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Date: Thu, 13 Mar 2014 22:43:32 -0700 From: John Fastabend <john.fastabend@...il.com> To: paulmck@...ux.vnet.ibm.com CC: Eric Dumazet <eric.dumazet@...il.com>, xiyou.wangcong@...il.com, jhs@...atatu.com, netdev@...r.kernel.org, davem@...emloft.net Subject: Re: [RCU PATCH 06/14] net: sched: fw use RCU On 03/13/2014 02:15 PM, Paul E. McKenney wrote: > On Thu, Mar 13, 2014 at 01:56:43PM -0700, Eric Dumazet wrote: >> On Thu, 2014-03-13 at 13:22 -0700, Paul E. McKenney wrote: >> >>> Hmmm... You know, the offset that kfree uses is a byte offset. I see >>> no reason why any of the rcu_head structures should be misaligned. If >>> HTSIZE is too big by only a factor of four or smaller, would the following >>> (untested) patch to RCU be appropriate? >>> >>> Thanx, Paul >>> >>> ------------------------------------------------------------------------ >>> >>> rcu: Increase kfree_rcu() offset range >>> >>> The kfree_rcu() function operates by placing an offset into the rcu_head >>> structure in place of the function pointer that is normally there. >>> This offset cannot exceed 4095, on the theory that no Linux kernel will >>> ever have executable code in page zero. However, the rcu_head structure >>> contains a pair of function pointers, and should never be misaligned. >>> This commit therefore divides the offset by the size of a pointer when >>> being placed into the rcu_head structure, and multiplies it by this >>> same constant when pulling it out. >>> >>> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> >> >> SGTM, thanks Paul. >> >> Reviewed-by: Eric Dumazet <edumzzet@...gle.com> > > Very good, thank you! > > John, could you please give it a try with that rcu_head structure > moved to the end and let me know how it goes? > > Thanx, Paul > Yep, this resolves the BUILD_BUG_ON I was seeing previously. Thanks! Tested-by: John Fastabend <john.r.fastabend@...el.com> -- John Fastabend Intel Corporation -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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