On Mon, 31 Oct 2022 11:43:30 -0700 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > Updated subject line, and here's the link to the original discussion > for new people: > > https://lore.kernel.org/all/B88D3073-440A-41C7-95F4-895D3F657EF2@xxxxxxxxx/ > > On Mon, Oct 31, 2022 at 10:28 AM Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > Ok. At that point we no longer have the pte or the virtual address, so > > it's not going to be exactly the same debug output. > > > > But I think it ends up being fairly natural to do > > > > VM_WARN_ON_ONCE_PAGE(page_mapcount(page) < 0, page); > > > > instead, and I've fixed that last patch up to do that. > > Ok, so I've got a fixed set of patches based on the feedback from > PeterZ, and also tried to do the s390 updates for this blindly, and > pushed them out into a git branch: > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/?h=mmu_gather-race-fix > > If people really want to see the patches in email again, I can do > that, but most of you already have, and the changes are either trivial > fixes or the s390 updates. > > For the s390 people that I've now added to the participant list maybe > the git tree is fine - and the fundamental explanation of the problem > is in that top-most commit (with the three preceding commits being > prep-work). Or that link to the thread about this all. > > That top-most commit is also where I tried to fix things up for s390 > that uses its own non-gathering TLB flush due to > CONFIG_MMU_GATHER_NO_GATHER. > > NOTE NOTE NOTE! Unlike my regular git branch, this one may end up > rebased etc for further comments and fixes. So don't consider that > stable, it's still more of an RFC branch. > > At a minimum I'll update it with Ack's etc, assuming I get those, and > my s390 changes are entirely untested and probably won't work. > > As far as I can tell, s390 doesn't actually *have* the problem that > causes this change, because of its synchronous TLB flush, but it > obviously needs to deal with the change of rmap zapping logic. Correct, we need to flush already when we change a PTE, which is done in ptep_get_and_clear() etc. Only exception would be lazy flushing when only one active thread is attached, then we would flush later in flush_tlb_mm/range(), or as soon as another thread is attached (IIRC). So it seems straight forward to just call page_zap_pte_rmap() from our private __tlb_remove_page_size() implementation. Just wondering a bit why you did not also add the VM_WARN_ON_ONCE_PAGE(page_mapcount(page) < 0, page), like in the generic change. Acked-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> # s390
