linux-kernel - Re: [PATCH v10 4/5] core: Add kernel message dumper to call on oopses and panics

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Date:	Fri, 16 Oct 2009 12:10:45 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Simon Kagstrom <simon.kagstrom@...insight.net>
Cc:	dedekind1@...il.com, linux-mtd <linux-mtd@...ts.infradead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Koskinen Aaro (Nokia-D/Helsinki)" <aaro.koskinen@...ia.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH v10 4/5] core: Add kernel message dumper to call on
	oopses and panics


* Simon Kagstrom <simon.kagstrom@...insight.net> wrote:

> +int kmsg_dump_register(struct kmsg_dumper *dumper)
> +{
> +	unsigned long flags;
> +
> +	/* The dump callback needs to be set */
> +	if (!dumper->dump)
> +		return -EINVAL;
> +
> +	spin_lock_irqsave(&dump_list_lock, flags);
> +
> +	/* Don't allow registering multiple times */
> +	if (dumper->registered) {
> +		spin_unlock_irqrestore(&dump_list_lock, flags);
> +
> +		return -EBUSY;
> +	}
> +
> +	dumper->registered = 1;
> +	list_add(&dumper->list, &dump_list);
> +	spin_unlock_irqrestore(&dump_list_lock, flags);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(kmsg_dump_register);


i dont want to bikeshed paint this but this sequence caught my eyes. We 
generally do flatter and clearer locking sequences:

int kmsg_dump_register(struct kmsg_dumper *dumper)
{
	unsigned long flags;
	int err = -EBUSY;

	/* The dump callback needs to be set */
	if (!dumper->dump)
		return -EINVAL;

	spin_lock_irqsave(&dump_list_lock, flags);

	/* Don't allow registering multiple times */
	if (!dumper->registered) {
		dumper->registered = 1;
		list_add_tail(&dumper->list, &dump_list);
		err = 0;
	}

	spin_unlock_irqrestore(&dump_list_lock, flags);

	return err;
}
EXPORT_SYMBOL_GPL(kmsg_dump_register);

(warning: untested, written in mail editor)

Same goes for kmsg_dump_unregister().

	Ingo
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