Re: x86/mm: Finishing off the fix for a should_flush_tlb race

[Greg Thelen]

On Tue, Feb 24, 2026 at 1:45 AM Stephen Dolan <sdolan@xxxxxxxxxxxxxx> wrote:
>
> On Wed, 18 Feb 2026 at 19:43, Seth Forshee <sforshee@xxxxxxxxxx> wrote:
> >
> > On Tue, Feb 17, 2026 at 05:21:19PM +0000, Stephen Dolan wrote:
> > > On Tue, 17 Feb 2026 at 15:20, Seth Forshee <sforshee@xxxxxxxxxx> wrote:
> > > > > I wanted to check on the status of the stable patches, since I see the
> > > > > upstream fix went into 6.18 but there's still no fix in the 6.12 stable
> > > > > tree. We've been seeing segfaults during a test case with 6.12, and
> > > > > after bisecting we found that reverting both "x86/mm: Eliminate window
> > > > > where TLB flushes may be inadvertently skipped" and "x86/mm/tlb: Only
> > > > > trim the mm_cpumask once a second" seems to get rid of the segfaults.
> > > > > I'll try to get some testing with the proposed stable patch today.
> > >
> > > Hmm, ok. I posted the patch to stable@xxxxxxxxxxxxxxx a while ago but
> > > it looks like it never got merged. Does this patch fix the issue for
> > > you?
> > >
> > >     https://lore.kernel.org/stable/CAHDw0oE0334gEJ=ga1PAnZ3Av8+tFkKF-MJCF7Jj3i6pBVJvFQ@xxxxxxxxxxxxxx/
> >
> > Without the patch we've seen a segfault within a couple of hours of
> > running our test case, often within 30 minutes. We ran for 18 hours
> > with the patch applied without any crashes, so it looks like it fixes
> > our crash.
> >
> > Thanks,
> > Seth
>
> That matches our testing also. I would still like to get this patch
> merged into the 6.1, 6.6 and 6.12 kernel trees to fix this tricky bug.
> But I'm pretty unfamiliar with the kernel development process and not
> sure how to get that done.
>
> Stephen
>

We're also seeing some 6.6 and 6.12 based test failures fixed by this patch.
Are there any objections to landing this change into stable (especially 6.6
and 6.12)?