linux-kernel - Re: [RFC PATCH kernel] KVM: Stop leaking memory in debugfs

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Message-ID: <CABgObfamvoMai1b9hrPkt1uwgw0kozhU5V_Vvk1__k_sGnx4LA@mail.gmail.com>
Date:   Tue, 3 Aug 2021 15:29:16 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Alexey Kardashevskiy <aik@...abs.ru>,
        "Kernel Mailing List, Linux" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>
Subject: Re: [RFC PATCH kernel] KVM: Stop leaking memory in debugfs

> So userspace can create kvm resources with duplicate names?  That feels
> wrong to me.

Yes, the name is just the (pid, file descriptor). It's used only for
debugfs, and it's not really likely going to happen unless a program
does it on purpose, but the ugliness/wrongness is one of the reasons
why we now have a non-debugfs mechanism to retrieve the stats.

> But if all that is "duplicate" is the debugfs kvm directory, why not ask
> debugfs if it is already present before trying to create it again?  That
> way you will not have debugfs complain about duplicate
> files/directories.

That would also be racy; it would need a simple mutex around
debugfs_lookup and debugfs_create_dir. But it would indeed avoid the
complaints altogether, so I'll prepare a patch.  Thanks,

Paolo