On 07/11/2017 00:03, Ben Hutchings wrote:
> 3.16.50-rc1 review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> commit 337c017ccdf2653d0040099433fc1a2b1beb5926 upstream.
>
> 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. However,
> we need to call the pair even if the function calls schedule(), as seen
> from the above backtrace.
>
> This patch fixes it by informing the RCU subsystem exit/enter the irq
> towards/away from idle for both n.halted and !n.halted.
>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
> ---
> arch/x86/kernel/kvm.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -150,6 +150,8 @@ void kvm_async_pf_task_wait(u32 token)
> if (hlist_unhashed(&n.link))
> break;
>
> + rcu_irq_exit();
> +
> if (!n.halted) {
> local_irq_enable();
> schedule();
> @@ -158,11 +160,11 @@ void kvm_async_pf_task_wait(u32 token)
> /*
> * We cannot reschedule. So halt.
> */
> - rcu_irq_exit();
> native_safe_halt();
> local_irq_disable();
> - rcu_irq_enter();
> }
> +
> + rcu_irq_enter();
> }
> if (!n.halted)
> finish_wait(&n.wq, &wait);
>
Looks good, please backport
b862789aa5186d5ea3a024b7cfe0f80c3a38b980 and
a2b7861bb33b2538420bb5d8554153484d3f961f
as well.
Thanks,
Paolo