Re: [PATCH v5 07/16] printk: Ensure consistent name and devname when updating preferred console

[Chris Down <chris@chrisdown.name>]

Petr Mladek writes:
>-		strscpy(pc->name, name);
>-		pc->index = idx;
>+		if (!pc->name[0]) {
>+			is_new_entry = true;
>+			strscpy(pc->name, name);
>+			pc->index = idx;

console_setup() can hand us an empty name or devname:

    console=,115200   -> name "", idx 0, options "115200"
    console=,foo:bar  -> devname "", idx -1, options "foo:bar"

For the devname case, __add_preferred_console() matches the first name-only 
entry (`strcmp(pc->devname, "") == 0`), e.g. the SPCR "pl011"/0 entry, and this 
hunk now treats it as new.

Then index becomes -1 and options become "foo:bar", so the SPCR console never 
matches again. Before the series that command line only moved 
preferred_console.

For the `!pc->name[0]` branch below the slot keeps looking unused, which turns 
into list corruption with 14/16 (I'll put some details over there instead of 
duplicating it here).

Rejecting empty strings up front, after the `WARN_ON(!name && !devname)`, fixes 
both:

    	if ((name && !name[0]) || (devname && !devname[0])) {
    		pr_err("Adding a preferred console with an empty name\n");
    		return -EINVAL;
    	}