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 qAQtTsFV 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newer kernel (after the > > > "Avoid zeroing vma tree in mmap_region()" patch and before the fix). > > > My original goal was to trigger the bug on older kernels, > > > but that does not work, yet. > > > > > > Bert Karwatzki > > > > Thanks, that's great! > > > > For older kernels the problem should still be present, the fundamental > > thing that changed from the point of view of this bug is that merge won't > > contribute to the number of VMAs being overwritten at once. > > > > To trigger prior to commit f8d112a4e657 ("mm/mmap: avoid zeroing vma tree > > in mmap_region()") you would need to create a situation where the _clear_ > > triggers the bug, i.e. you must consistute all the VMAs that are being > > overwritten by the store from existing VMAs you are overwriting with a > > MAP_FIXED. > > > > So some tweaks should get you there... > > > > > I don't think triggering the bug on a clear works, because a write of a %NULL > that will cause a node to end with a %NULL becomes a spanning write into the > next node: > > /* > * mas_is_span_wr() - Check if the write needs to be treated as a write that > * spans the node. > * @mas: The maple state > * @piv: The pivot value being written > * @type: The maple node type > * @entry: The data to write > * > * Spanning writes are writes that start in one node and end in another OR if > * the write of a %NULL will cause the node to end with a %NULL. > * > * Return: True if this is a spanning write, false otherwise. > */ > static bool mas_is_span_wr(struct ma_wr_state *wr_mas) > { > > > I think the could would trigger in this situation > > Node_0 > / > / > Node_1 > / \ > / \ > Node_2 Node_3 > > but only if Node_3 contained only two ranges, one empty range and one normal > range, and if the mmap into empty range of Node_3 would merge with the last > range of Node_2 and the last range of Node_3. But I think the rebalancing of the > tree will make it very hard if not impossible to create such a node. > > > Bert Karwatzki Hm well that would explain why we couldn't hit it so easy in the past then, and is a good thing... :) Still the bug is still a bug even if hard to hit from mm code and should get backported (obviously you're suggesting otherwise, just to emphasise :)