[PATCH v14 3/4] x86/earlyprintk: setup earlyprintk as early as possible

[Alexander Kuleshov]

The earlyprintk is usable only after the setup_early_printk() will
be executed. We pass 'earlyprintk' through the kernel command line, so it
will be usable only after the parse_early_param() will be executed. This means
that we have usable earlyprintk only during early boot, kernel decompression
and after call of the parse_early_param(), but sometimes it is very useful to
know what occurs in between. The earlyprintk can allow us to know what occurs
after kernel decompression and before parse_early_param() will be called.
There are many stuff after the kernel decompression and before the
parse_early_param() will be called as memblock usage, early cpu initialization,
early ioremap initialization and etc... So earlyprintk allows us to see
what's going on there.

This patch provides the following stuff:

1. This patch introduces the setup_earlyprintk_console() function,
which called arch/x86/kernel/head{32,64}.c, parses kernel command line,
tries to find 'earlyprintk' option and calls setup_early_printk() depending
on the result.

2. As setup_earlyprintk_console() setups earlyprintk very early, we can't
use all console devices for now, but only serial and vga. There is
is_earlyprintk_late variable which determines ability to setup earlyprintk
for the certain device.

3. Call of the lockdep_init() added to the arch/x86/kernel/head{32,64}.c
to prevent call of the register_console before the initialization of lockdep.

In other way there we will get:

[ 0.000000] WARNING: lockdep init error! lock-(console_sem).lock was acquiredbefore lockdep_init
[ 0.000000] Call stack leading to lockdep invocation was:
[ 0.000000] [] save_stack_trace+0x2f/0x50
[ 0.000000] [] __lock_acquire+0xa2c/0xf00
[ 0.000000] [] lock_acquire+0xdb/0x2b0
[ 0.000000] [] _raw_spin_lock_irqsave+0x53/0x90
[ 0.000000] [] down+0x16/0x50
[ 0.000000] [] console_lock+0x19/0x60
[ 0.000000] [] register_console+0x116/0x350
[ 0.000000] [] setup_early_printk+0x165/0x467
[ 0.000000] [] setup_early_serial_console+0x56/0x58
[ 0.000000] [] x86_64_start_kernel+0xce/0x110
[ 0.000000] [] 0xffffffffffffffff
[ 0.000000] ------------------------

This patch adds lockdep_init() to the arch/x86/kernel/head{32,64}.c, but
not removed it from the init/main.c, because there is a couple of architectures
which have support of the lockdep, but do not call lockdep_init() in their
architecture-dependent code.

4. As setup_earlyprintk_console can be called twice: from
setup_earlyprintk_console() and parse_early_param(), additional check is added
to the really early consoles to prevent initialization of already initialized
consoles.

Tested with qemu, so early_printk() is usable and prints to serial
console right after setup_early_printk() function called.

We will not see earlyprintk messages in the dmesg buffer, because
it is too early to initialized log_buf.

Signed-off-by: Alexander Kuleshov <kuleshovmail@xxxxxxxxx>
---
 arch/x86/include/asm/setup.h   |  6 ++++++
 arch/x86/kernel/early_printk.c | 42 +++++++++++++++++++++++++++++++++++-------
 arch/x86/kernel/head32.c       |  4 ++++
 arch/x86/kernel/head64.c       |  5 +++++
 4 files changed, 50 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index 68d8c05..44f7059 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -127,0 +127,0 @@ asmlinkage void __init x86_64_start_reservations(char *real_mode_data);

 #endif /* __i386__ */
 void __init setup_builtin_cmdline(void);
+#ifdef CONFIG_EARLY_PRINTK
+/* used by arch/x86/kernel/head{32,64}.c */
+extern int __init setup_earlyprintk_console(void);
+#else
+static inline int __init setup_earlyprintk_console(void) { return 0; }
+#endif /* CONFIG_EARLY_PRINTK */
 #endif /* _SETUP */
 #else
 #define RESERVE_BRK(name,sz)				\
diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index 89427d8..10d4d82 100644
--- a/arch/x86/kernel/early_printk.c
+++ b/arch/x86/kernel/early_printk.c
@@ -329,6 +329,14 @@ static inline void early_console_register(struct console *con, int keep_early)
 	register_console(early_console);
 }
 
