Messages in this thread | | | Date | Wed, 2 Nov 2022 10:14:42 +0100 | Subject | Re: mm: delay rmap removal until after TLB flush | From | Christian Borntraeger <> |
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Am 31.10.22 um 19:43 schrieb Linus Torvalds: > 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@gmail.com/ > > On Mon, Oct 31, 2022 at 10:28 AM Linus Torvalds > <torvalds@linux-foundation.org> 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.
Adding Gerald.
> > 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. > > Also added a few people who are explicitly listed as being mmu_gather > maintainers. Maybe people saw the discussion on the linux-mm list, but > let's make it explicit. > > Do people have any objections to this approach, or other suggestions? > > I do *not* consider this critical, so it's a "queue for 6.2" issue for me. > > It probably makes most sense to queue in the -MM tree (after the thing > is acked and people agree), but I can keep that branch alive too and > just deal with it all myself as well. > > Anybody? > > Linus
It certainly needs a build fix for s390:
In file included from kernel/sched/core.c:78: ./arch/s390/include/asm/tlb.h: In function '__tlb_remove_page_size': ./arch/s390/include/asm/tlb.h:50:17: error: implicit declaration of function 'page_zap_pte_rmap' [-Werror=implicit-function-declaration] 50 | page_zap_pte_rmap(page); | ^~~~~~~~~~~~~~~~~
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