[PATCH net-next v3 1/2] netpoll: Make netpoll_send_udp return status instead of void

[PATCH net-next v3 1/2] netpoll: Make netpoll_send_udp return status instead of void

[Maksym Kutsevol]

netpoll_send_udp can return if send was successful.
It will allow client code to be aware of the send status.

Possible return values are the result of __netpoll_send_skb (cast to int)
and -ENOMEM. This doesn't cover the case when TX was not successful
instantaneously and was scheduled for later, __netpoll__send_skb returns
success in that case.

Signed-off-by: Maksym Kutsevol <max@kutsevol.com>
---
Changelog:

 v3: No changes, resend.

 v2: No changes, resend.
  * https://lore.kernel.org/netdev/20240828214524.1867954-1-max@kutsevol.com/
 v1:
  * https://lore.kernel.org/netdev/20240824215130.2134153-1-max@kutsevol.com/

 include/linux/netpoll.h | 2 +-
 net/core/netpoll.c      | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index cd4e28db0cbd..b1ba8d6331a5 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -56,7 +56,7 @@ static inline void netpoll_poll_disable(struct net_device *dev) { return; }
 static inline void netpoll_poll_enable(struct net_device *dev) { return; }
 #endif
 
-void netpoll_send_udp(struct netpoll *np, const char *msg, int len);
+int netpoll_send_udp(struct netpoll *np, const char *msg, int len);
 void netpoll_print_options(struct netpoll *np);
 int netpoll_parse_options(struct netpoll *np, char *opt);
 int __netpoll_setup(struct netpoll *np, struct net_device *ndev);
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index ca52cbe0f63c..4719db36ff25 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -390,7 +390,7 @@ netdev_tx_t netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
 }
 EXPORT_SYMBOL(netpoll_send_skb);
 
-void netpoll_send_udp(struct netpoll *np, const char *msg, int len)
+int netpoll_send_udp(struct netpoll *np, const char *msg, int len)
 {
 	int total_len, ip_len, udp_len;
 	struct sk_buff *skb;
@@ -414,7 +414,7 @@ void netpoll_send_udp(struct netpoll *np, const char *msg, int len)
 	skb = find_skb(np, total_len + np->dev->needed_tailroom,
 		       total_len - len);
 	if (!skb)
-		return;
+		return -ENOMEM;
 
 	skb_copy_to_linear_data(skb, msg, len);
 	skb_put(skb, len);
@@ -490,7 +490,7 @@ void netpoll_send_udp(struct netpoll *np, const char *msg, int len)
 
 	skb->dev = np->dev;
 
-	netpoll_send_skb(np, skb);
+	return (int)netpoll_send_skb(np, skb);
 }
 EXPORT_SYMBOL(netpoll_send_udp);
 

base-commit: bf73478b539b4a13e0b4e104c82fe3c2833db562
-- 
2.43.5

[PATCH net-next v3 2/2] netcons: Add udp send fail statistics to netconsole

[Maksym Kutsevol]

Enhance observability of netconsole. Packet sends can fail.
Start tracking at least two failure possibilities: ENOMEM and
NET_XMIT_DROP for every target. Stats are exposed via an additional
attribute in CONFIGFS.

The exposed statistics allows easier debugging of cases when netconsole
messages were not seen by receivers, eliminating the guesswork if the
sender thinks that messages in question were sent out.

Stats are not reset on enable/disable/change remote ip/etc, they
belong to the netcons target itself.

