linux-kernel - Regression in 4.9-rc1 for PPC32 - bisected to commit 05fd007e4629

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Message-ID: <2ccf74f5-5fa2-2f47-ade1-69addc79c40b@lwfinger.net>
Date:   Thu, 20 Oct 2016 00:55:10 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     LKML <linux-kernel@...r.kernel.org>,
        Paul Burton <paul.burton@...tec.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thorsten Leemhuis <regressions@...mhuis.info>
Subject: Regression in 4.9-rc1 for PPC32 - bisected to commit 05fd007e4629

Kernel 4.9-rc1 fails to boot on my PowerBook G4 Aluminum (32-bit PowerPC) with 
the following splat:

Kernel Panic - not synching: Attempted to kill init: exitcode = 0x00000200

Call trace:

dump_stack+0x24/0x34 (unreliable)
panic+0x110/0x2ac
do_exit+0x464/0x834
do_group_exit+0x84/0xac
__wake_up_parent+0x0/0x34
ret_from_syscall+0x0/0x40

As the panic happens very early, I was not able to capture the output, thus the 
above was entered by hand.

The problem was bisected to commit 05fd007e4629 ("console: don't prefer first 
registered if DT specifies stdout-path"). Examining that patch and testing the 
various hunks, I found that the system booted fine when I eliminated the hunk at

--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -2077,6 +2077,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align))
                         name = of_get_property(of_aliases, "stdout", NULL);
                 if (name)
                         of_stdout = of_find_node_opts_by_path(name, 
&of_stdout_options);
+               if (of_stdout)
+                       console_set_by_of();
         }

         if (!of_aliases)

Similarly, it would boot if I eliminated the hunk at

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2647,7 +2658,7 @@ void register_console(struct console *newcon)
          *      didn't select a console we take the first one
          *      that registers here.
          */
-       if (preferred_console < 0) {
+       if (preferred_console < 0 && !of_specified_console) {
                 if (newcon->index < 0)
                         newcon->index = 0;
                 if (newcon->setup == NULL ||

The problem happens when of_specified_console is true, and the code following 
the modified if statement above is not executed. In my .config, CONFIG_OF=y.

As always, I will be happy to test any fixes.

Thanks,

Larry

-- 
If I was stranded on an island and the only way to get off
the island was to make a pretty UI, I’d die there.

Linus Torvalds