Re: [Qemu-devel] [PATCH v3 2/4] exec: Protect map_client_list with mutex

[Fam Zheng <famz@redhat.com>]

On Mon, 03/16 08:33, Paolo Bonzini wrote:
> 
> 
> On 16/03/2015 06:31, Fam Zheng wrote:
> > So that accesses from multiple threads are safe.
> > 
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> > ---
> >  exec.c | 24 +++++++++++++++---------
> >  1 file changed, 15 insertions(+), 9 deletions(-)
> > 
> > diff --git a/exec.c b/exec.c
> > index 4080044..3e54580 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -429,15 +429,6 @@ address_space_translate_for_iotlb(CPUState *cpu, hwaddr addr,
> >  }
> >  #endif
> >  
> > -void cpu_exec_init_all(void)
> > -{
> > -#if !defined(CONFIG_USER_ONLY)
> > -    qemu_mutex_init(&ram_list.mutex);
> > -    memory_map_init();
> > -    io_mem_init();
> > -#endif
> > -}
> > -
> >  #if !defined(CONFIG_USER_ONLY)
> >  
> >  static int cpu_common_post_load(void *opaque, int version_id)
> > @@ -2494,6 +2485,7 @@ typedef struct MapClient {
> >      QLIST_ENTRY(MapClient) link;
> >  } MapClient;
> >  
> > +QemuMutex map_client_list_lock;
> >  static QLIST_HEAD(map_client_list, MapClient) map_client_list
> >      = QLIST_HEAD_INITIALIZER(map_client_list);
> >  
> > @@ -2501,12 +2493,24 @@ void *cpu_register_map_client(void *opaque, void (*callback)(void *opaque))
> >  {
> >      MapClient *client = g_malloc(sizeof(*client));
> >  
> > +    qemu_mutex_lock(&map_client_list_lock);
> >      client->opaque = opaque;
> >      client->callback = callback;
> >      QLIST_INSERT_HEAD(&map_client_list, client, link);
> > +    qemu_mutex_unlock(&map_client_list_lock);
> >      return client;
> >  }
> >  
> > +void cpu_exec_init_all(void)
> > +{
> > +#if !defined(CONFIG_USER_ONLY)
> > +    qemu_mutex_init(&ram_list.mutex);
> > +    memory_map_init();
> > +    io_mem_init();
> > +#endif
> > +    qemu_mutex_init(&map_client_list_lock);
> > +}
> > +
> 
> You are moving cpu_exec_init_all within an #ifndef CONFIG_USER_ONLY.
> Does this patch compile for user-mode emulation?

No. Good catch!

> 
> The move itself is okay but only if you remove the two calls in
> *-user/main.c (and possibly move the prototype to include/exec/exec-all.h).

Sounds good, I'll split that patch in v4.

Fam

> 
> >  static void cpu_unregister_map_client(void *_client)
> >  {
> >      MapClient *client = (MapClient *)_client;
> > @@ -2519,11 +2523,13 @@ static void cpu_notify_map_clients(void)
> >  {
> >      MapClient *client;
> >  
> > +    qemu_mutex_lock(&map_client_list_lock);
> >      while (!QLIST_EMPTY(&map_client_list)) {
> >          client = QLIST_FIRST(&map_client_list);
> >          client->callback(client->opaque);
> 
> A good rule of thumb is never hold a lock while calling "unknown" code.
>  This will be fixed in patch 4, so it's okay.
> 
> Paolo
> 
> >          cpu_unregister_map_client(client);
> >      }
> > +    qemu_mutex_unlock(&map_client_list_lock);
> >  }
> >  
> >  bool address_space_access_valid(AddressSpace *as, hwaddr addr, int len, bool is_write)
> >