linux-kernel - Re: [PATCH v4 01/17] perf: Protect perf_guest

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Message-ID: <016d5b91-6910-2aca-0db1-a65079449454@redhat.com>
Date:   Fri, 12 Nov 2021 08:55:31 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Guo Ren <guoren@...nel.org>, Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
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        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
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        Suzuki K Poulose <suzuki.poulose@....com>,
        "H. Peter Anvin" <hpa@...or.com>,
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        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-csky@...r.kernel.org, linux-riscv@...ts.infradead.org,
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        Artem Kashkanov <artem.kashkanov@...el.com>,
        Like Xu <like.xu.linux@...il.com>,
        Like Xu <like.xu@...ux.intel.com>,
        Zhu Lingshan <lingshan.zhu@...el.com>
Subject: Re: [PATCH v4 01/17] perf: Protect perf_guest_cbs with RCU

On 11/11/21 11:47, Peter Zijlstra wrote:
>> This technically could be RCU_INIT_POINTER but it's not worth a respin.
>> There are dozens of other occurrences, and if somebody wanted they
>> could use Coccinelle to fix all of them.
> I've been pushing the other way, trying to get rid of RCU_INIT_POINTER()
> since rcu_assign_pointer(, NULL) actualy DTRT per __builtin_constant_p()
> etc.

Oh, that's pretty cool to know, thanks!

Paolo

> There's a very few sites where we use RCU_INIT_POINTER() with a !NULL
> argument, and those are 'special'.
>