Re: [PATCH v2 1/1] selftests/proc: use RSS in /proc/pid/smaps_rollup tearing tests

[Suren Baghdasaryan]

On Mon, Nov 2, 2026 at 8:11 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
>
> On Mon, Nov 2, 2026 at 8:01 AM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > On Mon, 2 Nov 2026 07:43:17 -0800 Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
> >
> > > > :
> > > > : The patched userspace test passed all six cases on an existing
> > > > : x86-64 6.18.57 kernel, with a PID-namespace adjustment. That kernel
> > > > : predates ca5480fb53fa, so this checks selftest behavior, not the
> > > > : intended kernel's procfs changes. Separate syscall tests on that
> > > > : kernel confirmed the EXEC-merging and memlock failure cases.
> > >
> > > I'm guessing your bot was using personality() to make the tests fail.
> > > Again, I'm not sure we should handle such use case. Should we?
> >
> >
> > : The concern is pre-ARMv6 CPUs, where READ_IMPLIES_EXEC is set by
> > : default. Nobody needs to call personality() to encounter this there.
> > :
> > : We already addressed this in 0685630fdccb ("selftests/proc: make
> > : proc-maps-race work with READ_IMPLIES_EXEC"):
> > :
> > : https://lore.kernel.org/r/20260808200312.6326-1-kmehltretter@xxxxxxxxx
> > :
> > : That fixed split_vma(). Alternating PROT_EXEC in setup introduces the
> > : same assumption elsewhere: RW and RWX both become RWX, allowing adjacent
> > : mappings to merge. The parent then cannot find the expected three-page
> > : VMAs and the test fails during setup, before testing procfs tearing.
> > :
> > : Yes, the focused x86-64 check explicitly enabled READ_IMPLIES_EXEC to
> > : exercise this behavior. It wasn't tested on old ARM hardware. But I
> > : think we should preserve the existing support for those machines.
> > : Populating writable, then removing write permission from alternate
> > : mappings, preserves both RSS and the required VMA boundaries.
>
> Ah, I see now why handling READ_IMPLIES_EXEC is needed. Then your
> complete fix looks fine. Perhaps we should mention this pre-ARMv6 CPU
> detail in the changelog of your fix to explain why READ_IMPLIES_EXEC
> is important here?

I guess I have to ask whether you want to post your fix as a followup
to mine or if I should fold them into one patch and post a v3. What's
your preference?

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