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

[Paolo Bonzini]

On 23/07/2015 12:30, Christian Borntraeger wrote:
> Am 22.07.2015 um 16:18 schrieb Paolo Bonzini:
>> Otherwise, grace periods are detected too early!
> 
> I guess this or Wens proposal is still necessary for 2.4?

Yes.  I think this is better for 2.4.  There are threads that do not
need RCU, for example the thread-pool.c worker threads, so it may just
be simpler to add an assertion in rcu_register_thread.  I'm just a bit
wary of doing little more than the bare minimum in 2.4, because of the
OS X failure that I didn't quite understand.

Paolo

> 
>>
>> Signed-off-by: Paolo Bonzini <address@hidden>
>> ---
>>  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);
>>
> 
> 
>