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    Subject[PATCH 4.14 423/496] perf/core: Fix installing cgroup events on CPU
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: "leilei.lin" <leilei.lin@alibaba-inc.com>

    [ Upstream commit 33801b94741d6c3be9713c10aa627477216c21e2 ]

    There's two problems when installing cgroup events on CPUs: firstly
    list_update_cgroup_event() only tries to set cpuctx->cgrp for the
    first event, if that mismatches on @cgrp we'll not try again for later
    additions.

    Secondly, when we install a cgroup event into an active context, only
    issue an event reprogram when the event matches the current cgroup
    context. This avoids a pointless event reprogramming.

    Signed-off-by: leilei.lin <leilei.lin@alibaba-inc.com>
    [ Improved the changelog and comments. ]
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    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: Stephane Eranian <eranian@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Cc: brendan.d.gregg@gmail.com
    Cc: eranian@gmail.com
    Cc: linux-kernel@vger.kernel.org
    Cc: yang_oliver@hotmail.com
    Link: http://lkml.kernel.org/r/20180306093637.28247-1-linxiulei@gmail.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 | 46 +++++++++++++++++++++++++++++++++++-----------
    1 file changed, 35 insertions(+), 11 deletions(-)

    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -900,27 +900,39 @@ list_update_cgroup_event(struct perf_eve
    if (!is_cgroup_event(event))
    return;

    - if (add && ctx->nr_cgroups++)
    - return;
    - else if (!add && --ctx->nr_cgroups)
    - return;
    /*
    * Because cgroup events are always per-cpu events,
    * this will always be called from the right CPU.
    */
    cpuctx = __get_cpu_context(ctx);
    - cpuctx_entry = &cpuctx->cgrp_cpuctx_entry;
    - /* cpuctx->cgrp is NULL unless a cgroup event is active in this CPU .*/
    - if (add) {
    +
    + /*
    + * Since setting cpuctx->cgrp is conditional on the current @cgrp
    + * matching the event's cgroup, we must do this for every new event,
    + * because if the first would mismatch, the second would not try again
    + * and we would leave cpuctx->cgrp unset.
    + */
    + if (add && !cpuctx->cgrp) {
    struct perf_cgroup *cgrp = perf_cgroup_from_task(current, ctx);

    - list_add(cpuctx_entry, this_cpu_ptr(&cgrp_cpuctx_list));
    if (cgroup_is_descendant(cgrp->css.cgroup, event->cgrp->css.cgroup))
    cpuctx->cgrp = cgrp;
    - } else {
    - list_del(cpuctx_entry);
    - cpuctx->cgrp = NULL;
    }
    +
    + if (add && ctx->nr_cgroups++)
    + return;
    + else if (!add && --ctx->nr_cgroups)
    + return;
    +
    + /* no cgroup running */
    + if (!add)
    + cpuctx->cgrp = NULL;
    +
    + cpuctx_entry = &cpuctx->cgrp_cpuctx_entry;
    + if (add)
    + list_add(cpuctx_entry, this_cpu_ptr(&cgrp_cpuctx_list));
    + else
    + list_del(cpuctx_entry);
    }

    #else /* !CONFIG_CGROUP_PERF */
    @@ -2404,6 +2416,18 @@ static int __perf_install_in_context(vo
    raw_spin_lock(&task_ctx->lock);
    }

    +#ifdef CONFIG_CGROUP_PERF
    + if (is_cgroup_event(event)) {
    + /*
    + * If the current cgroup doesn't match the event's
    + * cgroup, we should not try to schedule it.
    + */
    + struct perf_cgroup *cgrp = perf_cgroup_from_task(current, ctx);
    + reprogram = cgroup_is_descendant(cgrp->css.cgroup,
    + event->cgrp->css.cgroup);
    + }
    +#endif
    +
    if (reprogram) {
    ctx_sched_out(ctx, cpuctx, EVENT_TIME);
    add_event_to_ctx(event, ctx);

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