| Message ID | 1496837040-8200-1-git-send-email-wanpeng.li@hotmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 07/06/2017 14:04, Wanpeng Li wrote: > From: Wanpeng Li <wanpeng.li@hotmail.com> > > Commit 9b132fbe5419 (Add rcu user eqs exception hooks for async page fault) > adds rcu_irq_enter/exit() to kvm_async_pf_task_wait() to exit cpu idle eqs > when needed, to protect the code that needs use rcu. There is no need to call > this pairs if async page fault is not triggered from idle task. > > This patch fixes it by rcu irq exit if it is not triggered from idle task to > avoid rcu hang after schedule() in the for loop. How does the bug manifest? Paolo > > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> > --- > arch/x86/kernel/kvm.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 43e10d6..e70ed72 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -141,6 +141,8 @@ void kvm_async_pf_task_wait(u32 token) > n.token = token; > n.cpu = smp_processor_id(); > n.halted = is_idle_task(current) || preempt_count() > 1; > + if (!n.halted) > + rcu_irq_exit(); > init_swait_queue_head(&n.wq); > hlist_add_head(&n.link, &b->list); > raw_spin_unlock(&b->lock); > @@ -167,8 +169,9 @@ void kvm_async_pf_task_wait(u32 token) > } > if (!n.halted) > finish_swait(&n.wq, &wait); > + else > + rcu_irq_exit(); > > - rcu_irq_exit(); > return; > }
2017-06-07 21:05 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>: > > > On 07/06/2017 14:04, Wanpeng Li wrote: >> From: Wanpeng Li <wanpeng.li@hotmail.com> >> >> Commit 9b132fbe5419 (Add rcu user eqs exception hooks for async page fault) >> adds rcu_irq_enter/exit() to kvm_async_pf_task_wait() to exit cpu idle eqs >> when needed, to protect the code that needs use rcu. There is no need to call >> this pairs if async page fault is not triggered from idle task. >> >> This patch fixes it by rcu irq exit if it is not triggered from idle task to >> avoid rcu hang after schedule() in the for loop. > > How does the bug manifest? Just by codes review. Regards, Wanpeng Li
On 07/06/2017 16:10, Wanpeng Li wrote: > 2017-06-07 21:05 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>: >> >> >> On 07/06/2017 14:04, Wanpeng Li wrote: >>> From: Wanpeng Li <wanpeng.li@hotmail.com> >>> >>> Commit 9b132fbe5419 (Add rcu user eqs exception hooks for async page fault) >>> adds rcu_irq_enter/exit() to kvm_async_pf_task_wait() to exit cpu idle eqs >>> when needed, to protect the code that needs use rcu. There is no need to call >>> this pairs if async page fault is not triggered from idle task. >>> >>> This patch fixes it by rcu irq exit if it is not triggered from idle task to >>> avoid rcu hang after schedule() in the for loop. >> >> How does the bug manifest? > > Just by codes review. So it's just code cleanup? Paolo
2017-06-07 22:24 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>: > > > On 07/06/2017 16:10, Wanpeng Li wrote: >> 2017-06-07 21:05 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>: >>> >>> >>> On 07/06/2017 14:04, Wanpeng Li wrote: >>>> From: Wanpeng Li <wanpeng.li@hotmail.com> >>>> >>>> Commit 9b132fbe5419 (Add rcu user eqs exception hooks for async page fault) >>>> adds rcu_irq_enter/exit() to kvm_async_pf_task_wait() to exit cpu idle eqs >>>> when needed, to protect the code that needs use rcu. There is no need to call >>>> this pairs if async page fault is not triggered from idle task. >>>> >>>> This patch fixes it by rcu irq exit if it is not triggered from idle task to >>>> avoid rcu hang after schedule() in the for loop. >>> >>> How does the bug manifest? >> >> Just by codes review. > > So it's just code cleanup? Yeah, this should be a cleanup and I will update the patch description. Actually, I observe a hang due to async pf injected to L2 which should be injected to L1, then tasks hang in L1 due to missing PAGE_READY async_pfs. Regards, Wanpeng Li
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 43e10d6..e70ed72 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -141,6 +141,8 @@ void kvm_async_pf_task_wait(u32 token) n.token = token; n.cpu = smp_processor_id(); n.halted = is_idle_task(current) || preempt_count() > 1; + if (!n.halted) + rcu_irq_exit(); init_swait_queue_head(&n.wq); hlist_add_head(&n.link, &b->list); raw_spin_unlock(&b->lock); @@ -167,8 +169,9 @@ void kvm_async_pf_task_wait(u32 token) } if (!n.halted) finish_swait(&n.wq, &wait); + else + rcu_irq_exit(); - rcu_irq_exit(); return; } EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait);