3 files changed, 92 insertions, 15 deletions

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 7199d60bfc25..f6161cd75d7d 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -13,6 +13,12 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
 #define printk_sysctl_init() do { } while (0)
 #endif
 
+#define con_printk(lvl, con, fmt, ...)				\
+	printk(lvl pr_fmt("%s%sconsole [%s%d] " fmt),		\
+		(con->flags & CON_NBCON) ? "" : "legacy ",	\
+		(con->flags & CON_BOOT) ? "boot" : "",		\
+		con->name, con->index, ##__VA_ARGS__)
+
 #ifdef CONFIG_PRINTK
 
 #ifdef CONFIG_PRINTK_CALLER
@@ -63,8 +69,9 @@ void defer_console_output(void);
 u16 printk_parse_prefix(const char *text, int *level,
 			enum printk_info_flags *flags);
 
+bool nbcon_alloc(struct console *con);
 void nbcon_init(struct console *con);
-void nbcon_cleanup(struct console *con);
+void nbcon_free(struct console *con);
 
 #else
 
@@ -81,8 +88,9 @@ void nbcon_cleanup(struct console *con);
 #define printk_safe_exit_irqrestore(flags) local_irq_restore(flags)
 
 static inline bool printk_percpu_data_ready(void) { return false; }
+static inline bool nbcon_alloc(struct console *con) { return false; }
 static inline void nbcon_init(struct console *con) { }
-static inline void nbcon_cleanup(struct console *con) { }
+static inline void nbcon_free(struct console *con) { }
 
 #endif /* CONFIG_PRINTK */
 
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index a2a354f859f9..ba1febf15db6 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -5,6 +5,7 @@
 #include <linux/kernel.h>
 #include <linux/console.h>
 #include <linux/delay.h>
+#include <linux/slab.h>
 #include "internal.h"
 /*
  * Printk console printing implementation for consoles which does not depend
@@ -70,6 +71,10 @@
  *      console is an unsafe state. It is used only in panic() by the final
  *      attempt to flush consoles in a try and hope mode.
  *
+ *      Note that separate record buffers are used in panic(). As a result,
+ *      the messages can be read and formatted without any risk even after
+ *      using the hostile takeover in unsafe state.
+ *
  * The release function simply clears the 'prio' field.
  *
  * All operations on @console::nbcon_state are atomic cmpxchg based to
@@ -459,6 +464,8 @@ static int nbcon_context_try_acquire_hostile(struct nbcon_context *ctxt,
 	return 0;
 }
 
+static struct printk_buffers panic_nbcon_pbufs;
+
 /**
  * nbcon_context_try_acquire - Try to acquire nbcon console
  * @ctxt:	The context of the caller
@@ -473,6 +480,7 @@ static int nbcon_context_try_acquire_hostile(struct nbcon_context *ctxt,
 __maybe_unused
 static bool nbcon_context_try_acquire(struct nbcon_context *ctxt)
 {
+	unsigned int cpu = smp_processor_id();
 	struct console *con = ctxt->console;
 	struct nbcon_state cur;
 	int err;
@@ -491,7 +499,18 @@ try_again:
 
 	err = nbcon_context_try_acquire_hostile(ctxt, &cur);
 out:
-	return !err;
+	if (err)
+		return false;
+
+	/* Acquire succeeded. */
+
+	/* Assign the appropriate buffer for this context. */
+	if (atomic_read(&panic_cpu) == cpu)
+		ctxt->pbufs = &panic_nbcon_pbufs;
+	else
+		ctxt->pbufs = con->pbufs;
+
+	return true;
 }
 
 static bool nbcon_owner_matches(struct nbcon_state *cur, int expected_cpu,
@@ -530,7 +549,7 @@ static void nbcon_context_release(struct nbcon_context *ctxt)
 
 	do {
 		if (!nbcon_owner_matches(&cur, cpu, ctxt->prio))
-			return;
+			break;
 
 		new.atom = cur.atom;
 		new.prio = NBCON_PRIO_NONE;
@@ -542,26 +561,70 @@ static void nbcon_context_release(struct nbcon_context *ctxt)
 		new.unsafe |= cur.unsafe_takeover;
 
