On Tue, 13 Aug 2019 16:31:35 -0700 (PDT) David Rientjes <rientjes@xxxxxxxxxx> wrote: > > > Move the debug checks to after verifying PageBuddy is true. This isolates > > > the scope of the checks to only be for buddy pages which are on the zone's > > > freelist which move_freepages_block() is operating on. In this case, an > > > incorrect node or zone is a bug worthy of being warned about (and the > > > examination of struct page is acceptable bcause this memory is not > > > reserved). > > > > I'm thinking Fixes:907ec5fca3dc and Cc:stable? But 907ec5fca3dc is > > almost a year old, so you were doing something special to trigger this? > > > > We noticed it almost immediately after bringing 907ec5fca3dc in on > CONFIG_DEBUG_VM builds. It depends on finding specific free pages in the > per-zone free area where the math in move_freepages() will bring the start > or end pfn into reserved memory and wanting to claim that entire pageblock > as a new migratetype. So the path will be rare, require CONFIG_DEBUG_VM, > and require fallback to a different migratetype. > > Some struct pages were already zeroed from reserve pages before > 907ec5fca3c so it theoretically could trigger before this commit. I think > it's rare enough under a config option that most people don't run that > others may not have noticed. I wouldn't argue against a stable tag and > the backport should be easy enough, but probably wouldn't single out a > commit that this is fixing. OK, thanks. I added the above two paragraphs to the changelog and removed the Fixes: Hopefully Mel will be able to review this for us.
