perf/core: Fix installing cgroup events on CPU

[ 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>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index bd9d4d3..d0f13b6 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -900,27 +900,39 @@ list_update_cgroup_event(struct perf_event *event,
        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(void *info)
                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);