Re: [Qemu-devel] [PATCH 03/15] rcu: allow nesting of rcu_read_lock/rcu_read_unlock

[Fam Zheng <famz@redhat.com>]

On Thu, 01/22 15:47, Paolo Bonzini wrote:
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  include/qemu/rcu.h | 15 ++++++++++++++-
>  tests/rcutorture.c |  2 ++
>  2 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h
> index cfef36e..da043f2 100644
> --- a/include/qemu/rcu.h
> +++ b/include/qemu/rcu.h
> @@ -68,6 +68,9 @@ struct rcu_reader_data {
>      unsigned long ctr;
>      bool waiting;
>  
> +    /* Data used by reader only */
> +    unsigned depth;
> +
>      /* Data used for registry, protected by rcu_gp_lock */
>      QLIST_ENTRY(rcu_reader_data) node;
>  };
> @@ -77,8 +80,13 @@ extern __thread struct rcu_reader_data rcu_reader;
>  static inline void rcu_read_lock(void)
>  {
>      struct rcu_reader_data *p_rcu_reader = &rcu_reader;
> +    unsigned ctr;
> +
> +    if (p_rcu_reader->depth++ > 0) {
> +        return;
> +    }
>  
> -    unsigned ctr = atomic_read(&rcu_gp_ctr);
> +    ctr = atomic_read(&rcu_gp_ctr);
>      atomic_xchg(&p_rcu_reader->ctr, ctr);
>      if (atomic_read(&p_rcu_reader->waiting)) {
>          atomic_set(&p_rcu_reader->waiting, false);
> @@ -90,6 +98,11 @@ static inline void rcu_read_unlock(void)
>  {
>      struct rcu_reader_data *p_rcu_reader = &rcu_reader;
>  
> +    assert(p_rcu_reader->depth != 0);
> +    if (--p_rcu_reader->depth > 0) {
> +        return;
> +    }
> +
>      atomic_xchg(&p_rcu_reader->ctr, 0);
>      if (atomic_read(&p_rcu_reader->waiting)) {
>          atomic_set(&p_rcu_reader->waiting, false);
> diff --git a/tests/rcutorture.c b/tests/rcutorture.c
> index 214985f..31461c3 100644
> --- a/tests/rcutorture.c
> +++ b/tests/rcutorture.c
> @@ -257,9 +257,11 @@ static void *rcu_read_stress_test(void *arg)
>          if (p->mbtest == 0) {
>              n_mberror++;
>          }
> +        rcu_read_lock();
>          for (i = 0; i < 100; i++) {
>              garbage++;
>          }
> +        rcu_read_unlock();
>          pc = p->pipe_count;
>          rcu_read_unlock();
>          if ((pc > RCU_STRESS_PIPE_LEN) || (pc < 0)) {
> -- 
> 1.8.3.1
> 
> 

Reviewed-by: Fam Zheng <famz@redhat.com>