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

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Date:	Tue, 29 Oct 2013 13:00:12 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Cc:	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>,
	Paolo Bonzini <pbonzini@...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 12:57:32AM +0530, Raghavendra K T wrote:
> Adding Greg/AI too since we touch debugfs code.

You do?

> [...]
> >>
> >>sudo modprobe kvm_amd
> >>modprobe: ERROR: could not insert 'kvm_amd': Bad address
> >
> >"Bad address"? Christ people, are you guys making up error numbers
> >with some kind of dice-roll? I can just see it now, somebody sitting
> >there with a D20, playing some kind of kernel-specific D&D, and
> >rolling a ten means that you get to slay the orc, and pick an error
> >number of EFAULT for some random kernel function. Because quite
> >frankly, "random dice roll" is the _only_ thing that explains "Bad
> >address" sufficiently.
> >
> >Please, whoever wrote virt/kvm/kvm_main.c:: kvm_init_debug(), WTF?
> >EFAULT means "user passed in an invalid virtual address pointer",
> >which is why the error string is "Bad address". It makes absolutely NO
> >SENSE here. Perhaps EEXIST or EBUSY.
> >
> 
> Right. In current scenario it should have been EEXIST :(.
> 
> debugfs_create_dir() currently returns NULL dentry on both
> EEXIST, ENOMEM ... cases.
> 
> Could one solution be cascading actual error
> that is lost in fs/debugfs/inode.c:__create_file(), so that we could
> take correct action in case of failure of debugfs_create_dir()?

What would you do here?  You shouldn't really care about debugfs files,
if there's an error, keep on going, no code path should really care,
right?

thanks,

greg k-h
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