Andrea Arcangeli wrote: > Ok, I think I found one first deadlock source during swapping with the > mmu notifiers and it's a KVM bug. I got a deadlock inversion between > PT lock and mmu_lock because of this bug. With PREEMPT=n it's not > enough to spin_lock(mmu_lock) to disable preempt and in turn the page > fault will go through and it'll take the PT lock _after_ the mmu_lock > which is a forbidden ordering (the VM often calls the mmu notifier > invalidate page with the PT lock held). For example FNAME(fetch) calls > kvm_read_guest_atomic with the mmu_lock held (taken by > FNAME(page_fault)). Not sure why I didn't trigger yet on my > workstation but only on the test system. This seem not enough to get > V2 stable yet (but I think it was enough to get my old codebase stable > on the test system). I'll now try to rollback kvm source to my last > stable status and to apply this fix and run it on V2/V3. > > Signed-off-by: Andrea Arcangeli <[EMAIL PROTECTED]> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 8fc12dc..48d9a11 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -553,7 +565,9 @@ int kvm_read_guest_atomic(struct kvm *kvm, gpa_t gpa, > void *data, > addr = gfn_to_hva(kvm, gfn); > if (kvm_is_error_hva(addr)) > return -EFAULT; > + pagefault_disable(); > r = __copy_from_user_inatomic(data, (void __user *)addr + offset, len); > + pagefault_enable(); > if (r) > return -EFAULT; > return 0; >
This is surprising. pagefault_disable() is really a preempt_disable(), and kvm_read_guest_atomic() should only be called from atomic contexts (with preemption already disabled), no? -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
