From 2711e248a352d7ecc8767b1dfa1f0c2356cb7f4b Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Thu, 4 Dec 2014 16:43:28 +1100 Subject: [PATCH] KVM: PPC: Book3S HV: Simplify locking around stolen time calculations Currently the calculations of stolen time for PPC Book3S HV guests uses fields in both the vcpu struct and the kvmppc_vcore struct. The fields in the kvmppc_vcore struct are protected by the vcpu->arch.tbacct_lock of the vcpu that has taken responsibility for running the virtual core. This works correctly but confuses lockdep, because it sees that the code takes the tbacct_lock for a vcpu in kvmppc_remove_runnable() and then takes another vcpu's tbacct_lock in vcore_stolen_time(), and it thinks there is a possibility of deadlock, causing it to print reports like this: ============================================= [ INFO: possible recursive locking detected ] 3.18.0-rc7-kvm-00016-g8db4bc6 #89 Not tainted --------------------------------------------- qemu-system-ppc/6188 is trying to acquire lock: (&(&vcpu->arch.tbacct_lock)->rlock){......}, at: [] .vcore_stolen_time+0x48/0xd0 [kvm_hv] but task is already holding lock: (&(&vcpu->arch.tbacct_lock)->rlock){......}, at: [] .kvmppc_remove_runnable.part.3+0x30/0xd0 [kvm_hv] other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&(&vcpu->arch.tbacct_lock)->rlock); lock(&(&vcpu->arch.tbacct_lock)->rlock); *** DEADLOCK *** May be due to missing lock nesting notation 3 locks held by qemu-system-ppc/6188: #0: (&vcpu->mutex){+.+.+.}, at: [] .vcpu_load+0x28/0xe0 [kvm] #1: (&(&vcore->lock)->rlock){+.+...}, at: [] .kvmppc_vcpu_run_hv+0x530/0x1530 [kvm_hv] #2: (&(&vcpu->arch.tbacct_lock)->rlock){......}, at: [] .kvmppc_remove_runnable.part.3+0x30/0xd0 [kvm_hv] stack backtrace: CPU: 40 PID: 6188 Comm: qemu-system-ppc Not tainted 3.18.0-rc7-kvm-00016-g8db4bc6 #89 Call Trace: [c000000b2754f3f0] [c000000000b31b6c] .dump_stack+0x88/0xb4 (unreliable) [c000000b2754f470] [c0000000000faeb8] .__lock_acquire+0x1878/0x2190 [c000000b2754f600] [c0000000000fbf0c] .lock_acquire+0xcc/0x1a0 [c000000b2754f6d0] [c000000000b2954c] ._raw_spin_lock_irq+0x4c/0x70 [c000000b2754f760] [d00000000ecb1fe8] .vcore_stolen_time+0x48/0xd0 [kvm_hv] [c000000b2754f7f0] [d00000000ecb25b4] .kvmppc_remove_runnable.part.3+0x44/0xd0 [kvm_hv] [c000000b2754f880] [d00000000ecb43ec] .kvmppc_vcpu_run_hv+0x76c/0x1530 [kvm_hv] [c000000b2754f9f0] [d00000000eb9f46c] .kvmppc_vcpu_run+0x2c/0x40 [kvm] [c000000b2754fa60] [d00000000eb9c9a4] .kvm_arch_vcpu_ioctl_run+0x54/0x160 [kvm] [c000000b2754faf0] [d00000000eb94538] .kvm_vcpu_ioctl+0x498/0x760 [kvm] [c000000b2754fcb0] [c000000000267eb4] .do_vfs_ioctl+0x444/0x770 [c000000b2754fd90] [c0000000002682a4] .SyS_ioctl+0xc4/0xe0 [c000000b2754fe30] [c0000000000092e4] syscall_exit+0x0/0x98 In order to make the locking easier to analyse, we change the code to use a spinlock in the kvmppc_vcore struct to protect the stolen_tb and preempt_tb fields. This lock needs to be an irq-safe lock since it is used in the kvmppc_core_vcpu_load_hv() and kvmppc_core_vcpu_put_hv() functions, which are called with the scheduler rq lock held, which is an irq-safe lock. Signed-off-by: Paul Mackerras Signed-off-by: Alexander Graf --- arch/powerpc/include/asm/kvm_host.h | 1 + arch/powerpc/kvm/book3s_hv.c | 60 +++++++++++++++++++------------------ 2 files changed, 32 insertions(+), 29 deletions(-) diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h index 0478556..7cf94a5 100644 --- a/arch/powerpc/include/asm/kvm_host.h +++ b/arch/powerpc/include/asm/kvm_host.h @@ -297,6 +297,7 @@ struct kvmppc_vcore { struct list_head runnable_threads; spinlock_t lock; wait_queue_head_t wq; + spinlock_t stoltb_lock; /* protects stolen_tb and preempt_tb */ u64 stolen_tb; u64 preempt_tb; struct kvm_vcpu *runner; diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 1a7a281..74afa2d 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -135,11 +135,10 @@ static void kvmppc_fast_vcpu_kick_hv(struct kvm_vcpu *vcpu) * stolen. * * Updates to busy_stolen are protected by arch.tbacct_lock; - * updates to vc->stolen_tb are protected by the arch.tbacct_lock - * of the vcpu that has taken responsibility for running the vcore - * (i.e. vc->runner). The stolen times are measured in units of - * timebase ticks. (Note that the != TB_NIL checks below are - * purely defensive; they should never fail.) + * updates to vc->stolen_tb are protected by the vcore->stoltb_lock + * lock. The stolen times are measured in units of timebase ticks. + * (Note that the != TB_NIL checks below are purely defensive; + * they should never fail.) */ static void kvmppc_core_vcpu_load_hv(struct kvm_vcpu *vcpu, int cpu) @@ -147,12 +146,21 @@ static void kvmppc_core_vcpu_load_hv(struct kvm_vcpu *vcpu, int cpu) struct kvmppc_vcore *vc = vcpu->arch.vcore; unsigned long flags; - spin_lock_irqsave(&vcpu->arch.tbacct_lock, flags); - if (vc->runner == vcpu && vc->vcore_state != VCORE_INACTIVE && - vc->preempt_tb != TB_NIL) { - vc->stolen_tb += mftb() - vc->preempt_tb; - vc->preempt_tb = TB_NIL; + /* + * We can test vc->runner without taking the vcore lock, + * because only this task ever sets vc->runner to this + * vcpu, and once it is set to this vcpu, only this task + * ever sets it to NULL. + */ + if (vc->runner == vcpu && vc->vcore_state != VCORE_INACTIVE) { + spin_lock_irqsave(&vc->stoltb_lock, flags); + if (vc->preempt_tb != TB_NIL) { + vc->stolen_tb += mftb() - vc->preempt_tb; + vc->preempt_tb = TB_NIL; + } + spin_unlock_irqrestore(&vc->stoltb_lock, flags); } + spin_lock_irqsave(&vcpu->arch.tbacct_lock, flags); if (vcpu->arch.state == KVMPPC_VCPU_BUSY_IN_HOST && vcpu->arch.busy_preempt != TB_NIL) { vcpu->arch.busy_stolen += mftb() - vcpu->arch.busy_preempt; @@ -166,9 +174,12 @@ static void kvmppc_core_vcpu_put_hv(struct kvm_vcpu *vcpu) struct kvmppc_vcore *vc = vcpu->arch.vcore; unsigned long flags; - spin_lock_irqsave(&vcpu->arch.tbacct_lock, flags); - if (vc->runner == vcpu && vc->vcore_state != VCORE_INACTIVE) + if (vc->runner == vcpu && vc->vcore_state != VCORE_INACTIVE) { + spin_lock_irqsave(&vc->stoltb_lock, flags); vc->preempt_tb = mftb(); + spin_unlock_irqrestore(&vc->stoltb_lock, flags); + } + spin_lock_irqsave(&vcpu->arch.tbacct_lock, flags); if (vcpu->arch.state == KVMPPC_VCPU_BUSY_IN_HOST) vcpu->arch.busy_preempt = mftb(); spin_unlock_irqrestore(&vcpu->arch.tbacct_lock, flags); @@ -505,25 +516,14 @@ static void kvmppc_update_vpas(struct kvm_vcpu *vcpu) static u64 vcore_stolen_time(struct kvmppc_vcore *vc, u64 now) { u64 p; + unsigned long flags; - /* - * If we are the task running the vcore, then since we hold - * the vcore lock, we can't be preempted, so stolen_tb/preempt_tb - * can't be updated, so we don't need the tbacct_lock. - * If the vcore is inactive, it can't become active (since we - * hold the vcore lock), so the vcpu load/put functions won't - * update stolen_tb/preempt_tb, and we don't need tbacct_lock. - */ + spin_lock_irqsave(&vc->stoltb_lock, flags); + p = vc->stolen_tb; if (vc->vcore_state != VCORE_INACTIVE && - vc->runner->arch.run_task != current) { - spin_lock_irq(&vc->runner->arch.tbacct_lock); - p = vc->stolen_tb; - if (vc->preempt_tb != TB_NIL) - p += now - vc->preempt_tb; - spin_unlock_irq(&vc->runner->arch.tbacct_lock); - } else { - p = vc->stolen_tb; - } + vc->preempt_tb != TB_NIL) + p += now - vc->preempt_tb; + spin_unlock_irqrestore(&vc->stoltb_lock, flags); return p; } @@ -1359,6 +1359,7 @@ static struct kvmppc_vcore *kvmppc_vcore_create(struct kvm *kvm, int core) INIT_LIST_HEAD(&vcore->runnable_threads); spin_lock_init(&vcore->lock); + spin_lock_init(&vcore->stoltb_lock); init_waitqueue_head(&vcore->wq); vcore->preempt_tb = TB_NIL; vcore->lpcr = kvm->arch.lpcr; @@ -1696,6 +1697,7 @@ static void kvmppc_run_core(struct kvmppc_vcore *vc) vc->n_woken = 0; vc->nap_count = 0; vc->entry_exit_count = 0; + vc->preempt_tb = TB_NIL; vc->vcore_state = VCORE_STARTING; vc->in_guest = 0; vc->napping_threads = 0; -- 2.7.4