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
