Re: [Qemu-devel] [RFC PATCH] convert ram_list to RCU DQ

[Paolo Bonzini]

Il 29/08/2013 21:18, Mike Day ha scritto:
> 
>> Similarly, here the critical section includes the caller, and block is
>> living across calls to host.  Again, for now just put all of ram_load
>> under a huge RCU critical section.  Later we can use ram_list.version to
>> refresh the list and make the critical sections smaller.
> 
> And: rcu_read_lock() and rcu_read_unlock() can be called recursively, so
> I can still leave the lock/unlock pair in host_from_stream_offset. 

I'm not sure about that; returning an RCU-protected variable after
rcu_read_unlock() seems wrong to me because the pointer may not be valid
at that point.  I suggest using a comment that asks to call
host_from_stream_offset within rcu_read_lock()/rcu_read_unlock().
However, if existing practice in the kernel is different, I'll bow to that.

Paolo