Re: [PATCH v5 14/16] printk: Do not set Braille console as preferred_console

[Chris Down <chris@chrisdown.name>]

Petr Mladek writes:
>-	if (brl_options)
>+	if (is_new_entry)
>+		INIT_LIST_HEAD(&pc->preferred_dev_node);

is_new_entry is derived from pc->name[0]/pc->devname[0] being empty, and
console_setup() can store an empty name:

    console=,115200 console=tty1

The first one creates an entry with name "" (and links it). The second one 
stops the lookup loop at the same slot, sees it as new again, and 
re-initialises a node which is still linked, followed by list_add(). With 
DEBUG_LIST + BUG_ON_DATA_CORRUPTION:

    list_add corruption. next->prev should be prev (ffffb010209fc0c0), but was ffffb01023cd1fa0. (next=ffffb01023cd1fa0).
    kernel BUG at lib/list_debug.c:29!
    Call trace:
     __list_add_valid_or_report+0xbc/0x1c0 (P)
     add_or_update_preferred_console+0x6fc/0x9c0
     __add_preferred_console+0x11c/0x160
     console_setup+0x2e4/0x348
     obsolete_checksetup+0x148/0x190
     unknown_bootoption+0x150/0x328
     parse_one+0x108/0x480
     parse_args+0x158/0x3d0
     start_kernel+0x134/0x488

"console=,foo:bar" does the same on the first console= when SPCR added an 
entry, since it matches the SPCR slot via the empty devname (see 7/16).

Rejecting empty name/devname in add_or_update_preferred_console() (see my 
comment on 7/16) should fix that.

>-		preferred_dev_console = i;
>+		if (!list_empty(&pc->preferred_dev_node))
>+			list_del_init(&pc->preferred_dev_node);
>+	} else if (!is_braille_console_preferred(pc)) {
>+		if (list_empty(&pc->preferred_dev_node))
>+			list_add(&pc->preferred_dev_node, &preferred_dev_console);
>+		else
>+			list_move(&pc->preferred_dev_node, &preferred_dev_console);

list_del_init() and list_move() are both fine on an initialised self-linked 
node (list_move() passes the DEBUG_LIST checks in __list_del_entry_valid()), so 
the list_empty() checks can go.

With these fixed:

Acked-by: Chris Down <chris@chrisdown.name>

Thanks!