Hi Oliver, On Friday 15 Apr 2022 at 21:58:53 (+0000), Oliver Upton wrote: > Breaking a table pte is insufficient to guarantee ownership of an > unlinked subtree. Parallel software walkers could be traversing > substructures and changing their mappings. > > Recurse through the unlinked subtree and lock all descendent ptes > to take ownership of the subtree. Since the ptes are actually being > evicted, return table ptes back to the table walker to ensure child > tables are also traversed. Note that this is done both in both the > pre-order and leaf visitors as the underlying pte remains volatile until > it is unlinked. Still trying to get the full picture of the series so bear with me. IIUC the case you're dealing with here is when we're coallescing a table into a block with concurrent walkers making changes in the sub-tree. I believe this should happen when turning dirty logging off? Why do we need to recursively lock the entire sub-tree at all in this case? As long as the table is turned into a locked invalid PTE, what concurrent walkers are doing in the sub-tree should be irrelevant no? None of the changes they do will be made visible to the hardware anyway. So as long as the sub-tree isn't freed under their feet (which should be the point of the RCU protection) this should be all fine? Is there a case where this is not actually true? Thanks, Quentin
