Messages in this thread | | | Date | Sat, 3 Jan 2009 15:46:37 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [RFC, PATCH] kernel/rcu: add kfree_rcu |
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On Sat, Jan 03, 2009 at 03:59:40PM +0100, Manfred Spraul wrote: > Paul E. McKenney wrote: >> I would suggest instead using the bottom bit to differentiate between >> these two cases, especially given that your approach makes it impossible >> for callback processing to notice a NULL function pointer. In addition, >> this approach would allow different types of allocators to be specified >> should this later prove to be helpful. You should not have to shift the >> offset because the rcu_head offset should always be a multiple of four >> (or eight on 64-bit architectures). >> > We must be careful: rcu_head might be always aligned, but are function > pointers always aligned? > The x86 hardware allows arbitrary function pointers, I'm not sure what gcc > would do if '--falign-functions=0' is used. > Are there other codepaths that assume that the lowest bit of a function > pointer is never set?
Good point. I guess that we will have to worry about expandability when and if the need arises. I see a couple of ways of doing it, but they are pretty ugly...
>> And we really are running into bugs that are detected by RCU's seeing a >> null function pointer in the rcu_head structure at callback-invocation >> time. So, whatever encoding you choose, please leave a function-pointer >> value of zero as an invalid value! >> > Ok. > >>> --- a/kernel/rcutree.c >>> +++ b/kernel/rcutree.c >>> @@ -901,7 +901,7 @@ static void rcu_do_batch(struct rcu_data *rdp) >>> while (list) { >>> next = list->next; >>> prefetch(next); >>> - list->func(list); >>> + rcu_docallback(list); >>> >> >> Good, you got all three of them! ;-) >> >> > The patch was tested against rcutree ;-)
;-)
Thanx, Paul
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