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Subject: Re: [PATCH] KVM: Add separate helper for putting borrowed reference
 to kvm
To:     Leonardo Bras <leonardo@linux.ibm.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     Paul Mackerras <paulus@ozlabs.org>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        kvm-ppc@vger.kernel.org, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20191021225842.23941-1-sean.j.christopherson@intel.com>
 <de313d549a5ae773aad6bbf04c20b395bea7811f.camel@linux.ibm.com>
 <20191126171416.GA22233@linux.intel.com>
 <0009c6c1bb635098fa68cb6db6414634555039fe.camel@linux.ibm.com>
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 <bfa563e6a584bd85d3abe953ca088281dc0e167b.camel@linux.ibm.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <6beeff56-7676-5dfd-a578-1732730f8963@redhat.com>
Date:   Wed, 27 Nov 2019 19:32:32 +0100
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On 27/11/19 19:24, Leonardo Bras wrote:
> By what I could undestand up to now, these functions that use borrowed
> references can only be called while the reference (file descriptor)
> exists.=20
> So, suppose these threads, where:
> - T1 uses a borrowed reference, and=20
> - T2 is releasing the reference (close, release):

Nit: T2 is releasing the *last* reference (as implied by your reference
to close/release).

>=20
> T1=09=09=09=09| T2
> kvm_get_kvm()=09=09=09|
> ...=09=09=09=09| kvm_put_kvm()
> kvm_put_kvm_no_destroy()=09|
>=20
> The above would not trigger a use-after-free bug, but will cause a
> memory leak. Is my above understanding right?

Yes, this is correct.

Paolo


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