Messages in this thread | | | Date | Wed, 25 Aug 2021 14:29:19 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] rbtree: stop iteration early in rb_find_first |
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On Wed, Aug 25, 2021 at 04:53:32AM -0700, Michel Lespinasse wrote: > On Wed, Aug 25, 2021 at 01:39:26PM +0200, Peter Zijlstra wrote: > > On Wed, Aug 25, 2021 at 05:59:48PM +0800, Li RongQing wrote: > > > stop iteration if match is not NULL and result of cmp is > > > not zero, this means the matched node has been found, and > > > the node with same key has been passed > > > > > > Signed-off-by: Li RongQing <lirongqing@baidu.com> > > > --- > > > include/linux/rbtree.h | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h > > > index d31ecaf4fdd3..2689771df9bb 100644 > > > --- a/include/linux/rbtree.h > > > +++ b/include/linux/rbtree.h > > > @@ -324,6 +324,9 @@ rb_find_first(const void *key, const struct rb_root *tree, > > > } else if (c > 0) { > > > node = node->rb_right; > > > } > > > + > > > + if (match && c) > > > + break; > > > } > > > > > > return match; > > > > Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> > > NAK. This looked slightly wrong before, and is more wrong after. > > Before: > there was this weird condition if (c <= 0) {} else if (c > 0) {} , > making you wonder what the third possibility may be. Easy fix would be > to remove the second condition. > > After: > say the key is equal the root, so the code sets match=root and goes left. > Then it stops searching because match is set and c<0. > This doesn't work, the code needs to keep searching for the leftmost match.
I'm not following you. If c!=0 the key didn't match. If c<0 the key is less than the one we're looking for, meaning we've already found the left-most matching key, idem for c>0.
More specifically, can you draw me a (binary) tree with elements: A B B B C, such that a search for B might have match set, hit c!=1 and not have found the leftmost B ?
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