299142] Call Trace:
> [58518.300953] [<f8cb91f3>] primary_if_select+0x2f/0x9f
> [batman_adv]
> [58518.447844] [<f8cb8e9c>] ? rcu_read_unlock+0x1c/0x1e
> [batman_adv]
> [58518.452572] [<f8cb9146>] ? primary_if_get_selected+0x6a/0x71
> [batman_adv]
> [58518.455759] [<f8cb92c6>] hardif_activate_interface+0x63/0x91
> [batman_adv]
> [58518.459168] [<f8cb98e4>] hardif_enable_interface+0x1cc/0x21e
> [batman_adv]
> [58518.462481] [<f8cb7bca>] store_mesh_iface+0xed/0x113
> [batman_adv]
> [58518.465564] [<f8cb7add>] ? store_aggregated_ogms+0x28/0x28
> [batman_adv]
> [58518.468714] [<c11e1121>] kobj_attr_store+0x1a/0x22
> [58518.472277] [<c11481dc>] sysfs_write_file+0xbc/0xe7
> [58518.613128] [<c1148120>] ? sysfs_open_file+0x205/0x205
> [58518.616400] [<c10ff7a7>] vfs_write+0x84/0xde
> [58518.660437] [<c10ff89a>] sys_write+0x3b/0x60
> [58518.667248] [<c151fd9d>] syscall_call+0x7/0xb
> [58518.672117] batman_adv: bat0: Interface activated: eth1
> ----
>
> So maybe it makes sense to add the assertion in
> primary_if_select() in patch 3/3 instead?
No, the problem is that I changed the patch after I noticed that it wasn't
made for the current master - and only tested after all patches were applied.
I would like to add rtnl_lock/rtnl_unlock around primary_if_get_selected()
instead.
> Hmm, and I'm wondering if it might make sense to also document it
> with a little comment above the struct list_head hardif_list;,
> like:
> /* List additions and deletions have to be rtnl_lock()'ed,
> * list traversals just rcu-locked */
> (or is that overdoing it?)
Ok, will steal this comment from your mail - ok, change it slightly to present
it as my own work.
Kind regards,
Sven
@@ -31,9 +31,6 @@
#include <linux/if_arp.h>
-/* protect update critical side of hardif_list - but not the content */
-static DEFINE_SPINLOCK(hardif_list_lock);
-
static int batman_skb_recv(struct sk_buff *skb,
struct net_device *dev,
@@ -136,7 +133,7 @@ static void primary_if_select(struct bat_priv *bat_priv,
struct hard_iface *curr_hard_iface;
struct batman_packet *batman_packet;
- spin_lock_bh(&hardif_list_lock);
+ ASSERT_RTNL();
if (new_hard_iface && !atomic_inc_not_zero(&new_hard_iface->refcount))
new_hard_iface = NULL;
@@ -148,7 +145,7 @@ static void primary_if_select(struct bat_priv *bat_priv,
hardif_free_ref(curr_hard_iface);
if (!new_hard_iface)
- goto out;
+ return;
batman_packet = (struct batman_packet *)(new_hard_iface->packet_buff);
batman_packet->flags = PRIMARIES_FIRST_HOP;
@@ -161,9 +158,6 @@ static void primary_if_select(struct bat_priv *bat_priv,
* our new primary interface
*/
atomic_set(&bat_priv->hna_local_changed, 1);
-
-out:
- spin_unlock_bh(&hardif_list_lock);
}
static bool hardif_is_iface_up(struct hard_iface *hard_iface)
@@ -456,6 +450,8 @@ static struct hard_iface *hardif_add_interface(struct net_device *net_dev)
struct hard_iface *hard_iface;
int ret;
+ ASSERT_RTNL();
+
ret = is_valid_iface(net_dev);
if (ret != 1)
goto out;
@@ -482,10 +478,7 @@ static struct hard_iface *hardif_add_interface(struct net_device *net_dev)
atomic_set(&hard_iface->refcount, 2);
check_known_mac_addr(hard_iface->net_dev);
-
- spin_lock(&hardif_list_lock);
list_add_tail_rcu(&hard_iface->list, &hardif_list);
- spin_unlock(&hardif_list_lock);
return hard_iface;
@@ -499,6 +492,8 @@ out:
static void hardif_remove_interface(struct hard_iface *hard_iface)
{
+ ASSERT_RTNL();
+
/* first deactivate interface */
if (hard_iface->if_status != IF_NOT_IN_USE)
hardif_disable_interface(hard_iface);
@@ -516,13 +511,11 @@ void hardif_remove_interfaces(void)
struct hard_iface *hard_iface, *hard_iface_tmp;
rtnl_lock();
- spin_lock(&hardif_list_lock);
list_for_each_entry_safe(hard_iface, hard_iface_tmp,
&hardif_list, list) {
list_del_rcu(&hard_iface->list);
hardif_remove_interface(hard_iface);
}
- spin_unlock(&hardif_list_lock);
rtnl_unlock();
}
@@ -549,9 +542,7 @@ static int hard_if_event(struct notifier_block *this,
hardif_deactivate_interface(hard_iface);
break;
case NETDEV_UNREGISTER:
- spin_lock(&hardif_list_lock);
list_del_rcu(&hard_iface->list);
- spin_unlock(&hardif_list_lock);
hardif_remove_interface(hard_iface);
break;