printk: Add execution context (task name/CPU) to printk_info

Extend struct printk_info to include the task name, pid, and CPU
number where printk messages originate. This information is captured
at vprintk_store() time and propagated through printk_message to
nbcon_write_context, making it available to nbcon console drivers.

This is useful for consoles like netconsole that want to include
execution context in their output, allowing correlation of messages
with specific tasks and CPUs regardless of where the console driver
actually runs.

The feature is controlled by CONFIG_PRINTK_EXECUTION_CTX, which is
automatically selected by CONFIG_NETCONSOLE_DYNAMIC. When disabled,
the helper functions compile to no-ops with no overhead.

Suggested-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20260206-nbcon-v7-1-62bda69b1b41@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 53 insertions, 1 deletions

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 1d765ad242b8..cf6b52861036 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2131,11 +2131,39 @@ static inline void printk_delay(int level)
 	}
 }
 
+#define CALLER_ID_MASK 0x80000000
+
 static inline u32 printk_caller_id(void)
 {
 	return in_task() ? task_pid_nr(current) :
-		0x80000000 + smp_processor_id();
+		CALLER_ID_MASK + smp_processor_id();
+}
+
+#ifdef CONFIG_PRINTK_EXECUTION_CTX
+/* Store the opposite info than caller_id. */
+static u32 printk_caller_id2(void)
+{
+	return !in_task() ? task_pid_nr(current) :
+		CALLER_ID_MASK + smp_processor_id();
+}
+
+static pid_t printk_info_get_pid(const struct printk_info *info)
+{
+	u32 caller_id = info->caller_id;
+	u32 caller_id2 = info->caller_id2;
+
+	return caller_id & CALLER_ID_MASK ? caller_id2 : caller_id;
+}
+
+static int printk_info_get_cpu(const struct printk_info *info)
+{
+	u32 caller_id = info->caller_id;
+	u32 caller_id2 = info->caller_id2;
+
+	return ((caller_id & CALLER_ID_MASK ?
+		 caller_id : caller_id2) & ~CALLER_ID_MASK);
 }
+#endif
 
 /**
  * printk_parse_prefix - Parse level and control flags.
@@ -2213,6 +2241,28 @@ static u16 printk_sprint(char *text, u16 size, int facility,
 	return text_len;
 }
 
+#ifdef CONFIG_PRINTK_EXECUTION_CTX
+static void printk_store_execution_ctx(struct printk_info *info)
+{
+	info->caller_id2 = printk_caller_id2();
+	get_task_comm(info->comm, current);
+}
+
+static void pmsg_load_execution_ctx(struct printk_message *pmsg,
+				    const struct printk_info *info)
+{
+	pmsg->cpu = printk_info_get_cpu(info);
+	pmsg->pid = printk_info_get_pid(info);
+	memcpy(pmsg->comm, info->comm, sizeof(pmsg->comm));
+	static_assert(sizeof(pmsg->comm) == sizeof(info->comm));
+}
+#else
+static void printk_store_execution_ctx(struct printk_info *info) {}
+
+static void pmsg_load_execution_ctx(struct printk_message *pmsg,
+				    const struct printk_info *info) {}
+#endif
+
 __printf(4, 0)
 int vprintk_store(int facility, int level,
 		  const struct dev_printk_info *dev_info,
@@ -2320,6 +2370,7 @@ int vprintk_store(int facility, int level,
 	r.info->caller_id = caller_id;
 	if (dev_info)
 		memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
+	printk_store_execution_ctx(r.info);
 
 	/* A message without a trailing newline can be continued. */
 	if (!(flags & LOG_NEWLINE))
@@ -3002,6 +3053,7 @@ bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
 	pmsg->seq = r.info->seq;
 	pmsg->dropped = r.info->seq - seq;
 	force_con = r.info->flags & LOG_FORCE_CON;
+	pmsg_load_execution_ctx(pmsg, r.info);
 
 	/*
 	 * Skip records that are not forced to be printed on consoles and that