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Message-Id: <20260120-nbcon-v2-3-b61f960587a8@debian.org>
Date: Tue, 20 Jan 2026 08:23:49 -0800
From: Breno Leitao <leitao@...ian.org>
To: Breno Leitao <leitao@...ian.org>, Andrew Lunn <andrew+netdev@...n.ch>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
pmladek@...e.com, john.ogness@...utronix.de
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Steven Rostedt <rostedt@...dmis.org>,
Sergey Senozhatsky <senozhatsky@...omium.org>,
Andrew Morton <akpm@...ux-foundation.org>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, asantostc@...il.com, efault@....de,
gustavold@...il.com, calvin@...nvd.org, jv@...sburgh.net,
mpdesouza@...e.com, kernel-team@...a.com
Subject: [PATCH net-next v2 3/5] netconsole: convert to NBCON console
infrastructure
Convert netconsole from the legacy console API to the NBCON framework.
NBCON provides threaded printing which unblocks printk()s and flushes in
a thread, decoupling network TX from printk() when netconsole is
in use.
Since netconsole relies on the network stack which cannot safely operate
from all atomic contexts, mark both consoles with
CON_NBCON_ATOMIC_UNSAFE. (See discussion in [1])
CON_NBCON_ATOMIC_UNSAFE restricts write_atomic() usage to emergency
scenarios (panic) where regular messages are sent in threaded mode.
Implementation changes:
- Unify write_ext_msg() and write_msg() into netconsole_write()
- Add device_lock/device_unlock callbacks to manage target_list_lock
- Use nbcon_enter_unsafe()/nbcon_exit_unsafe() around network
operations.
- If nbcon_enter_unsafe() fails, just return given netconsole lost
the ownership of the console.
- Set write_thread and write_atomic callbacks (both use same function)
Link: https://lore.kernel.org/all/b2qps3uywhmjaym4mht2wpxul4yqtuuayeoq4iv4k3zf5wdgh3@tocu6c7mj4lt/ [1]
Signed-off-by: Breno Leitao <leitao@...ian.org>
---
drivers/net/netconsole.c | 97 ++++++++++++++++++++++++++++++------------------
1 file changed, 60 insertions(+), 37 deletions(-)
diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index dc3bd7c9b0498..c5d7e97fe2a78 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -1709,22 +1709,6 @@ static void send_ext_msg_udp(struct netconsole_target *nt, const char *msg,
sysdata_len);
}
-static void write_ext_msg(struct console *con, const char *msg,
- unsigned int len)
-{
- struct netconsole_target *nt;
- unsigned long flags;
-
- if ((oops_only && !oops_in_progress) || list_empty(&target_list))
- return;
-
- spin_lock_irqsave(&target_list_lock, flags);
- list_for_each_entry(nt, &target_list, list)
- if (nt->extended && nt->enabled && netif_running(nt->np.dev))
- send_ext_msg_udp(nt, msg, len);
- spin_unlock_irqrestore(&target_list_lock, flags);
-}
-
static void send_msg_udp(struct netconsole_target *nt, const char *msg,
unsigned int len)
{
@@ -1739,29 +1723,62 @@ static void send_msg_udp(struct netconsole_target *nt, const char *msg,
}
}
-static void write_msg(struct console *con, const char *msg, unsigned int len)
+/**
+ * netconsole_write - Generic function to send a msg to all targets
+ * @wctxt: nbcon write context
+ * @extended: "true" for extended console mode
+ *
+ * Given an nbcon write context, send the message to the netconsole targets
+ */
+static void netconsole_write(struct nbcon_write_context *wctxt, bool extended)
{
- unsigned long flags;
struct netconsole_target *nt;
if (oops_only && !oops_in_progress)
return;
- /* Avoid taking lock and disabling interrupts unnecessarily */
- if (list_empty(&target_list))
- return;
- spin_lock_irqsave(&target_list_lock, flags);
list_for_each_entry(nt, &target_list, list) {
- if (!nt->extended && nt->enabled && netif_running(nt->np.dev)) {
- /*
- * We nest this inside the for-each-target loop above
- * so that we're able to get as much logging out to
- * at least one target if we die inside here, instead
- * of unnecessarily keeping all targets in lock-step.
- */
- send_msg_udp(nt, msg, len);
- }
+ if (nt->extended != extended || !nt->enabled ||
+ !netif_running(nt->np.dev))
+ continue;
+
+ /* If nbcon_enter_unsafe() fails, just return given netconsole
+ * lost the ownership, and iterating over the targets will not
+ * be able to re-acquire.
+ */
+ if (!nbcon_enter_unsafe(wctxt))
+ return;
+
+ if (extended)
+ send_ext_msg_udp(nt, wctxt->outbuf, wctxt->len);
+ else
+ send_msg_udp(nt, wctxt->outbuf, wctxt->len);
+
+ nbcon_exit_unsafe(wctxt);
}
+}
+
+static void netconsole_write_ext(struct console *con __always_unused,
+ struct nbcon_write_context *wctxt)
+{
+ netconsole_write(wctxt, true);
+}
+
+static void netconsole_write_basic(struct console *con __always_unused,
+ struct nbcon_write_context *wctxt)
+{
+ netconsole_write(wctxt, false);
+}
+
+static void netconsole_device_lock(struct console *con __always_unused,
+ unsigned long *flags)
+{
+ spin_lock_irqsave(&target_list_lock, *flags);
+}
+
+static void netconsole_device_unlock(struct console *con __always_unused,
+ unsigned long flags)
+{
spin_unlock_irqrestore(&target_list_lock, flags);
}
@@ -1924,15 +1941,21 @@ static void free_param_target(struct netconsole_target *nt)
}
static struct console netconsole_ext = {
- .name = "netcon_ext",
- .flags = CON_ENABLED | CON_EXTENDED,
- .write = write_ext_msg,
+ .name = "netcon_ext",
+ .flags = CON_ENABLED | CON_EXTENDED | CON_NBCON | CON_NBCON_ATOMIC_UNSAFE,
+ .write_thread = netconsole_write_ext,
+ .write_atomic = netconsole_write_ext,
+ .device_lock = netconsole_device_lock,
+ .device_unlock = netconsole_device_unlock,
};
static struct console netconsole = {
- .name = "netcon",
- .flags = CON_ENABLED,
- .write = write_msg,
+ .name = "netcon",
+ .flags = CON_ENABLED | CON_NBCON | CON_NBCON_ATOMIC_UNSAFE,
+ .write_thread = netconsole_write_basic,
+ .write_atomic = netconsole_write_basic,
+ .device_lock = netconsole_device_lock,
+ .device_unlock = netconsole_device_unlock,
};
static int __init init_netconsole(void)
--
2.47.3
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