From bf3d32e1156c36c88b75960fd2e5457d5d75620b Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Sat, 16 Nov 2013 17:46:04 +1100 Subject: [PATCH] KVM: PPC: Book3S HV: Make tbacct_lock irq-safe Lockdep reported that there is a potential for deadlock because vcpu->arch.tbacct_lock is not irq-safe, and is sometimes taken inside the rq_lock (run-queue lock) in the scheduler, which is taken within interrupts. The lockdep splat looks like: ====================================================== [ INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected ] 3.12.0-rc5-kvm+ #8 Not tainted ------------------------------------------------------ qemu-system-ppc/4803 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire: (&(&vcpu->arch.tbacct_lock)->rlock){+.+...}, at: [] .kvmppc_core_vcpu_put_hv+0x2c/0xa0 and this task is already holding: (&rq->lock){-.-.-.}, at: [] .__schedule+0x180/0xaa0 which would create a new lock dependency: (&rq->lock){-.-.-.} -> (&(&vcpu->arch.tbacct_lock)->rlock){+.+...} but this new dependency connects a HARDIRQ-irq-safe lock: (&rq->lock){-.-.-.} ... which became HARDIRQ-irq-safe at: [] .lock_acquire+0xbc/0x190 [] ._raw_spin_lock+0x34/0x60 [] .scheduler_tick+0x54/0x180 [] .update_process_times+0x70/0xa0 [] .tick_periodic+0x3c/0xe0 [] .tick_handle_periodic+0x28/0xb0 [] .timer_interrupt+0x120/0x2e0 [] decrementer_common+0x168/0x180 [] .get_page_from_freelist+0x924/0xc10 [] .__alloc_pages_nodemask+0x200/0xba0 [] .alloc_pages_exact_nid+0x68/0x110 [] .page_cgroup_init+0x1e0/0x270 [] .start_kernel+0x3e0/0x4e4 [] .start_here_common+0x20/0x70 to a HARDIRQ-irq-unsafe lock: (&(&vcpu->arch.tbacct_lock)->rlock){+.+...} ... which became HARDIRQ-irq-unsafe at: ... [] .lock_acquire+0xbc/0x190 [] ._raw_spin_lock+0x34/0x60 [] .kvmppc_core_vcpu_load_hv+0x2c/0x100 [] .kvmppc_core_vcpu_load+0x2c/0x40 [] .kvm_arch_vcpu_load+0x10/0x30 [] .vcpu_load+0x64/0xd0 [] .kvm_vcpu_ioctl+0x68/0x730 [] .do_vfs_ioctl+0x4dc/0x7a0 [] .SyS_ioctl+0xc4/0xe0 [] syscall_exit+0x0/0x98 Some users have reported this deadlock occurring in practice, though the reports have been primarily on 3.10.x-based kernels. This fixes the problem by making tbacct_lock be irq-safe. Signed-off-by: Paul Mackerras Signed-off-by: Alexander Graf --- arch/powerpc/kvm/book3s_hv.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-) diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 072287f1c3bc..31d9cfb64a23 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -131,8 +131,9 @@ static void kvmppc_fast_vcpu_kick_hv(struct kvm_vcpu *vcpu) 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(&vcpu->arch.tbacct_lock); + 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; @@ -143,19 +144,20 @@ static void kvmppc_core_vcpu_load_hv(struct kvm_vcpu *vcpu, int cpu) vcpu->arch.busy_stolen += mftb() - vcpu->arch.busy_preempt; vcpu->arch.busy_preempt = TB_NIL; } - spin_unlock(&vcpu->arch.tbacct_lock); + spin_unlock_irqrestore(&vcpu->arch.tbacct_lock, flags); } static void kvmppc_core_vcpu_put_hv(struct kvm_vcpu *vcpu) { struct kvmppc_vcore *vc = vcpu->arch.vcore; + unsigned long flags; - spin_lock(&vcpu->arch.tbacct_lock); + spin_lock_irqsave(&vcpu->arch.tbacct_lock, flags); if (vc->runner == vcpu && vc->vcore_state != VCORE_INACTIVE) vc->preempt_tb = mftb(); if (vcpu->arch.state == KVMPPC_VCPU_BUSY_IN_HOST) vcpu->arch.busy_preempt = mftb(); - spin_unlock(&vcpu->arch.tbacct_lock); + spin_unlock_irqrestore(&vcpu->arch.tbacct_lock, flags); } static void kvmppc_set_msr_hv(struct kvm_vcpu *vcpu, u64 msr) @@ -486,11 +488,11 @@ static u64 vcore_stolen_time(struct kvmppc_vcore *vc, u64 now) */ if (vc->vcore_state != VCORE_INACTIVE && vc->runner->arch.run_task != current) { - spin_lock(&vc->runner->arch.tbacct_lock); + 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(&vc->runner->arch.tbacct_lock); + spin_unlock_irq(&vc->runner->arch.tbacct_lock); } else { p = vc->stolen_tb; } @@ -512,10 +514,10 @@ static void kvmppc_create_dtl_entry(struct kvm_vcpu *vcpu, core_stolen = vcore_stolen_time(vc, now); stolen = core_stolen - vcpu->arch.stolen_logged; vcpu->arch.stolen_logged = core_stolen; - spin_lock(&vcpu->arch.tbacct_lock); + spin_lock_irq(&vcpu->arch.tbacct_lock); stolen += vcpu->arch.busy_stolen; vcpu->arch.busy_stolen = 0; - spin_unlock(&vcpu->arch.tbacct_lock); + spin_unlock_irq(&vcpu->arch.tbacct_lock); if (!dt || !vpa) return; memset(dt, 0, sizeof(struct dtl_entry)); @@ -1115,13 +1117,13 @@ static void kvmppc_remove_runnable(struct kvmppc_vcore *vc, if (vcpu->arch.state != KVMPPC_VCPU_RUNNABLE) return; - spin_lock(&vcpu->arch.tbacct_lock); + spin_lock_irq(&vcpu->arch.tbacct_lock); now = mftb(); vcpu->arch.busy_stolen += vcore_stolen_time(vc, now) - vcpu->arch.stolen_logged; vcpu->arch.busy_preempt = now; vcpu->arch.state = KVMPPC_VCPU_BUSY_IN_HOST; - spin_unlock(&vcpu->arch.tbacct_lock); + spin_unlock_irq(&vcpu->arch.tbacct_lock); --vc->n_runnable; list_del(&vcpu->arch.run_list); } -- GitLab