 	} while (!nbcon_state_try_cmpxchg(con, &cur, &new));
+
+	ctxt->pbufs = NULL;
+}
+
+/**
+ * nbcon_alloc - Allocate buffers needed by the nbcon console
+ * @con:	Console to allocate buffers for
+ *
+ * Return:	True on success. False otherwise and the console cannot
+ *		be used.
+ *
+ * This is not part of nbcon_init() because buffer allocation must
+ * be performed earlier in the console registration process.
+ */
+bool nbcon_alloc(struct console *con)
+{
+	if (con->flags & CON_BOOT) {
+		/*
+		 * Boot console printing is synchronized with legacy console
+		 * printing, so boot consoles can share the same global printk
+		 * buffers.
+		 */
+		con->pbufs = &printk_shared_pbufs;
+	} else {
+		con->pbufs = kmalloc(sizeof(*con->pbufs), GFP_KERNEL);
+		if (!con->pbufs) {
+			con_printk(KERN_ERR, con, "failed to allocate printing buffer\n");
+			return false;
+		}
+	}
+
+	return true;
 }
 
 /**
  * nbcon_init - Initialize the nbcon console specific data
  * @con:	Console to initialize
+ *
+ * nbcon_alloc() *must* be called and succeed before this function
+ * is called.
  */
 void nbcon_init(struct console *con)
 {
 	struct nbcon_state state = { };
 
+	/* nbcon_alloc() must have been called and successful! */
+	BUG_ON(!con->pbufs);
+
 	nbcon_state_set(con, &state);
 }
 
 /**
- * nbcon_cleanup - Cleanup the nbcon console specific data
- * @con:	Console to cleanup
+ * nbcon_free - Free and cleanup the nbcon console specific data
+ * @con:	Console to free/cleanup nbcon data
  */
-void nbcon_cleanup(struct console *con)
+void nbcon_free(struct console *con)
 {
 	struct nbcon_state state = { };
 
 	nbcon_state_set(con, &state);
+
+	/* Boot consoles share global printk buffers. */
+	if (!(con->flags & CON_BOOT))
+		kfree(con->pbufs);
+
+	con->pbufs = NULL;
 }
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 17def3791bc0..1c9720acd960 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3331,12 +3331,6 @@ static void try_enable_default_console(struct console *newcon)
 		newcon->flags |= CON_CONSDEV;
 }
 
-#define con_printk(lvl, con, fmt, ...)				\
-	printk(lvl pr_fmt("%s%sconsole [%s%d] " fmt),		\
-	       (con->flags & CON_NBCON) ? "" : "legacy ",	\
-	       (con->flags & CON_BOOT) ? "boot" : "",		\
-	       con->name, con->index, ##__VA_ARGS__)
-
 static void console_init_seq(struct console *newcon, bool bootcon_registered)
 {
 	struct console *con;
@@ -3450,6 +3444,15 @@ void register_console(struct console *newcon)
 		goto unlock;
 	}
 
+	if (newcon->flags & CON_NBCON) {
+		/*
+		 * Ensure the nbcon console buffers can be allocated
+		 * before modifying any global data.
+		 */
+		if (!nbcon_alloc(newcon))
+			goto unlock;
+	}
+
 	/*
 	 * See if we want to enable this console driver by default.
 	 *
@@ -3477,8 +3480,11 @@ void register_console(struct console *newcon)
 		err = try_enable_preferred_console(newcon, false);
 
 	/* printk() messages are not printed to the Braille console. */
-	if (err || newcon->flags & CON_BRL)
+	if (err || newcon->flags & CON_BRL) {
+		if (newcon->flags & CON_NBCON)
+			nbcon_free(newcon);
 		goto unlock;
+	}
 
 	/*
 	 * If we have a bootconsole, and are switching to a real console,
@@ -3589,7 +3595,7 @@ static int unregister_console_locked(struct console *console)
 	synchronize_srcu(&console_srcu);
 
 	if (console->flags & CON_NBCON)
-		nbcon_cleanup(console);
+		nbcon_free(console);
 
 	console_sysfs_notify();