Re: [PATCH net] net: core: synchronize link-watch when carrier is queried

[Jiri Pirko <jiri@resnulli.us>]

Mon, Dec 04, 2023 at 09:47:07PM CET, johannes@sipsolutions.net wrote:
>From: Johannes Berg <johannes.berg@intel.com>
>
>There are multiple ways to query for the carrier state: through
>rtnetlink, sysfs, and (possibly) ethtool. Synchronize linkwatch
>work before these operations so that we don't have a situation
>where userspace queries the carrier state between the driver's
>carrier off->on transition and linkwatch running and expects it
>to work, when really (at least) TX cannot work until linkwatch
>has run.
>
>I previously posted a longer explanation of how this applies to
>wireless [1] but with this wireless can simply query the state
>before sending data, to ensure the kernel is ready for it.
>
>[1] https://lore.kernel.org/all/346b21d87c69f817ea3c37caceb34f1f56255884.camel@sipsolutions.net/
>
>Signed-off-by: Johannes Berg <johannes.berg@intel.com>
>---
> include/linux/netdevice.h | 9 +++++++++
> net/core/dev.c            | 2 +-
> net/core/dev.h            | 1 -
> net/core/link_watch.c     | 2 +-
> net/core/net-sysfs.c      | 8 +++++++-
> net/core/rtnetlink.c      | 8 ++++++++
> net/ethtool/ioctl.c       | 3 +++
> 7 files changed, 29 insertions(+), 4 deletions(-)
>
>diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>index 2564e209465e..17dbaf379c69 100644
>--- a/include/linux/netdevice.h
>+++ b/include/linux/netdevice.h
>@@ -4195,6 +4195,15 @@ static inline void netdev_ref_replace(struct net_device *odev,
>  */
> void linkwatch_fire_event(struct net_device *dev);
> 
>+/**
>+ * linkwatch_sync_dev - sync linkwatch for the given device
>+ * @dev: network device to sync linkwatch for
>+ *
>+ * Sync linkwatch for the given device, removing it from the
>+ * pending work list (if queued).
>+ */
>+void linkwatch_sync_dev(struct net_device *dev);
>+
> /**
>  *	netif_carrier_ok - test if carrier present
>  *	@dev: network device
>diff --git a/net/core/dev.c b/net/core/dev.c
>index c879246be48d..188799b2c6a5 100644
>--- a/net/core/dev.c
>+++ b/net/core/dev.c
>@@ -10511,7 +10511,7 @@ void netdev_run_todo(void)
> 		write_lock(&dev_base_lock);
> 		dev->reg_state = NETREG_UNREGISTERED;
> 		write_unlock(&dev_base_lock);
>-		linkwatch_forget_dev(dev);
>+		linkwatch_sync_dev(dev);
> 	}
> 
> 	while (!list_empty(&list)) {
>diff --git a/net/core/dev.h b/net/core/dev.h
>index 5aa45f0fd4ae..cb06fe5e38ea 100644
>--- a/net/core/dev.h
>+++ b/net/core/dev.h
>@@ -30,7 +30,6 @@ int __init dev_proc_init(void);
> #endif
> 
> void linkwatch_init_dev(struct net_device *dev);
>-void linkwatch_forget_dev(struct net_device *dev);
> void linkwatch_run_queue(void);
> 
> void dev_addr_flush(struct net_device *dev);
>diff --git a/net/core/link_watch.c b/net/core/link_watch.c
>index ed3e5391fa79..7be5b3ab32bd 100644
>--- a/net/core/link_watch.c
>+++ b/net/core/link_watch.c
>@@ -240,7 +240,7 @@ static void __linkwatch_run_queue(int urgent_only)
> 	spin_unlock_irq(&lweventlist_lock);
> }
> 
>-void linkwatch_forget_dev(struct net_device *dev)
>+void linkwatch_sync_dev(struct net_device *dev)
> {
> 	unsigned long flags;
> 	int clean = 0;
>diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
>index fccaa5bac0ed..d9b33e923b18 100644
>--- a/net/core/net-sysfs.c
>+++ b/net/core/net-sysfs.c
>@@ -194,8 +194,14 @@ static ssize_t carrier_show(struct device *dev,
> {
> 	struct net_device *netdev = to_net_dev(dev);
> 
>-	if (netif_running(netdev))
>+	if (netif_running(netdev)) {
>+		/* Synchronize carrier state with link watch,
>+		 * see also rtnl_getlink().
>+		 */
>+		linkwatch_sync_dev(netdev);
>+
> 		return sysfs_emit(buf, fmt_dec, !!netif_carrier_ok(netdev));
>+	}
> 
> 	return -EINVAL;
> }
>diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
>index e8431c6c8490..613268d7c491 100644
>--- a/net/core/rtnetlink.c
>+++ b/net/core/rtnetlink.c
>@@ -3853,6 +3853,14 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr *nlh,
> 	if (nskb == NULL)
> 		goto out;
> 
>+	/* Synchronize the carrier state so we don't report a state
>+	 * that we're not actually going to honour immediately; if
>+	 * the driver just did a carrier off->on transition, we can
>+	 * only TX if link watch work has run, but without this we'd
>+	 * already report carrier on, even if it doesn't work yet.
>+	 */

This comment is a bit harder to understand for me, but I eventually did
get it :)

Patch looks fine to me.

Reviewed-by: Jiri Pirko <jiri@nvidia.com>



>+	linkwatch_sync_dev(dev);
>+
> 	err = rtnl_fill_ifinfo(nskb, dev, net,
> 			       RTM_NEWLINK, NETLINK_CB(skb).portid,
> 			       nlh->nlmsg_seq, 0, 0, ext_filter_mask,
>diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
>index 0b0ce4f81c01..a977f8903467 100644
>--- a/net/ethtool/ioctl.c
>+++ b/net/ethtool/ioctl.c
>@@ -58,6 +58,9 @@ static struct devlink *netdev_to_devlink_get(struct net_device *dev)
> 
> u32 ethtool_op_get_link(struct net_device *dev)
> {
>+	/* Synchronize carrier state with link watch, see also rtnl_getlink() */
>+	linkwatch_sync_dev(dev);
>+
> 	return netif_carrier_ok(dev) ? 1 : 0;
> }
> EXPORT_SYMBOL(ethtool_op_get_link);
>-- 
>2.43.0
>
>