linux-kernel - Re: [PATCH 3.12-rc7] KVM: Fix modprobe failure for kvm_intel/kvm

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Message-ID: <20131030162342.GA21211@kroah.com>
Date:	Wed, 30 Oct 2013 09:23:42 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tim Gardner <tim.gardner@...onical.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Gleb Natapov <gleb@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM list <kvm@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 3.12-rc7] KVM: Fix modprobe failure for kvm_intel/kvm_amd

On Wed, Oct 30, 2013 at 05:08:09PM +0100, Paolo Bonzini wrote:
> Il 30/10/2013 16:59, Greg KH ha scritto:
> >> > Even if it is okay to exit and not create the files (and I think it's a
> >> > bit surprising), I'd like at least a printk to signal what's happening.
> >> >  But there should be no reason for debugfs directory creation to fail in
> >> > the end, except for basic mistakes such as the one that Tim reported, so
> >> > I think it's better to report the failure.
> > Creation will "fail" if debugfs is not enabled, so spiting out printk
> > messages in that case is not a good idea.
> 
> Interestingly, if debugfs is not enabled we are already returning an
> error-valued pointer:
> 
> static inline struct dentry *debugfs_create_dir(const char *name,
>                                                 struct dentry *parent)
> {
>         return ERR_PTR(-ENODEV);
> }
> 
> which would oops a lot of the current callers.

It will oops?  Really?  Where?  That shouldn't happen at all.

> Very few places use the currently correct idiom
> 
> 	if (IS_ERR(root) || !root)
> 
> but it's very ugly...  Perhaps debugfs_create_dir *should* return an
> error-valued pointer after all.

Or just don't care about the return value, and all will work out just
fine, right?

thanks,

greg k-h
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