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    Subject[PATCH 4.4 142/268] perf/cgroup: Fix child event counting bug
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Song Liu <songliubraving@fb.com>

    [ Upstream commit c917e0f259908e75bd2a65877e25f9d90c22c848 ]

    When a perf_event is attached to parent cgroup, it should count events
    for all children cgroups:

    parent_group <---- perf_event
    \
    - child_group <---- process(es)

    However, in our tests, we found this perf_event cannot report reliable
    results. Here is an example case:

    # create cgroups
    mkdir -p /sys/fs/cgroup/p/c
    # start perf for parent group
    perf stat -e instructions -G "p"

    # on another console, run test process in child cgroup:
    stressapptest -s 2 -M 1000 & echo $! > /sys/fs/cgroup/p/c/cgroup.procs

    # after the test process is done, stop perf in the first console shows

    <not counted> instructions p

    The instruction should not be "not counted" as the process runs in the
    child cgroup.

    We found this is because perf_event->cgrp and cpuctx->cgrp are not
    identical, thus perf_event->cgrp are not updated properly.

    This patch fixes this by updating perf_cgroup properly for ancestor
    cgroup(s).

    Reported-by: Ephraim Park <ephiepark@fb.com>
    Signed-off-by: Song Liu <songliubraving@fb.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: <jolsa@redhat.com>
    Cc: <kernel-team@fb.com>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Link: http://lkml.kernel.org/r/20180312165943.1057894-1-songliubraving@fb.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    kernel/events/core.c | 21 ++++++++++++++++-----
    1 file changed, 16 insertions(+), 5 deletions(-)

    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -419,9 +419,15 @@ static inline void __update_cgrp_time(st

    static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context *cpuctx)
    {
    - struct perf_cgroup *cgrp_out = cpuctx->cgrp;
    - if (cgrp_out)
    - __update_cgrp_time(cgrp_out);
    + struct perf_cgroup *cgrp = cpuctx->cgrp;
    + struct cgroup_subsys_state *css;
    +
    + if (cgrp) {
    + for (css = &cgrp->css; css; css = css->parent) {
    + cgrp = container_of(css, struct perf_cgroup, css);
    + __update_cgrp_time(cgrp);
    + }
    + }
    }

    static inline void update_cgrp_time_from_event(struct perf_event *event)
    @@ -449,6 +455,7 @@ perf_cgroup_set_timestamp(struct task_st
    {
    struct perf_cgroup *cgrp;
    struct perf_cgroup_info *info;
    + struct cgroup_subsys_state *css;

    /*
    * ctx->lock held by caller
    @@ -459,8 +466,12 @@ perf_cgroup_set_timestamp(struct task_st
    return;

    cgrp = perf_cgroup_from_task(task, ctx);
    - info = this_cpu_ptr(cgrp->info);
    - info->timestamp = ctx->timestamp;
    +
    + for (css = &cgrp->css; css; css = css->parent) {
    + cgrp = container_of(css, struct perf_cgroup, css);
    + info = this_cpu_ptr(cgrp->info);
    + info->timestamp = ctx->timestamp;
    + }
    }

    #define PERF_CGROUP_SWOUT 0x1 /* cgroup switch out every event */

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