Commit 5626f8c6 authored by Dr. David Alan Gilbert's avatar Dr. David Alan Gilbert
Browse files

rcu: Add automatically released rcu_read_lock variants 

RCU_READ_LOCK_GUARD() takes the rcu_read_lock and then uses glib's
g_auto infrastructure (and thus whatever the compiler's hooks are) to
release it on all exits of the block.

WITH_RCU_READ_LOCK_GUARD() is similar but is used as a wrapper for the
lock, i.e.:

   WITH_RCU_READ_LOCK_GUARD() {
       stuff under lock
   }

Note the 'unused' attribute is needed to work around clang bug:
  https://bugs.llvm.org/show_bug.cgi?id=43482



Signed-off-by: default avatarDr. David Alan Gilbert <dgilbert@redhat.com>
Acked-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: default avatarDaniel P. Berrangé <berrange@redhat.com>
Message-Id: <20191007143642.301445-2-dgilbert@redhat.com>
Signed-off-by: default avatarDr. David Alan Gilbert <dgilbert@redhat.com>
parent 8f8d528e

docs/devel/rcu.txt

+16 −0
Original line number Diff line number Diff line
@@ -187,6 +187,22 @@ The following APIs must be used before RCU is used in a thread: 
Note that these APIs are relatively heavyweight, and should _not_ be

nested.



Convenience macros

==================



Two macros are provided that automatically release the read lock at the

end of the scope.



      RCU_READ_LOCK_GUARD()



         Takes the lock and will release it at the end of the block it's

         used in.



      WITH_RCU_READ_LOCK_GUARD()  { code }



         Is used at the head of a block to protect the code within the block.



Note that 'goto'ing out of the guarded block will also drop the lock.



DIFFERENCES WITH LINUX

======================

include/qemu/rcu.h

+25 −0
Original line number Diff line number Diff line
@@ -154,6 +154,31 @@ extern void call_rcu1(struct rcu_head *head, RCUCBFunc *func); 
      }),                                                                \

      (RCUCBFunc *)g_free);



typedef void RCUReadAuto;

static inline RCUReadAuto *rcu_read_auto_lock(void)

{

    rcu_read_lock();

    /* Anything non-NULL causes the cleanup function to be called */

    return (void *)(uintptr_t)0x1;

}



static inline void rcu_read_auto_unlock(RCUReadAuto *r)

{

    rcu_read_unlock();

}



G_DEFINE_AUTOPTR_CLEANUP_FUNC(RCUReadAuto, rcu_read_auto_unlock)



#define WITH_RCU_READ_LOCK_GUARD() \

    WITH_RCU_READ_LOCK_GUARD_(_rcu_read_auto##__COUNTER__)



#define WITH_RCU_READ_LOCK_GUARD_(var) \

    for (g_autoptr(RCUReadAuto) var = rcu_read_auto_lock(); \

        (var); rcu_read_auto_unlock(var), (var) = NULL)



#define RCU_READ_LOCK_GUARD() \

    g_autoptr(RCUReadAuto) _rcu_read_auto __attribute__((unused)) = rcu_read_auto_lock()



#ifdef __cplusplus

}

#endif