Merge tag 'printk-for-6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk updates from Petr Mladek:

 - Add NMI-safe SRCU reader API. It uses atomic_inc() instead of
   this_cpu_inc() on strong load-store architectures.

 - Introduce new console_list_lock to synchronize a manipulation of the
   list of registered consoles and their flags.

   This is a first step in removing the big-kernel-lock-like behavior of
   console_lock(). This semaphore still serializes console->write()
   calbacks against:

      - each other. It primary prevents potential races between early
        and proper console drivers using the same device.

      - suspend()/resume() callbacks and init() operations in some
        drivers.

      - various other operations in the tty/vt and framebufer
        susbsystems. It is likely that console_lock() serializes even
        operations that are not directly conflicting with the
        console->write() callbacks here. This is the most complicated
        big-kernel-lock aspect of the console_lock() that will be hard
        to untangle.

 - Introduce new console_srcu lock that is used to safely iterate and
   access the registered console drivers under SRCU read lock.

   This is a prerequisite for introducing atomic console drivers and
   console kthreads. It will reduce the complexity of serialization
   against normal consoles and console_lock(). Also it should remove the
   risk of deadlock during critical situations, like Oops or panic, when
   only atomic consoles are registered.

 - Check whether the console is registered instead of enabled on many
   locations. It was a historical leftover.

 - Cleanly force a preferred console in xenfb code instead of a dirty
   hack.

 - A lot of code and comment clean ups and improvements.

* tag 'printk-for-6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: (47 commits)
  printk: htmldocs: add missing description
  tty: serial: sh-sci: use setup() callback for early console
  printk: relieve console_lock of list synchronization duties
  tty: serial: kgdboc: use console_list_lock to trap exit
  tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console()
  tty: serial: kgdboc: use console_list_lock for list traversal
  tty: serial: kgdboc: use srcu console list iterator
  proc: consoles: use console_list_lock for list iteration
  tty: tty_io: use console_list_lock for list synchronization
  printk, xen: fbfront: create/use safe function for forcing preferred
  netconsole: avoid CON_ENABLED misuse to track registration
  usb: early: xhci-dbc: use console_is_registered()
  tty: serial: xilinx_uartps: use console_is_registered()
  tty: serial: samsung_tty: use console_is_registered()
  tty: serial: pic32_uart: use console_is_registered()
  tty: serial: earlycon: use console_is_registered()
  tty: hvc: use console_is_registered()
  efi: earlycon: use console_is_registered()
  tty: nfcon: use console_is_registered()
  serial_core: replace uart_console_enabled() with uart_console_registered()
  ...

1 files changed, 16 insertions, 4 deletions

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index 62f773286d44..76452fe2af86 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -3054,15 +3054,29 @@ static struct console serial_console = {
 };
 
 #ifdef CONFIG_SUPERH
+static char early_serial_buf[32];
+
+static int early_serial_console_setup(struct console *co, char *options)
+{
+	/*
+	 * This early console is always registered using the earlyprintk=
+	 * parameter, which does not call add_preferred_console(). Thus
+	 * @options is always NULL and the options for this early console
+	 * are passed using a custom buffer.
+	 */
+	WARN_ON(options);
+
+	return serial_console_setup(co, early_serial_buf);
+}
+
 static struct console early_serial_console = {
 	.name           = "early_ttySC",
 	.write          = serial_console_write,
+	.setup		= early_serial_console_setup,
 	.flags          = CON_PRINTBUFFER,
 	.index		= -1,
 };
 
-static char early_serial_buf[32];
-
 static int sci_probe_earlyprintk(struct platform_device *pdev)
 {
 	const struct plat_sci_port *cfg = dev_get_platdata(&pdev->dev);
@@ -3074,8 +3088,6 @@ static int sci_probe_earlyprintk(struct platform_device *pdev)
 
 	sci_init_single(pdev, &sci_ports[pdev->id], pdev->id, cfg, true);
 
-	serial_console_setup(&early_serial_console, early_serial_buf);
-
 	if (!strstr(early_serial_buf, "keep"))
 		early_serial_console.flags |= CON_BOOT;