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Date: Fri, 30 Aug 2013 10:19:16 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC PATCH] convert ram_list to RCU DQ
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To: Mike Day <ncmike@ncultra.org>
Cc: Paul Mckenney <paulmck@linux.vnet.ibm.com>, Mathew Desnoyers <mathieu.desnoyers@efficios.com>, qemu-devel@nongnu.org, Anthony Liguori <anthony@codemonkey.ws>

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