+/*
+ * The setup_early_printk can be called from two places: from the
+ * setup_earlyprintk_console() and the parse_early_param(). In the
+ * first case it is too early to setup earlyprintk for some devices
+ * as efi, pciserial and etc., but it can be set for vga and serial.
+ */
+static bool is_earlyprintk_late = true;
+
 static int __init setup_early_printk(char *buf)
 {
 	int keep;
@@ -342,47 +350,67 @@ static int __init setup_early_printk(char *buf)
 	keep = (strstr(buf, "keep") != NULL);
 
 	while (*buf != '\0') {
-		if (!strncmp(buf, "serial", 6)) {
+		if (!strncmp(buf, "serial", 6) &&
+		    early_serial_console.index == -1) {
 			buf += 6;
 			early_serial_init(buf);
 			early_console_register(&early_serial_console, keep);
 			if (!strncmp(buf, ",ttyS", 5))
 				buf += 5;
 		}
-		if (!strncmp(buf, "ttyS", 4)) {
+		if (!strncmp(buf, "ttyS", 4) &&
+		    early_serial_console.index == -1) {
 			early_serial_init(buf + 4);
 			early_console_register(&early_serial_console, keep);
 		}
 #ifdef CONFIG_PCI
-		if (!strncmp(buf, "pciserial", 9)) {
+		if (!strncmp(buf, "pciserial", 9) && is_earlyprintk_late) {
 			early_pci_serial_init(buf + 9);
 			early_console_register(&early_serial_console, keep);
 			buf += 9; /* Keep from match the above "serial" */
 		}
 #endif
 		if (!strncmp(buf, "vga", 3) &&
-		    boot_params.screen_info.orig_video_isVGA == 1) {
+		    boot_params.screen_info.orig_video_isVGA == 1 &&
+		    early_vga_console.index == -1) {
 			max_xpos = boot_params.screen_info.orig_video_cols;
 			max_ypos = boot_params.screen_info.orig_video_lines;
 			current_ypos = boot_params.screen_info.orig_y;
 			early_console_register(&early_vga_console, keep);
 		}
 #ifdef CONFIG_EARLY_PRINTK_DBGP
-		if (!strncmp(buf, "dbgp", 4) && !early_dbgp_init(buf + 4))
+		if (!strncmp(buf, "dbgp", 4) && !early_dbgp_init(buf + 4) &&
+		    is_earlyprintk_late)
 			early_console_register(&early_dbgp_console, keep);
 #endif
 #ifdef CONFIG_HVC_XEN
-		if (!strncmp(buf, "xen", 3))
+		if (!strncmp(buf, "xen", 3) && is_earlyprintk_late)
 			early_console_register(&xenboot_console, keep);
 #endif
 #ifdef CONFIG_EARLY_PRINTK_EFI
-		if (!strncmp(buf, "efi", 3))
+		if (!strncmp(buf, "efi", 3) && is_earlyprintk_late)
 			early_console_register(&early_efi_console, keep);
 #endif
 
 		buf++;
 	}
+
+	is_earlyprintk_late = true;
+
 	return 0;
 }
 
 early_param("earlyprintk", setup_early_printk);
+
+int __init setup_earlyprintk_console(void)
+{
+	char *arg;
+
+	arg = strstr(boot_command_line, "earlyprintk=");
+	if (!arg)
+		return -1;
+
+	is_earlyprintk_late = false;
+
+	return setup_early_printk(arg);
+}
diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
index 92e8b5f..64554be 100644
--- a/arch/x86/kernel/head32.c
+++ b/arch/x86/kernel/head32.c
@@ -32,2 +32,2 @@ static void __init i386_default_early_setup(void)
 asmlinkage __visible void __init i386_start_kernel(void)
 {
	setup_builtin_cmdline();
+	lockdep_init();
+	setup_earlyprintk_console();
+	early_printk("earlyprintk is initialized\n");
+
 	cr4_init_shadow();
 	sanitize_boot_params(&boot_params);
 
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 1e5f064..e61e5a8 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -174,0 +174,0 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)

 	setup_builtin_cmdline();
 
+	lockdep_init();
+	setup_earlyprintk_console();
+	early_printk("earlyprintk is initialized\n");
+
 	/*
 	 * Load microcode early on BSP.
 	 */
-- 
2.4.0.GIT

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