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

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Message-ID: <20091016125752.GB24518@elte.hu>
Date:	Fri, 16 Oct 2009 14:57:52 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Artem Bityutskiy <dedekind1@...il.com>
Cc:	Simon Kagstrom <simon.kagstrom@...insight.net>,
	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


* Artem Bityutskiy <dedekind1@...il.com> wrote:

> On Fri, 2009-10-16 at 12:10 +0200, Ingo Molnar wrote:
> > * 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);
> 
> And while we are on it, I think these extra lines before and after 
> spinlocks are unneeded and even a bit annoying :-)

To me they increase readability quite a bit as it allows me to 
concentrate on just the inner critical section without the distraction 
of the lock/unlock sequence. YMMV.

	Ingo
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