Re: [PATCH v4 1/2] rcu: Introduce force_rcu notifier

[Richard Henderson <richard.henderson@linaro.org>]

On 11/9/21 7:35 PM, Greg Kurz wrote:
> The drain_rcu_call() function can be blocked as long as an RCU reader
> stays in a read-side critical section. This is typically what happens
> when a TCG vCPU is executing a busy loop. It can deadlock the QEMU
> monitor as reported inhttps://gitlab.com/qemu-project/qemu/-/issues/650  .
> 
> This can be avoided by allowing drain_rcu_call() to enforce an RCU grace
> period. Since each reader might need to do specific actions to end a
> read-side critical section, do it with notifiers.
> 
> Prepare ground for this by adding a notifier list to the RCU reader
> struct and use it in wait_for_readers() if drain_rcu_call() is in
> progress. An API is added for readers to register their notifiers.
> 
> This is largely based on a draft from Paolo Bonzini.
> 
> Suggested-by: Paolo Bonzini<pbonzini@redhat.com>
> Signed-off-by: Greg Kurz<groug@kaod.org>
> ---
>   include/qemu/rcu.h | 15 +++++++++++++++
>   util/rcu.c         | 19 +++++++++++++++++++
>   2 files changed, 34 insertions(+)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~