Reported-by: Breno Leitao <leitao@debian.org>
Closes: https://lore.kernel.org/all/ZsWoUzyK5du9Ffl+@gmail.com/
Signed-off-by: Maksym Kutsevol <max@kutsevol.com>
---
Changelog:
v3:
 * cleanup the accidental slip of debugging addons.
 * use IS_ENABLED() instead of #ifdef. Always have stats field.

v2:
 * https://lore.kernel.org/netdev/20240828214524.1867954-2-max@kutsevol.com/
 * fixed commit message wording and reported-by reference.
 * not hiding netconsole_target_stats when CONFIG_NETCONSOLE_DYNAMIC
   is not enabled.
 * rename stats attribute in configfs to transmit_errors and make it
   a single u64 value, which is a sum of errors that occured.
 * make a wrapper function to count errors instead of a return result
   classifier one.
 * use u64_stats_sync.h to manage stats.

v1:
 * https://lore.kernel.org/netdev/20240824215130.2134153-2-max@kutsevol.com/

 Documentation/networking/netconsole.rst |  5 ++-
 drivers/net/netconsole.c                | 60 +++++++++++++++++++++++--
 2 files changed, 60 insertions(+), 5 deletions(-)

diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst
index d55c2a22ec7a..94c4680fdf3e 100644
--- a/Documentation/networking/netconsole.rst
+++ b/Documentation/networking/netconsole.rst
@@ -124,7 +124,7 @@ To remove a target::
 
 The interface exposes these parameters of a netconsole target to userspace:
 
-	==============  =================================       ============
+	=============== =================================       ============
 	enabled		Is this target currently enabled?	(read-write)
 	extended	Extended mode enabled			(read-write)
 	release		Prepend kernel release to message	(read-write)
@@ -135,7 +135,8 @@ The interface exposes these parameters of a netconsole target to userspace:
 	remote_ip	Remote agent's IP address		(read-write)
 	local_mac	Local interface's MAC address		(read-only)
 	remote_mac	Remote agent's MAC address		(read-write)
-	==============  =================================       ============
+	transmit_errors	Number of packet send errors		(read-only)
+	=============== =================================       ============
 
 The "enabled" attribute is also used to control whether the parameters of
 a target can be updated or not -- you can modify the parameters of only
diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 01cf33fa7503..fe6f29171a83 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -36,6 +36,7 @@
 #include <linux/inet.h>
 #include <linux/configfs.h>
 #include <linux/etherdevice.h>
+#include <linux/u64_stats_sync.h>
 #include <linux/utsname.h>
 #include <linux/rtnetlink.h>
 
@@ -90,6 +91,12 @@ static DEFINE_MUTEX(target_cleanup_list_lock);
  */
 static struct console netconsole_ext;
 
+struct netconsole_target_stats  {
+	u64_stats_t xmit_drop_count;
+	u64_stats_t enomem_count;
+	struct u64_stats_sync syncp;
+} __aligned(2 * sizeof(u64));
+
 /**
  * struct netconsole_target - Represents a configured netconsole target.
  * @list:	Links this target into the target_list.
@@ -97,6 +104,7 @@ static struct console netconsole_ext;
  * @userdata_group:	Links to the userdata configfs hierarchy
  * @userdata_complete:	Cached, formatted string of append
  * @userdata_length:	String length of userdata_complete
+ * @stats:	Packet send stats for the target. Used for debugging.
  * @enabled:	On / off knob to enable / disable target.
  *		Visible from userspace (read-write).
  *		We maintain a strict 1:1 correspondence between this and
@@ -124,6 +132,7 @@ struct netconsole_target {
 	char userdata_complete[MAX_USERDATA_ENTRY_LENGTH * MAX_USERDATA_ITEMS];
 	size_t			userdata_length;
 #endif
+	struct netconsole_target_stats stats;
 	bool			enabled;
 	bool			extended;
 	bool			release;
@@ -262,6 +271,7 @@ static void netconsole_process_cleanups_core(void)
  *				|	remote_ip
  *				|	local_mac
  *				|	remote_mac
+ *				|	transmit_errors
  *				|	userdata/
  *				|		<key>/
  *				|			value
@@ -371,6 +381,21 @@ static ssize_t remote_mac_show(struct config_item *item, char *buf)
 	return sysfs_emit(buf, "%pM\n", to_target(item)->np.remote_mac);
 }
 
