linux-kernel - Re: [PATCH 4/5] kernfs: implement kernfs_path

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Message-ID: <20150709214143.GD18734@mtj.duckdns.org>
Date:	Thu, 9 Jul 2015 17:41:43 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Nikolay Borisov <n.borisov@...eground.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, axboe@...nel.dk,
	jack@...e.cz, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 4/5] kernfs: implement kernfs_path_len()

Hello, Nioklay.

I restored the cc list.  Please use reply-to-all.

On Wed, Jul 08, 2015 at 11:08:43AM +0300, Nikolay Borisov wrote:
> > +size_t kernfs_path_len(struct kernfs_node *kn)
> > +{
> > +	size_t len = 0;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&kernfs_rename_lock, flags);
> > +
> > +	do {
> > +		len += strlen(kn->name) + 1;
> > +		kn = kn->parent;
> > +	} while (kn && kn->parent);
> > +
> > +	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
> > +
> > +	return len;
> > +}
> > +
> 
> Can you explain the reason why you need to disable the irqs while
> executing this function? Presumably it has to do with the context of its
> usage - tracepoints but I wasn't able to find any information about the
> implications of interrupts being enabled while in a trace point?

It doesn't have much to do with the specific usage.
kernfs_rename_lock is irq-safe because we want to be able to call
functions like kernfs_name() and kernfs_path() regardless of the
current context.

Thanks.

-- 
tejun
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