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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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