Linux Ethernet Bridging - May 2020 - [Bridge] [PATCH net] net: bridge: vlan: Add a schedule point during VLAN processing

From: Ido Schimmel <idosch at mellanox.com>

User space can request to delete a range of VLANs from a bridge slave in
one netlink request. For each deleted VLAN the FDB needs to be traversed
in order to flush all the affected entries.

If a large range of VLANs is deleted and the number of FDB entries is
large or the FDB lock is contented, it is possible for the kernel to
loop through the deleted VLANs for a long time. In case preemption is
disabled, this can result in a soft lockup.

Fix this by adding a schedule point after each VLAN is deleted to yield
the CPU, if needed. This is safe because the VLANs are traversed in
process context.

Fixes: bdced7ef7838 ("bridge: support for multiple vlans and vlan ranges in
setlink and dellink requests")
Signed-off-by: Ido Schimmel <idosch at mellanox.com>
Reported-by: Stefan Priebe - Profihost AG <s.priebe at profihost.ag>
Tested-by: Stefan Priebe - Profihost AG <s.priebe at profihost.ag>
---
 net/bridge/br_netlink.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index 43dab4066f91..a0f5dbee8f9c 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -612,6 +612,7 @@ int br_process_vlan_info(struct net_bridge *br,
 					       v - 1, rtm_cmd);
 				v_change_start = 0;
 			}
+			cond_resched();
 		}
 		/* v_change_start is set only if the last/whole range changed */
 		if (v_change_start)
-- 
2.24.1

On 30/04/2020 22:38, Ido Schimmel wrote:
> From: Ido Schimmel <idosch at mellanox.com>
> 
> User space can request to delete a range of VLANs from a bridge slave in
> one netlink request. For each deleted VLAN the FDB needs to be traversed
> in order to flush all the affected entries.
> 
> If a large range of VLANs is deleted and the number of FDB entries is
> large or the FDB lock is contented, it is possible for the kernel to
> loop through the deleted VLANs for a long time. In case preemption is
> disabled, this can result in a soft lockup.
> 
> Fix this by adding a schedule point after each VLAN is deleted to yield
> the CPU, if needed. This is safe because the VLANs are traversed in
> process context.
> 
> Fixes: bdced7ef7838 ("bridge: support for multiple vlans and vlan
ranges in setlink and dellink requests")
> Signed-off-by: Ido Schimmel <idosch at mellanox.com>
> Reported-by: Stefan Priebe - Profihost AG <s.priebe at profihost.ag>
> Tested-by: Stefan Priebe - Profihost AG <s.priebe at profihost.ag>
> ---
>  net/bridge/br_netlink.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
> index 43dab4066f91..a0f5dbee8f9c 100644
> --- a/net/bridge/br_netlink.c
> +++ b/net/bridge/br_netlink.c
> @@ -612,6 +612,7 @@ int br_process_vlan_info(struct net_bridge *br,
>  					       v - 1, rtm_cmd);
>  				v_change_start = 0;
>  			}
> +			cond_resched();
>  		}
>  		/* v_change_start is set only if the last/whole range changed */
>  		if (v_change_start)
> 
Looks good, thanks!
Acked-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com>

From: Ido Schimmel <idosch at idosch.org>
Date: Thu, 30 Apr 2020 22:38:45 +0300
> From: Ido Schimmel <idosch at mellanox.com>
> 
> User space can request to delete a range of VLANs from a bridge slave in
> one netlink request. For each deleted VLAN the FDB needs to be traversed
> in order to flush all the affected entries.
> 
> If a large range of VLANs is deleted and the number of FDB entries is
> large or the FDB lock is contented, it is possible for the kernel to
> loop through the deleted VLANs for a long time. In case preemption is
> disabled, this can result in a soft lockup.
> 
> Fix this by adding a schedule point after each VLAN is deleted to yield
> the CPU, if needed. This is safe because the VLANs are traversed in
> process context.
> 
> Fixes: bdced7ef7838 ("bridge: support for multiple vlans and vlan
ranges in setlink and dellink requests")
> Signed-off-by: Ido Schimmel <idosch at mellanox.com>
> Reported-by: Stefan Priebe - Profihost AG <s.priebe at profihost.ag>
> Tested-by: Stefan Priebe - Profihost AG <s.priebe at profihost.ag>
Applied and queued up for -stable.