2017-08-01 14:22+0200, Paolo Bonzini: > On 01/08/2017 14:20, Wanpeng Li wrote: > > From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > > > > WARNING: CPU: 5 PID: 1242 at kernel/rcu/tree_plugin.h:323 rcu_note_context_switch+0x207/0x6b0 > > CPU: 5 PID: 1242 Comm: unity-settings- Not tainted 4.13.0-rc2+ #1 > > RIP: 0010:rcu_note_context_switch+0x207/0x6b0 > > Call Trace: > > __schedule+0xda/0xba0 > > ? kvm_async_pf_task_wait+0x1b2/0x270 > > schedule+0x40/0x90 > > kvm_async_pf_task_wait+0x1cc/0x270 > > ? prepare_to_swait+0x22/0x70 > > do_async_page_fault+0x77/0xb0 > > ? do_async_page_fault+0x77/0xb0 > > async_page_fault+0x28/0x30 > > RIP: 0010:__d_lookup_rcu+0x90/0x1e0 > > > > I encounter this when trying to stress the async page fault in L1 guest w/ > > L2 guests running. > > > > 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 is not accurate anymore: > > 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. However, > we need to call the pair even if the function calls schedule(), as seen > from the above backtrace. > > Can be fixed when committing. Done that, thanks.