linux-kernel - Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability

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Date:   Wed, 9 Nov 2016 10:37:11 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, linux-usb@...r.kernel.org,
        x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug
 capability

On Tue, 1 Nov 2016, Lu Baolu wrote:
> +static void early_xdbc_write(struct console *con, const char *str, u32 n)
> +{
> +	int chunk, ret;
> +	static char buf[XDBC_MAX_PACKET];
> +	int use_cr = 0;
> +
> +	if (!xdbc.xdbc_reg)
> +		return;
> +	memset(buf, 0, XDBC_MAX_PACKET);

How is that dealing with reentrancy?

early_printk() does not protect against it. Peter has a patch to prevent
concurrent access from different cpus, but it cannot and will never prevent
reentrancy on the same cpu (interrupt, nmi).

Thanks,

	tglx