Re: [PATCH v10 3/3] x86/earlyprintk: setup earlyprintk as early as possible

[Borislav Petkov]

On Sun, Jun 07, 2015 at 08:14:37PM +0600, Alexander Kuleshov wrote:
> The early_printk function 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'. This patchset makes earlyprintk
> usable before the call of the 'parse_early_param'.
> 
> This patch makes the setup_early_printk visible for head{32,64}.c. So the
> 'early_printk' function will be usabable after decompression of the
> kernel and before parse_early_param will be called. It also must be
> safe if CONFIG_CMDLINE_BOOL and CONFIG_CMDLINE_OVERRIDE are set, because
> setup_cmdline function will be called before setup_early_printk.
> 
> It provides earlyprintk only for serial console, because other needs in
> ioremap which is not initialized yet.
> 
> Tested it with qemu, so early_printk() is usable and prints to serial
> console right after setup_early_printk function called.
> 
> Signed-off-by: Alexander Kuleshov <kuleshovmail@xxxxxxxxx>
> ---
>  arch/x86/include/asm/setup.h   |  7 +++++++
>  arch/x86/kernel/early_printk.c | 30 ++++++++++++++++++++++++++++--
>  arch/x86/kernel/head32.c       |  7 +++++++
>  arch/x86/kernel/head64.c       |  6 ++++++
>  4 files changed, 48 insertions(+), 2 deletions(-)

...

> diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
> index 92e8b5f..6969d97 100644
> --- a/arch/x86/kernel/head32.c
> +++ b/arch/x86/kernel/head32.c
> @@ -32,6 +32,13 @@ static void __init i386_default_early_setup(void)
>  asmlinkage __visible void __init i386_start_kernel(void)
>  {
>  	setup_builtin_cmdline();
> +
> +	lockdep_init();
> +
> +	setup_early_serial_console();
> +
> +	early_printk("Early printk 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..769d411 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -174,7 +174,12 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
>  
>  	setup_builtin_cmdline();
>  
> +	lockdep_init();

So you've added that lockdep_init() call here and above on the 32-bit
path and haven't removed the one in start_kernel().

* Then, your patches don't apply. Something garbles them insanely so that
not even fuzzy, ignore-context patch --merge works. Please fix your
setup. For that, send your patches to yourself and try applying them.
Send them out only if they apply cleanly.

And do them against tip/master or latest Linus rc, alternatively.

* To that patchset: I did the diff below ontop of yours to check whether
that early printk actually works.

And it doesn't on my test box here.

The beginning of my dmesg contains:

[    0.000000] bootconsole [earlyser0] enabled
[    0.000000] Initializing cgroup subsys cpuset
[    0.000000] Initializing cgroup subsys cpu
[    0.000000] Initializing cgroup subsys cpuacct
[    0.000000] Linux version 4.1.0-rc6+ (root@gondor) (gcc version 4.9.1 (Debian 4.9.1-19) ) #2 SMP PREEMPT Mon Jun 8 11:10:00 CEST 2015
[    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.1.0-rc6+ root=/dev/sda7 ro earlyprintk=ttyS0,115200 console=ttyS0,115200 console=tty0 root=/dev/sda7 log_buf_len=10M resume=/dev/sda5 no_console_suspend ignore_loglevel
[    0.000000] KERNEL supported cpus:
[    0.000000]   Intel GenuineIntel
[    0.000000]   AMD AuthenticAMD
[    0.000000]   Centaur CentaurHauls
[    0.000000] x86/fpu: xstate_offset[2]: 0240, xstate_sizes[2]: 0100
[    0.000000] x86/fpu: Supporting XSAVE feature 0x01: 'x87 floating point registers'
[    0.000000] x86/fpu: Supporting XSAVE feature 0x02: 'SSE registers'
[    0.000000] x86/fpu: Supporting XSAVE feature 0x04: 'AVX registers'
[    0.000000] x86/fpu: Enabled xstate features 0x7, context size is 0x340 bytes, using 'standard' format.
[    0.000000] x86/fpu: Using 'eager' FPU context switches.
[    0.000000] e820: BIOS-provided physical RAM map:
...

and I have CONFIG_EARLY_PRINTK=y. So provided I'm not missing anything,
I'd say you'd need to do more staring.

So I'd suggest you test your patches on bare metal, both 32-bit and
64-bit with a similar diff as the one I've done below.

HTH.

---
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index d4ea6ec28f09..20dd514ce838 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -179,7 +179,6 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 
 	early_printk("Early printk is initialized\n");
 
-
 	/*
 	 * Load microcode early on BSP.
 	 */
@@ -202,5 +201,7 @@ void __init x86_64_start_reservations(char *real_mode_data)
 
 	reserve_ebda_region();
 
+	early_printk("Will start_kernel\n");
+
 	start_kernel();
 }
diff --git a/init/main.c b/init/main.c
index 2115055faeac..e9180445283e 100644
--- a/init/main.c
+++ b/init/main.c
@@ -494,6 +494,8 @@ asmlinkage __visible void __init start_kernel(void)
 	char *command_line;
 	char *after_dashes;
 
+	early_printk("Will run lockdep_init needlessly one more time\n");
+
 	/*
 	 * Need to run as early as possible, to initialize the
 	 * lockdep hash:
@@ -530,6 +532,8 @@ asmlinkage __visible void __init start_kernel(void)
 	build_all_zonelists(NULL, NULL);
 	page_alloc_init();
 
+	early_printk("Early Kernel command line: %s\n", boot_command_line);
+
 	pr_notice("Kernel command line: %s\n", boot_command_line);
 	parse_early_param();
 	after_dashes = parse_args("Booting kernel",


-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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