Re: [PATCH 2/2] MIPS/c-r4k: do no use mmap_sem for gup_fast()

[Davidlohr Bueso]

On Thu, 07 Feb 2019, Paul Burton wrote:

> Hi Davidlohr,
>
> On Wed, Feb 06, 2019 at 09:37:40PM -0800, Davidlohr Bueso wrote:
> > It is well known that because the mm can internally
> > call the regular gup_unlocked if the lockless approach
> > fails and take the sem there, the caller must not hold
> > the mmap_sem already.
> >
> > Fixes: e523f289fe4d (MIPS: c-r4k: Fix sigtramp SMP call to use kmap)
> > Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> > Cc: Paul Burton <paul.burton@xxxxxxxx>
> > Cc: James Hogan <jhogan@xxxxxxxxxx>
> > Cc: linux-mips@xxxxxxxxxxxxxxx
> > Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
>
> Thanks - this looks good, but:
>
> 1) The problem it fixes was introduced in v4.8.
>
> 2) Commit adcc81f148d7 ("MIPS: math-emu: Write-protect delay slot
>    emulation pages") actually left flush_cache_sigtramp unused, and has
>    been backported to stable kernels also as far as v4.8.
>
> Therefore this will just fix code that never gets called, and I'll go
> delete the whole thing instead.

Even better.

Thanks,
Davidlohr