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, Paul
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