Re: [Qemu-devel] [PATCH] rcu: actually register threads that have RCU read-side critical sections

[Wen Congyang <wency@cn.fujitsu.com>]

On 07/22/2015 10:18 PM, Paolo Bonzini wrote:
> Otherwise, grace periods are detected too early!

We always use qemu_thread_create() in qemu. So I think we can do it like this:
wrapped_fn()
{
    rcu_register_thread();
    call thread_fn() here
    rcu_unregister_thread();
}

So we will never forget to call rcu_register_thread() when creating a new thread.

Thanks
Wen Congyang

> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  cpus.c                | 6 ++++++
>  iothread.c            | 5 +++++
>  migration/migration.c | 4 ++++
>  tests/test-rcu-list.c | 4 ++++
>  util/rcu.c            | 2 ++
>  5 files changed, 21 insertions(+)
> 
> diff --git a/cpus.c b/cpus.c
> index b00a423..a822ce3 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -954,6 +954,8 @@ static void *qemu_kvm_cpu_thread_fn(void *arg)
>      CPUState *cpu = arg;
>      int r;
>  
> +    rcu_register_thread();
> +
>      qemu_mutex_lock_iothread();
>      qemu_thread_get_self(cpu->thread);
>      cpu->thread_id = qemu_get_thread_id();
> @@ -995,6 +997,8 @@ static void *qemu_dummy_cpu_thread_fn(void *arg)
>      sigset_t waitset;
>      int r;
>  
> +    rcu_register_thread();
> +
>      qemu_mutex_lock_iothread();
>      qemu_thread_get_self(cpu->thread);
>      cpu->thread_id = qemu_get_thread_id();
> @@ -1034,6 +1038,8 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
>  {
>      CPUState *cpu = arg;
>  
> +    rcu_register_thread();
> +
>      qemu_mutex_lock_iothread();
>      qemu_tcg_init_cpu_signals();
>      qemu_thread_get_self(cpu->thread);
> diff --git a/iothread.c b/iothread.c
> index 6d2a33f..da6ce7b 100644
> --- a/iothread.c
> +++ b/iothread.c
> @@ -18,6 +18,7 @@
>  #include "sysemu/iothread.h"
>  #include "qmp-commands.h"
>  #include "qemu/error-report.h"
> +#include "qemu/rcu.h"
>  
>  typedef ObjectClass IOThreadClass;
>  
> @@ -31,6 +32,8 @@ static void *iothread_run(void *opaque)
>      IOThread *iothread = opaque;
>      bool blocking;
>  
> +    rcu_register_thread();
> +
>      qemu_mutex_lock(&iothread->init_done_lock);
>      iothread->thread_id = qemu_get_thread_id();
>      qemu_cond_signal(&iothread->init_done_cond);
> @@ -45,6 +48,8 @@ static void *iothread_run(void *opaque)
>          }
>          aio_context_release(iothread->ctx);
>      }
> +
> +    rcu_unregister_thread();
>      return NULL;
>  }
>  
> diff --git a/migration/migration.c b/migration/migration.c
> index 86ca099..fd4f99b 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -22,6 +22,7 @@
>  #include "block/block.h"
>  #include "qapi/qmp/qerror.h"
>  #include "qemu/sockets.h"
> +#include "qemu/rcu.h"
>  #include "migration/block.h"
>  #include "qemu/thread.h"
>  #include "qmp-commands.h"
> @@ -917,6 +918,8 @@ static void *migration_thread(void *opaque)
>      int64_t start_time = initial_time;
>      bool old_vm_running = false;
>  
> +    rcu_register_thread();
> +
>      qemu_savevm_state_header(s->file);
>      qemu_savevm_state_begin(s->file, &s->params);
>  
> @@ -1016,6 +1019,7 @@ static void *migration_thread(void *opaque)
>      qemu_bh_schedule(s->cleanup_bh);
>      qemu_mutex_unlock_iothread();
>  
> +    rcu_unregister_thread();
>      return NULL;
>  }
>  
> diff --git a/tests/test-rcu-list.c b/tests/test-rcu-list.c
> index 4c5f62e..daa8bf4 100644
> --- a/tests/test-rcu-list.c
> +++ b/tests/test-rcu-list.c
> @@ -108,6 +108,8 @@ static void *rcu_q_reader(void *arg)
>      long long n_reads_local = 0;
>      struct list_element *el;
>  
> +    rcu_register_thread();
> +
>      *(struct rcu_reader_data **)arg = &rcu_reader;
>      atomic_inc(&nthreadsrunning);
>      while (goflag == GOFLAG_INIT) {
> @@ -129,6 +131,8 @@ static void *rcu_q_reader(void *arg)
>      qemu_mutex_lock(&counts_mutex);
>      n_reads += n_reads_local;
>      qemu_mutex_unlock(&counts_mutex);
> +
> +    rcu_unregister_thread();
>      return NULL;
>  }
>  
> diff --git a/util/rcu.c b/util/rcu.c
> index 7270151..cdcad67 100644
> --- a/util/rcu.c
> +++ b/util/rcu.c
> @@ -216,6 +216,8 @@ static void *call_rcu_thread(void *opaque)
>  {
>      struct rcu_head *node;
>  
> +    rcu_register_thread();
> +
>      for (;;) {
>          int tries = 0;
>          int n = atomic_read(&rcu_call_count);
>