+static ssize_t transmit_errors_show(struct config_item *item, char *buf)
+{
+	struct netconsole_target *nt = to_target(item);
+	u64 xmit_drop_count, enomem_count;
+	unsigned int start;
+
+	do {
+		start = u64_stats_fetch_begin(&nt->stats.syncp);
+		xmit_drop_count = u64_stats_read(&nt->stats.xmit_drop_count);
+		enomem_count = u64_stats_read(&nt->stats.enomem_count);
+	} while (u64_stats_fetch_retry(&nt->stats.syncp, start));
+
+	return sysfs_emit(buf, "%llu\n", xmit_drop_count + enomem_count);
+}
+
 /*
  * This one is special -- targets created through the configfs interface
  * are not enabled (and the corresponding netpoll activated) by default.
@@ -842,6 +867,7 @@ CONFIGFS_ATTR(, remote_ip);
 CONFIGFS_ATTR_RO(, local_mac);
 CONFIGFS_ATTR(, remote_mac);
 CONFIGFS_ATTR(, release);
+CONFIGFS_ATTR_RO(, transmit_errors);
 
 static struct configfs_attribute *netconsole_target_attrs[] = {
 	&attr_enabled,
@@ -854,6 +880,7 @@ static struct configfs_attribute *netconsole_target_attrs[] = {
 	&attr_remote_ip,
 	&attr_local_mac,
 	&attr_remote_mac,
+	&attr_transmit_errors,
 	NULL,
 };
 
@@ -1058,6 +1085,33 @@ static struct notifier_block netconsole_netdev_notifier = {
 	.notifier_call  = netconsole_netdev_event,
 };
 
+/**
+ * netpoll_send_udp_count_errs - Wrapper for netpoll_send_udp that counts errors
+ * @nt: target to send message to
+ * @msg: message to send
+ * @len: length of message
+ *
+ * Calls netpoll_send_udp and classifies the return value. If an error
+ * occurred it increments statistics in nt->stats accordingly.
+ * Only calls netpoll_send_udp if CONFIG_NETCONSOLE_DYNAMIC is disabled.
+ */
+static void netpoll_send_udp_count_errs(struct netconsole_target *nt, const char *msg, int len)
+{
+	int result = netpoll_send_udp(&nt->np, msg, len);
+
+	if (IS_ENABLED(CONFIG_NETCONSOLE_DYNAMIC)) {
+		if (result == NET_XMIT_DROP) {
+			u64_stats_update_begin(&nt->stats.syncp);
+			u64_stats_inc(&nt->stats.xmit_drop_count);
+			u64_stats_update_end(&nt->stats.syncp);
+		} else if (result == -ENOMEM) {
+			u64_stats_update_begin(&nt->stats.syncp);
+			u64_stats_inc(&nt->stats.enomem_count);
+			u64_stats_update_end(&nt->stats.syncp);
+		}
+	}
+}
+
 /**
  * send_ext_msg_udp - send extended log message to target
  * @nt: target to send message to
@@ -1106,7 +1160,7 @@ static void send_ext_msg_udp(struct netconsole_target *nt, const char *msg,
 					     "%s", userdata);
 
 		msg_ready = buf;
-		netpoll_send_udp(&nt->np, msg_ready, msg_len);
+		netpoll_send_udp_count_errs(nt, msg_ready, msg_len);
 		return;
 	}
 
@@ -1169,7 +1223,7 @@ static void send_ext_msg_udp(struct netconsole_target *nt, const char *msg,
 			this_offset += this_chunk;
 		}
 
