On Sun, May 06 2018, Herbert Xu wrote: > On Sun, May 06, 2018 at 07:48:20AM +1000, NeilBrown wrote: >> >> The spinlock protects 2 or more buckets. The nested table contains at >> least 512 buckets, maybe more. >> It is quite possible for two insertions into 2 different buckets to both >> get their spinlock and both try to instantiate the same nested table. > > I think you missed the fact that when we use nested tables the spin > lock table is limited to just a single page and hence corresponds > to the first level in the nested table. Therefore it's always safe.
Yes I had missed that - thanks for pointing it out. In fact the lock table is limited to the number of nested_tables in the second level. And it is the same low-order bits that choose both the lock and the set of nested tables. So there isn't a bug here. So we don't need this patch. (I still like it though - it seems more obviously correct). Thanks, NeilBrown
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