From: Sean Christopherson <seanjc@google.com>
To: Ackerley Tng <ackerleytng@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Shuah Khan <skhan@linuxfoundation.org>,
Tianrui Zhao <zhaotianrui@loongson.cn>,
Bibo Mao <maobibo@loongson.cn>,
Huacai Chen <chenhuacai@kernel.org>,
WANG Xuerui <kernel@xen0n.name>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Fuad Tabba <tabba@google.com>,
vannapurve@google.com, x86@kernel.org,
"H. Peter Anvin" <hpa@zytor.com>,
kvm@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, loongarch@lists.linux.dev
Subject: Re: [PATCH RFC 07/12] Documentation: KVM: Drop mention of kvm->lock in SRCU documentation
Date: Thu, 25 Jun 2026 11:35:34 -0700 [thread overview]
Message-ID: <aj109naG1wr46Cpf@google.com> (raw)
In-Reply-To: <20260527-kvm-locking-docs-v1-7-4fe8b602ff47@google.com>
On Wed, May 27, 2026, Ackerley Tng wrote:
> The original comment says that synchronize_srcu(&kvm->srcu) is called
> inside critical sections for kvm->lock, vcpu->mutex and
> kvm->slots_lock. Drop mention of kvm->lock since this is no longer true.
I would *much* rather "fix" this by saying synchronize_srcu() *may* be called
inside blah blah blah. Because (a) I don't feel like auditing all of KVM to see
if the above is true, (b) KVM's implementation may change again in the future,
and (c) taking kvm->lock inside a kvm->srcu read-side critical section is still
unsafe as we'd end up with ABBA deadlock (well, ABCCA?).
1. SRCU held, waiting on kvm->lock
2. kvm->lock held, waiting on vcpu->mutex
3. vcpu->mutex held, waiting on synchronize_srcu()
next prev parent reply other threads:[~2026-06-25 18:35 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-27 15:33 [PATCH RFC 00/12] Document synchronization used in managing guest faults Ackerley Tng via B4 Relay
2026-05-27 15:33 ` [PATCH RFC 01/12] Documentation: KVM: Elaborate comment on kvm_usage_lock Ackerley Tng via B4 Relay
2026-06-25 18:12 ` Sean Christopherson
2026-05-27 15:33 ` [PATCH RFC 02/12] Documentation: KVM: Consolidate notes about cpu_read_lock() and kvm_lock Ackerley Tng via B4 Relay
2026-06-25 18:12 ` Sean Christopherson
2026-05-27 15:33 ` [PATCH RFC 03/12] Documentation: KVM: Consolidate notes about kvm->slots_lock and irq_lock Ackerley Tng via B4 Relay
2026-06-25 18:12 ` Sean Christopherson
2026-05-27 15:33 ` [PATCH RFC 04/12] Documentation: KVM: Turn - into bullet point Ackerley Tng via B4 Relay
2026-05-27 15:33 ` [PATCH RFC 05/12] Documentation: KVM: Explain what rule the exception section is meant for Ackerley Tng via B4 Relay
2026-05-27 15:33 ` [PATCH RFC 06/12] Documentation: KVM: Have actual headings for exceptions Ackerley Tng via B4 Relay
2026-05-27 15:40 ` sashiko-bot
2026-05-27 15:33 ` [PATCH RFC 07/12] Documentation: KVM: Drop mention of kvm->lock in SRCU documentation Ackerley Tng via B4 Relay
2026-06-25 18:35 ` Sean Christopherson [this message]
2026-05-27 15:33 ` [PATCH RFC 08/12] Documentation: KVM: Add example for kvm->srcu in relation to mutex/lock Ackerley Tng via B4 Relay
2026-06-25 18:17 ` Sean Christopherson
2026-05-27 15:33 ` [PATCH RFC 09/12] Documentation: KVM: Document synchronization for managing guest faults Ackerley Tng via B4 Relay
2026-05-27 15:33 ` [PATCH RFC 10/12] KVM: guest_memfd: Clarify comment about gmem.file vs kvm->srcu Ackerley Tng via B4 Relay
2026-06-25 18:19 ` Sean Christopherson
2026-05-27 15:33 ` [PATCH RFC 11/12] KVM: mmu: Point users of host_pfn_mapping_level() to docs Ackerley Tng via B4 Relay
2026-06-25 18:29 ` Sean Christopherson
2026-05-27 15:33 ` [PATCH RFC 12/12] Documentation: KVM: Focus acquisition order section on preventing deadlocks Ackerley Tng via B4 Relay
2026-06-25 18:25 ` Sean Christopherson
2026-06-25 18:37 ` [PATCH RFC 00/12] Document synchronization used in managing guest faults Sean Christopherson
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