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SubjectRe: [PATCH 4/5] usb,early_printk: unregister early usb before rest_init()

* Jason Wessel <jason.wessel@windriver.com> wrote:

> The early_printk EHCI debug driver can hang the system or cause
> unpredictable results because two separate APIs will attempt to write
> to the mapped PCI region.
>
> The safe route is to unregister the early USB console at the end of
> the core kernel init, which is before the PCI initialization. Later,
> after the USB initialization completes it is then possible to register
> the console against the usb debug device and receive the printk
> messages that were missed in the period between early printk
> availability and the USB console device.
>
> Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
> ---
> arch/x86/kernel/early_printk.c | 22 ++++++++++++++++++++++
> 1 files changed, 22 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
> index e38c467..ef177d4 100644
> --- a/arch/x86/kernel/early_printk.c
> +++ b/arch/x86/kernel/early_printk.c
> @@ -952,4 +952,26 @@ static int __init setup_early_printk(char *buf)
> return 0;
> }
>
> +#ifdef CONFIG_EARLY_PRINTK_DBGP
> +/*
> + * The early console must get unregistered prior to the ECHI
> + * controller getting reset else the debug device cannot be used until
> + * a subsequent EHCI reset, or the kernel hangs.
> + */
> +static int __init usb_early_debug_cleanup(void)
> +{
> + if (early_dbgp_console.index >= 0 &&
> + early_dbgp_console.flags & CON_PRINTBUFFER) {
> + console_stop(early_console);
> + unregister_console(early_console);
> + early_dbgp_console.index = -1;
> + early_dbgp_console.flags = 0;
> + ehci_debug = NULL;
> + printk(KERN_INFO "Early USB console unregistered\n");
> + }
> + return 0;
> +}
> +postcore_initcall(usb_early_debug_cleanup);
> +#endif /* CONFIG_EARLY_PRINTK_DBGP */

We already have CON_BOOT which allows the unregistering of early
consoles, via disable_boot_consoles() initcall in kernel/printk.c.

The hang should be solved differently: either by calling
disable_boot_consoles() explicitly after console_init() - or by
introducing another CON_ flag that marks the console for early
forced unregistering.

Ingo


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