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[34.82.80.254]) by smtp.gmail.com with ESMTPSA id n14sm34009pjv.34.2021.07.26.09.53.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Jul 2021 09:53:57 -0700 (PDT) Date: Mon, 26 Jul 2021 16:53:53 +0000 From: David Matlack To: Dan Carpenter Cc: bgardon@google.com, kvm@vger.kernel.org Subject: Re: [bug report] KVM: x86/mmu: Use an rwlock for the x86 MMU Message-ID: References: <20210726075238.GA10030@kili> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210726075238.GA10030@kili> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Jul 26, 2021 at 10:52:38AM +0300, Dan Carpenter wrote: > [ This is not the correct patch to blame, but there is something going > on here which I don't understand so this email is more about me > learning rather than reporting bugs. - dan ] > > Hello Ben Gardon, > > The patch 531810caa9f4: "KVM: x86/mmu: Use an rwlock for the x86 MMU" > from Feb 2, 2021, leads to the following static checker warning: > > arch/x86/kvm/mmu/mmu.c:5769 kvm_mmu_zap_all() > warn: sleeping in atomic context > > arch/x86/kvm/mmu/mmu.c > 5756 void kvm_mmu_zap_all(struct kvm *kvm) > 5757 { > 5758 struct kvm_mmu_page *sp, *node; > 5759 LIST_HEAD(invalid_list); > 5760 int ign; > 5761 > 5762 write_lock(&kvm->mmu_lock); > ^^^^^^^^^^^^^^^^^^^^^^^^^^ > This line bumps the preempt count. > > 5763 restart: > 5764 list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) { > 5765 if (WARN_ON(sp->role.invalid)) > 5766 continue; > 5767 if (__kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list, &ign)) > 5768 goto restart; > --> 5769 if (cond_resched_rwlock_write(&kvm->mmu_lock)) > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > This line triggers a sleeping in atomic warning. What's going on here > that I'm not understanding? cond_resched_rwlock_write drops the provided lock (kvm->mmu_lock in this case) before scheduling and then re-acquires it afterwards. So this warning looks like a false positive. > > 5770 goto restart; > 5771 } > 5772 > 5773 kvm_mmu_commit_zap_page(kvm, &invalid_list); > 5774 > 5775 if (is_tdp_mmu_enabled(kvm)) > 5776 kvm_tdp_mmu_zap_all(kvm); > 5777 > 5778 write_unlock(&kvm->mmu_lock); > 5779 } > > regards, > dan carpenter