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    Subject[PATCH 2/2] perf evsel: Fix inverted test for fixing up attr.inherit flag
    Date
    From: Arnaldo Carvalho de Melo <acme@redhat.com>

    The kernel refuses mmapping an event with the inherit flag set for
    something that is systemwide (cpu == -1), and the evsel layer got this
    reversed at some point, fix it.

    The symtom was that the --pid and --tid parameters for 'perf record' and
    'perf top' returned with -EINVAL, like:

    # /tmp/build-perf/perf record -v -fo/tmp/perf.data -p 1042
    Warning: ... trying to fall back to cpu-clock-ticks

    Fatal: failed to mmap with 22 (Invalid argument)

    Reported-by: David Ahern <dsahern@gmail.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Mike Galbraith <efault@gmx.de>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Tom Zanussi <tzanussi@gmail.com>
    LKML-Reference: <new-submission>
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    ---
    tools/perf/util/evsel.c | 15 +++++++++++++--
    1 files changed, 13 insertions(+), 2 deletions(-)

    diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
    index 63cadaf..8083d51 100644
    --- a/tools/perf/util/evsel.c
    +++ b/tools/perf/util/evsel.c
    @@ -179,8 +179,19 @@ static int __perf_evsel__open(struct perf_evsel *evsel, struct cpu_map *cpus,

    for (cpu = 0; cpu < cpus->nr; cpu++) {
    int group_fd = -1;
    -
    - evsel->attr.inherit = (cpus->map[cpu] < 0) && inherit;
    + /*
    + * Don't allow mmap() of inherited per-task counters. This
    + * would create a performance issue due to all children writing
    + * to the same buffer.
    + *
    + * FIXME:
    + * Proper fix is not to pass 'inherit' to perf_evsel__open*,
    + * but a 'flags' parameter, with 'group' folded there as well,
    + * then introduce a PERF_O_{MMAP,GROUP,INHERIT} enum, and if
    + * O_MMAP is set, emit a warning if cpu < 0 and O_INHERIT is
    + * set. Lets go for the minimal fix first tho.
    + */
    + evsel->attr.inherit = (cpus->map[cpu] >= 0) && inherit;

    for (thread = 0; thread < threads->nr; thread++) {

    --
    1.6.2.5


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