-		netpoll_send_udp(&nt->np, buf, this_header + this_offset);
+		netpoll_send_udp_count_errs(nt, buf, this_header + this_offset);
 		offset += this_offset;
 	}
 }
@@ -1215,7 +1269,7 @@ static void write_msg(struct console *con, const char *msg, unsigned int len)
 			tmp = msg;
 			for (left = len; left;) {
 				frag = min(left, MAX_PRINT_CHUNK);
-				netpoll_send_udp(&nt->np, tmp, frag);
+				netpoll_send_udp_count_errs(nt, tmp, frag);
 				tmp += frag;
 				left -= frag;
 			}
-- 
2.43.5

Re: [PATCH net-next v3 2/2] netcons: Add udp send fail statistics to netconsole

[Breno Leitao]

Hello Maksym,

Thanks for the patch, it is looking good. A few nits:

On Thu, Sep 12, 2024 at 10:28:52AM -0700, Maksym Kutsevol wrote:
> +/**
> + * netpoll_send_udp_count_errs - Wrapper for netpoll_send_udp that counts errors
> + * @nt: target to send message to
> + * @msg: message to send
> + * @len: length of message
> + *
> + * Calls netpoll_send_udp and classifies the return value. If an error
> + * occurred it increments statistics in nt->stats accordingly.
> + * Only calls netpoll_send_udp if CONFIG_NETCONSOLE_DYNAMIC is disabled.
> + */
> +static void netpoll_send_udp_count_errs(struct netconsole_target *nt, const char *msg, int len)
> +{
> +	int result = netpoll_send_udp(&nt->np, msg, len);

Would you get a "variable defined but not used" type of eror if
CONFIG_NETCONSOLE_DYNAMIC is disabled?

> +
> +	if (IS_ENABLED(CONFIG_NETCONSOLE_DYNAMIC)) {
> +		if (result == NET_XMIT_DROP) {
> +			u64_stats_update_begin(&nt->stats.syncp);
> +			u64_stats_inc(&nt->stats.xmit_drop_count);
> +			u64_stats_update_end(&nt->stats.syncp);
> +		} else if (result == -ENOMEM) {
> +			u64_stats_update_begin(&nt->stats.syncp);
> +			u64_stats_inc(&nt->stats.enomem_count);
> +			u64_stats_update_end(&nt->stats.syncp);
> +		}
> +	}

Would this look better?

	if (IS_ENABLED(CONFIG_NETCONSOLE_DYNAMIC)) {
		u64_stats_update_begin(&nt->stats.syncp);

		if (result == NET_XMIT_DROP)
			u64_stats_inc(&nt->stats.xmit_drop_count);
		else if (result == -ENOMEM)
			u64_stats_inc(&nt->stats.enomem_count);
		else
			WARN_ONCE(true, "invalid result: %d\n", result)

		u64_stats_update_end(&nt->stats.syncp);
	}

Thanks
--breno

Re: [PATCH net-next v3 2/2] netcons: Add udp send fail statistics to netconsole

[Maksym Kutsevol]

Hey Breno,
Thanks for looking into this.

On Thu, Sep 12, 2024 at 1:49 PM Breno Leitao <leitao@debian.org> wrote:
>
> Hello Maksym,
>
> Thanks for the patch, it is looking good. A few nits:
>
> On Thu, Sep 12, 2024 at 10:28:52AM -0700, Maksym Kutsevol wrote:
> > +/**
> > + * netpoll_send_udp_count_errs - Wrapper for netpoll_send_udp that counts errors
> > + * @nt: target to send message to
> > + * @msg: message to send
> > + * @len: length of message
> > + *
> > + * Calls netpoll_send_udp and classifies the return value. If an error
> > + * occurred it increments statistics in nt->stats accordingly.
> > + * Only calls netpoll_send_udp if CONFIG_NETCONSOLE_DYNAMIC is disabled.
> > + */
> > +static void netpoll_send_udp_count_errs(struct netconsole_target *nt, const char *msg, int len)
> > +{
> > +     int result = netpoll_send_udp(&nt->np, msg, len);
>
> Would you get a "variable defined but not used" type of eror if
> CONFIG_NETCONSOLE_DYNAMIC is disabled?
>
Most probably yes, I'll check. If so, I'll add __maybe_unused in the
next iteration.

> > +
> > +     if (IS_ENABLED(CONFIG_NETCONSOLE_DYNAMIC)) {
> > +             if (result == NET_XMIT_DROP) {
> > +                     u64_stats_update_begin(&nt->stats.syncp);
> > +                     u64_stats_inc(&nt->stats.xmit_drop_count);
> > +                     u64_stats_update_end(&nt->stats.syncp);
> > +             } else if (result == -ENOMEM) {
> > +                     u64_stats_update_begin(&nt->stats.syncp);
> > +                     u64_stats_inc(&nt->stats.enomem_count);
> > +                     u64_stats_update_end(&nt->stats.syncp);
> > +             }
> > +     }
>
> Would this look better?
>
>         if (IS_ENABLED(CONFIG_NETCONSOLE_DYNAMIC)) {
>                 u64_stats_update_begin(&nt->stats.syncp);
>
>                 if (result == NET_XMIT_DROP)
>                         u64_stats_inc(&nt->stats.xmit_drop_count);
>                 else if (result == -ENOMEM)
>                         u64_stats_inc(&nt->stats.enomem_count);
>                 else
>                         WARN_ONCE(true, "invalid result: %d\n", result)
>
>                 u64_stats_update_end(&nt->stats.syncp);
>         }
>
1. It will warn on positive result
2. If the last `else` is removed, it attempts locking when the result
is positive, so I'd not do it this way.



> Thanks
> --breno

Re: [PATCH net-next v3 2/2] netcons: Add udp send fail statistics to netconsole

[Maksym Kutsevol]

On Thu, Sep 12, 2024 at 1:58 PM Maksym Kutsevol <max@kutsevol.com> wrote:
>
> Hey Breno,
> Thanks for looking into this.
>
> On Thu, Sep 12, 2024 at 1:49 PM Breno Leitao <leitao@debian.org> wrote:
> >
> > Hello Maksym,
> >
> > Thanks for the patch, it is looking good. A few nits:
> >
> > On Thu, Sep 12, 2024 at 10:28:52AM -0700, Maksym Kutsevol wrote:
> > > +/**
> > > + * netpoll_send_udp_count_errs - Wrapper for netpoll_send_udp that counts errors
> > > + * @nt: target to send message to
> > > + * @msg: message to send
> > > + * @len: length of message
> > > + *
> > > + * Calls netpoll_send_udp and classifies the return value. If an error
> > > + * occurred it increments statistics in nt->stats accordingly.
> > > + * Only calls netpoll_send_udp if CONFIG_NETCONSOLE_DYNAMIC is disabled.
> > > + */
> > > +static void netpoll_send_udp_count_errs(struct netconsole_target *nt, const char *msg, int len)
> > > +{
> > > +     int result = netpoll_send_udp(&nt->np, msg, len);
> >
> > Would you get a "variable defined but not used" type of eror if
> > CONFIG_NETCONSOLE_DYNAMIC is disabled?
> >
> Most probably yes, I'll check. If so, I'll add __maybe_unused in the
> next iteration.

No, there's no warning. As it's used and then optimized out by the compiler.

Re: [PATCH net-next v3 2/2] netcons: Add udp send fail statistics to netconsole

[Breno Leitao]

