Marcelo Tosatti wrote: > On Mon, Apr 19, 2010 at 01:08:29PM +0300, Avi Kivity wrote: >> On 04/19/2010 12:58 PM, Lai Jiangshan wrote: >>> Applied the patch I just sent and let CONFIG_PROVE_RCU=y, >>> we can got the following dmesg. And we found that it is >>> because some codes in KVM dereferences srcu-protected pointer without >>> srcu_read_lock() held or update-side lock held. >>> >>> It is not hard to fix, the problem is that: >>> Where is the most proper place to put a srcu_read_lock()? >>> >>> I can not determine the answer, so I report this bug >>> instead of fixing it. >>> >> I think the else branch in complete_pio() should work. Marcelo? >> >> Longer term I'd like to see the lock taken at the high levels >> (ioctls, in virt/kvm) and dropped only for guest entry and when we >> explicitly sleep (hlt emulation). >> >> Note: complete_pio() is gone in the current code. > > Yes, this was fixed by 7fb2ea1e6. > > Applied the patch I sent yesterday and let CONFIG_PROVE_RCU=y I can get the following dmesg. Under very simple test, these is no complaint from PROVE_RCU after this patch applied. More test or reviewing of code are need in future. ---------- Subject: [PATCH] kvm: add missing srcu_read_lock() I got this dmesg due to srcu_read_lock() is missing in kvm_mmu_notifier_release(). =================================================== [ INFO: suspicious rcu_dereference_check() usage. ] --------------------------------------------------- arch/x86/kvm/x86.h:72 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 0 2 locks held by qemu-system-x86/3100: #0: (rcu_read_lock){.+.+..}, at: [<ffffffff810d73dc>] __mmu_notifier_release+0x38/0xdf #1: (&(&kvm->mmu_lock)->rlock){+.+...}, at: [<ffffffffa0130a6a>] kvm_mmu_zap_all+0x21/0x5e [kvm] stack backtrace: Pid: 3100, comm: qemu-system-x86 Not tainted 2.6.34-rc3-22949-gbc8a97a-dirty #2 Call Trace: [<ffffffff8106afd9>] lockdep_rcu_dereference+0xaa/0xb3 [<ffffffffa0123a89>] unalias_gfn+0x56/0xab [kvm] [<ffffffffa0119600>] gfn_to_memslot+0x16/0x25 [kvm] [<ffffffffa012ffca>] gfn_to_rmap+0x17/0x6e [kvm] [<ffffffffa01300c1>] rmap_remove+0xa0/0x19d [kvm] [<ffffffffa0130649>] kvm_mmu_zap_page+0x109/0x34d [kvm] [<ffffffffa0130a7e>] kvm_mmu_zap_all+0x35/0x5e [kvm] [<ffffffffa0122870>] kvm_arch_flush_shadow+0x16/0x22 [kvm] [<ffffffffa01189e0>] kvm_mmu_notifier_release+0x15/0x17 [kvm] [<ffffffff810d742c>] __mmu_notifier_release+0x88/0xdf [<ffffffff810d73dc>] ? __mmu_notifier_release+0x38/0xdf [<ffffffff81040848>] ? exit_mm+0xe0/0x115 [<ffffffff810c2cb0>] exit_mmap+0x2c/0x17e [<ffffffff8103c472>] mmput+0x2d/0xd4 [<ffffffff81040870>] exit_mm+0x108/0x115 [...] Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx> --- diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index a5dfea1..a6d639d 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -341,7 +341,11 @@ static void kvm_mmu_notifier_release(struct mmu_notifier *mn, struct mm_struct *mm) { struct kvm *kvm = mmu_notifier_to_kvm(mn); + int idx; + + idx = srcu_read_lock(&kvm->srcu); kvm_arch_flush_shadow(kvm); + srcu_read_unlock(&kvm->srcu, idx); } static const struct mmu_notifier_ops kvm_mmu_notifier_ops = { -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html