Re: [LTP] mmstress[1309]: segfault at 7f3d71a36ee8 ip 00007f3d77132bdf sp 00007f3d71a36ee8 error 4 in libc-2.27.so[7f3d77058000+1aa000]

[Naresh Kamboju]

On Fri, 23 Oct 2020 at 22:03, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Fri, Oct 23, 2020 at 8:54 AM Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > On Fri, Oct 23, 2020 at 12:14 AM Rasmus Villemoes
> > <linux@xxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > That's certainly garbage. Now, I don't know if it's a sufficient fix (or
> > > could break something else), but the obvious first step of rearranging
> > > so that the ptr argument is evaluated before the assignment to __val_pu
> >
> > Ack. We could do that.
> >
> > I'm more inclined to just bite the bullet and go back to the ugly
> > conditional on the size that I had hoped to avoid, but if that turns
> > out too ugly, mind signing off on your patch and I'll have that as a
> > fallback?
>
> Actually, looking at that code, and the fact that we've used the
> "register asm()" format forever for the get_user() side, I think your
> approach is the right one.
>
> I'd rename the internal ptr variable to "__ptr_pu", and make sure the
> assignments happen just before the asm call (with the __val_pu
> assignment being the final thing).
>
> lso, it needs to be
>
>         void __user *__ptr_pu;
>
> instead of
>
>         __typeof__(ptr) __ptr = (ptr);
>
> because "ptr" may actually be an array, and we need to have the usual
> C "array to pointer" conversions happen, rather than try to make
> __ptr_pu be an array too.
>
> So the patch would become something like the appended instead, but I'd
> still like your sign-off (and I'd put you as author of the fix).
>
> Narest, can you confirm that this patch fixes the issue for you?

This patch fixed the reported problem.

Tested-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>

Build location:
https://builds.tuxbuild.com/uDAiW8jkN61oWoyxZDkEYA/

Test logs,
https://lkft.validation.linaro.org/scheduler/job/1868045#L1597

- Naresh