Messages in this thread | | | Date | Sun, 12 Feb 2012 09:41:33 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] x86, mce: Fix rcu splat in drain_mce_log_buffer() |
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On Mon, Feb 06, 2012 at 05:18:02PM +0100, Borislav Petkov wrote: > On Fri, Jan 13, 2012 at 01:44:35PM -0800, Paul E. McKenney wrote: > > Looks good to me, but I do need to defer to people who know this code > > better than do I. The key thing that (from what I can see) makes > > rcu_dereference() unnecessary is that the smp_rmb() used in conjunction > > with polling the .finished field takes care of ordering. > > Right, this was me trying hard not to screw up touching mcelog.next, > thus trying to use the rcu_dereference_index_check() primitive without > thinking it through too much. But you're right, I'm polling the > ->finished field 4 times (totally arbitrary, btw) which should suffice > while the mce_log() routine above writes those entries. > > Although, the question still remains, since mce_log() accesses > mcelog.next through the rcu_dereference_index_check() primitive, > shouldn't I do it the same way?
I don't claim to be an mce_log() expert, but when I looked it over, I didn't see a need for rcu_dereference_index_check(). Unless I am confused (quite possible), the memory barriers are sufficient.
The rcu_read_lock() and rcu_read_unlock() seem to be needed to avoid premature freeing, though.
Thanx, Paul
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