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SubjectRe: [PATCH v4] KVM: async_pf: make rcu irq exit if not triggered from idle task
2017-08-01 14:22+0200, Paolo Bonzini:
> On 01/08/2017 14:20, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpeng.li@hotmail.com>
> >
> > 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.

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