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From: Peter Zijlstra <peterz@infradead.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>,
	kvm@vger.kernel.org,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Guo Ren <guoren@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	linux-riscv@lists.infradead.org,
	Vincent Chen <deanbo422@gmail.com>, Will Deacon <will@kernel.org>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	xen-devel@lists.xenproject.org, Marc Zyngier <maz@kernel.org>,
	Joerg Roedel <joro@8bytes.org>,
	x86@kernel.org, Russell King <linux@armlinux.org.uk>,
	linux-csky@vger.kernel.org, kvmarm@lists.cs.columbia.edu,
	Ingo Molnar <mingo@redhat.com>, Like Xu <like.xu.linux@gmail.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Zhu Lingshan <lingshan.zhu@intel.com>,
	Jiri Olsa <jolsa@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Borislav Petkov <bp@alien8.de>, Greentime Hu <green.hu@gmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Artem Kashkanov <artem.kashkanov@intel.com>,
	linux-arm-kernel@lists.infradead.org,
	Jim Mattson <jmattson@google.com>,
	Juergen Gross <jgross@suse.com>,
	Like Xu <like.xu@linux.intel.com>, Nick Hu <nickhu@andestech.com>,
	linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH v4 01/17] perf: Protect perf_guest_cbs with RCU
Date: Thu, 11 Nov 2021 11:47:57 +0100	[thread overview]
Message-ID: <YYz03fcDRV9NZnyA@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <d784dc27-72d0-d64f-e1f4-a2b9a5f86dd4@redhat.com>

On Thu, Nov 11, 2021 at 08:26:58AM +0100, Paolo Bonzini wrote:
> On 11/11/21 03:07, Sean Christopherson wrote:

> >   EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
> >   int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
> >   {
> > -	perf_guest_cbs = NULL;
> > +	if (WARN_ON_ONCE(rcu_access_pointer(perf_guest_cbs) != cbs))
> > +		return -EINVAL;
> > +
> > +	rcu_assign_pointer(perf_guest_cbs, NULL);
> > +	synchronize_rcu();
> 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.

There's a very few sites where we use RCU_INIT_POINTER() with a !NULL
argument, and those are 'special'.
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  reply	other threads:[~2021-11-11 10:48 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-11  2:07 [PATCH v4 00/17] perf: KVM: Fix, optimize, and clean up callbacks Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 01/17] perf: Protect perf_guest_cbs with RCU Sean Christopherson
2021-11-11  7:26   ` Paolo Bonzini
2021-11-11 10:47     ` Peter Zijlstra [this message]
2021-11-12  7:55       ` Paolo Bonzini
2021-11-11  2:07 ` [PATCH v4 02/17] KVM: x86: Register perf callbacks after calling vendor's hardware_setup() Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 03/17] KVM: x86: Register Processor Trace interrupt hook iff PT enabled in guest Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 04/17] perf: Stop pretending that perf can handle multiple guest callbacks Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 05/17] perf: Drop dead and useless guest "support" from arm, csky, nds32 and riscv Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 06/17] perf/core: Rework guest callbacks to prepare for static_call support Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 07/17] perf: Add wrappers for invoking guest callbacks Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 08/17] perf: Force architectures to opt-in to " Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 09/17] perf/core: Use static_call to optimize perf_guest_info_callbacks Sean Christopherson
2022-02-02 18:43   ` Sean Christopherson
2022-02-04 17:35     ` Sami Tolvanen
2022-02-06 13:08       ` Peter Zijlstra
2022-02-06 18:45       ` Kees Cook
2022-02-06 20:28         ` Peter Zijlstra
2022-02-07  2:55           ` Kees Cook
2022-02-18 22:35             ` Will McVicker
2022-08-24 16:45               ` Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 10/17] KVM: x86: Drop current_vcpu for kvm_running_vcpu + kvm_arch_vcpu variable Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 11/17] KVM: x86: More precisely identify NMI from guest when handling PMI Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 12/17] KVM: Move x86's perf guest info callbacks to generic KVM Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 13/17] KVM: x86: Move Intel Processor Trace interrupt handler to vmx.c Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 14/17] KVM: arm64: Convert to the generic perf callbacks Sean Christopherson
2021-11-11  2:07 ` [PATCH v4 15/17] KVM: arm64: Hide kvm_arm_pmu_available behind CONFIG_HW_PERF_EVENTS=y Sean Christopherson
2021-11-11 21:49   ` Marc Zyngier
2021-11-11  2:07 ` [PATCH v4 16/17] KVM: arm64: Drop perf.c and fold its tiny bits of code into arm.c Sean Christopherson
2021-11-11 21:49   ` Marc Zyngier
2021-11-11  2:07 ` [PATCH v4 17/17] perf: Drop guest callback (un)register stubs Sean Christopherson
2021-11-11 11:19 ` [PATCH v4 00/17] perf: KVM: Fix, optimize, and clean up callbacks Peter Zijlstra

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