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

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Message-ID: <52700C24.9050001@linux.vnet.ibm.com>
Date:	Wed, 30 Oct 2013 00:57:32 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg KH <gregkh@...uxfoundation.org>
CC:	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

Adding Greg/AI too since we touch debugfs code.
[...]
 >>
>> 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()?

(ugly side is we increase total number of params for __create_file to
6). or I hope there could be some better solution.

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