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 V6xWBNp+ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: * Andrew Morton [241101 09:54]: > On Thu, 31 Oct 2024 23:16:22 +0000 Wei Yang wrote: > > > The original thread[1] thoughts it is a problem in mas_new_root(). But after > > discussion, this should be an improvement on storing NULL. > > I hate to be a bureaucrat, but that isn't a very satisfying [0/N]. > > > > > [1]: https://lkml.kernel.org/r/20241015233909.23592-1-richard.weiyang@gmail.com > > From here I extracted "When overwriting the whole range with NULL, > current behavior is not correct", but that's still very thin. What is > incorrect about it and what is the impact of all of this to Linux users? > An empty tree is represented by having the tree point to NULL directly. An empty tree indicates the entire range (0-ULONG_MAX) is NULL. A store operation into an existing node that causes 0 - ULONG_MAX to be equal to NULL may not be restored to an empty state - a node is used to store the single range instead. This is wasteful and different from the initial setup of the tree. Once the tree is using a single node to store 0 - ULONG_MAX, problems may arise when storing more values into a tree with the unexpected state of 0 - ULONG being a single range in a node. User visible issues may mean a corrupt tree and incorrect storage of information within the tree. This would be limited to users who create and then empty a tree by overwriting all values, then try to store more NULLs into the empty tree. I cannot come up with an example of any user doing this (users usually destroy the tree and generally don't keep trying to store NULLs over NULLs), but patch 4/5 "maple_tree: refine mas_store_root() on storing NULL" should be backported just in case. I said patch 4/5 needed to be backported in v3 [1], but stable didn't get added to the Cc list and I missed it on review of v4. I added to the confusion by stating in an earlier version that it did not need to be backported [2]. At the time the issue of corrupting the node wasn't in the description. It should go back to v6.1. I will be more clear in my communication on Cc'ing stable in the future. The description of 4/5 is inadequate and I'll respond there as well. [1] https://lore.kernel.org/all/jo4wjti235pqmzd6qaziexzjsavt53vmtyzyvw4htrcwpuxf4n@ctyucxk5avrc/ [2] https://lore.kernel.org/all/ia7qdjv5c5hmg6yds3tz2x5to5u65k47ssgudiayxjqrowu4fm@i5la2j7kpe5k/ Thanks, Liam