On Thu, Sep 12, 2024 at 01:58:12PM -0400, Maksym Kutsevol wrote:
> Hey Breno,
> Thanks for looking into this.
> 
> On Thu, Sep 12, 2024 at 1:49 PM Breno Leitao <leitao@debian.org> wrote:
> >
> > Hello Maksym,
> >
> > Thanks for the patch, it is looking good. A few nits:
> >
> > On Thu, Sep 12, 2024 at 10:28:52AM -0700, Maksym Kutsevol wrote:
> > > +/**
> > > + * netpoll_send_udp_count_errs - Wrapper for netpoll_send_udp that counts errors
> > > + * @nt: target to send message to
> > > + * @msg: message to send
> > > + * @len: length of message
> > > + *
> > > + * Calls netpoll_send_udp and classifies the return value. If an error
> > > + * occurred it increments statistics in nt->stats accordingly.
> > > + * Only calls netpoll_send_udp if CONFIG_NETCONSOLE_DYNAMIC is disabled.
> > > + */
> > > +static void netpoll_send_udp_count_errs(struct netconsole_target *nt, const char *msg, int len)
> > > +{
> > > +     int result = netpoll_send_udp(&nt->np, msg, len);
> >
> > Would you get a "variable defined but not used" type of eror if
> > CONFIG_NETCONSOLE_DYNAMIC is disabled?
> >
> Most probably yes, I'll check. If so, I'll add __maybe_unused in the
> next iteration.
> 
> > > +
> > > +     if (IS_ENABLED(CONFIG_NETCONSOLE_DYNAMIC)) {
> > > +             if (result == NET_XMIT_DROP) {
> > > +                     u64_stats_update_begin(&nt->stats.syncp);
> > > +                     u64_stats_inc(&nt->stats.xmit_drop_count);
> > > +                     u64_stats_update_end(&nt->stats.syncp);
> > > +             } else if (result == -ENOMEM) {
> > > +                     u64_stats_update_begin(&nt->stats.syncp);
> > > +                     u64_stats_inc(&nt->stats.enomem_count);
> > > +                     u64_stats_update_end(&nt->stats.syncp);
> > > +             }
> > > +     }
> >
> > Would this look better?
> >
> >         if (IS_ENABLED(CONFIG_NETCONSOLE_DYNAMIC)) {
> >                 u64_stats_update_begin(&nt->stats.syncp);
> >
> >                 if (result == NET_XMIT_DROP)
> >                         u64_stats_inc(&nt->stats.xmit_drop_count);
> >                 else if (result == -ENOMEM)
> >                         u64_stats_inc(&nt->stats.enomem_count);
> >                 else
> >                         WARN_ONCE(true, "invalid result: %d\n", result)
> >
> >                 u64_stats_update_end(&nt->stats.syncp);
> >         }
> >
> 1. It will warn on positive result
> 2. If the last `else` is removed, it attempts locking when the result
> is positive, so I'd not do it this way.

Correct. We could replace the WARN_ONCE(true, ..) by
WARN_ONCE(result,..), but this might look worse.

Let's keep the way you proposed.

Other than that, the patch looks good.

Thanks

Re: [PATCH net-next v3 1/2] netpoll: Make netpoll_send_udp return status instead of void

[Breno Leitao]

On Thu, Sep 12, 2024 at 10:28:51AM -0700, Maksym Kutsevol wrote:
> netpoll_send_udp can return if send was successful.
> It will allow client code to be aware of the send status.
> 
> Possible return values are the result of __netpoll_send_skb (cast to int)
> and -ENOMEM. This doesn't cover the case when TX was not successful
> instantaneously and was scheduled for later, __netpoll__send_skb returns
> success in that case.
> 
> Signed-off-by: Maksym Kutsevol <max@kutsevol.com>

Reviewed-by: Breno Leitao <leitao@debian.org>

Thanks for addressing it. Two things you might want to consider:

1) There are some warnings related to this patch.
 a) Not CCed maintainers
 b) WARNING: line length of 95 exceeds 80 columns

You can see them here:
https://patchwork.kernel.org/project/netdevbpf/patch/20240912173608.1821083-2-max@kutsevol.com/

Also, this might conflict with the refactor I did a while ago, so, you
might need to rebase:

https://lore.kernel.org/all/20240910100410.2690012-1-leitao@debian.org/

Other than that, I am happy with it.

Thanks for doing it
-breno