Hi Heiko,
On Wednesday, 20 September 2017 05:15:17 PDT Heiko Carstens wrote:
> On Wed, Sep 20, 2017 at 08:51:00AM +0200, Martin Schwidefsky wrote:
> > Hi Paul,
> >
> > On Tue, 19 Sep 2017 22:07:57 -0700
> >
> > Paul Burton <paul.burton@xxxxxxxxxx> wrote:
> > > Commit c311c797998c ("cpumask: make "nr_cpumask_bits" unsigned")
> > > modified cpumsf_pmu_event_init() to cast the struct perf_event cpu field
> > > to an unsigned integer before it is compared with nr_cpumask_bits. This
> > > is broken because the cpu field may be -1 for events which follow a
> > > process rather than being affine to a particular CPU. When this is the
> > > case the cast to an unsigned int results in a value equal to ULONG_MAX,
> > > which is always greater than nr_cpumask_bits so we always fail
> > > cpumsf_pmu_event_init() and return -ENODEV.
> > >
> > > The check against nr_cpumask_bits seems nonsensical anyway, so this
> > > patch simply removes it. The cpu field is going to either be 0 or a
>
> I assume you meant to write "...either be -1..."?
Indeed I did... and I wrote -1 in the MIPS patch which I then copied this
from, so I'm not sure how it became 0. Oops!
> > > valid CPU number. Comparing it with nr_cpumask_bits is effectively
> > > checking that it's a valid cpu number, but it seems safe to rely on the
> > > core perf events code to ensure that's the case.
>
> Looks like you are right and the nr_cpumask_bits check is not needed. The
> sanity check is done at the beginning of perf_event_alloc() and everything
> else can rely on a sane cpu number (-1 or within bounds of nr_cpumask_bits).
> > Thanks for the patch, there is indeed an issue with nr_cpumask_bits.
> > But we already have a slightly different fix for this queued on the
> > fixes branch of s390/linux:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/commit/?h=f
> > ixes&id=fc3100d64f0ae383ae8d845989103da06d62763b
> So we should either use your patch or remove the superfluous check with an
> addon patch. Martin's call ;)
Glad the patch is of use either way.
Thanks,
PaulAttachment:
signature.asc
Description: This is a digitally signed message part.
