[tip: perf/urgent] perf/cgroups: Install cgroup events to correct cpuctx

[tip-bot2 for Song Liu]

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     07c5972951f088094776038006a0592a46d14bbc
Gitweb:        https://git.kernel.org/tip/07c5972951f088094776038006a0592a46d14bbc
Author:        Song Liu <songliubraving@xxxxxx>
AuthorDate:    Wed, 22 Jan 2020 11:50:27 -08:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 28 Jan 2020 21:20:19 +01:00

perf/cgroups: Install cgroup events to correct cpuctx

cgroup events are always installed in the cpuctx. However, when it is not
installed via IPI, list_update_cgroup_event() adds it to cpuctx of current
CPU, which triggers list corruption:

  [] list_add double add: new=ffff888ff7cf0db0, prev=ffff888ff7ce82f0, next=ffff888ff7cf0db0.

To reproduce this, we can simply run:

  # perf stat -e cs -a &
  # perf stat -e cs -G anycgroup

Fix this by installing it to cpuctx that contains event->ctx, and the
proper cgrp_cpuctx_list.

Fixes: db0503e4f675 ("perf/core: Optimize perf_install_in_event()")
Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Song Liu <songliubraving@xxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200122195027.2112449-1-songliubraving@xxxxxx
---
 kernel/events/core.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2d9aeba..fdb7f7e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -951,9 +951,9 @@ list_update_cgroup_event(struct perf_event *event,
 
 	/*
 	 * Because cgroup events are always per-cpu events,
-	 * this will always be called from the right CPU.
+	 * @ctx == &cpuctx->ctx.
 	 */
-	cpuctx = __get_cpu_context(ctx);
+	cpuctx = container_of(ctx, struct perf_cpu_context, ctx);
 
 	/*
 	 * Since setting cpuctx->cgrp is conditional on the current @cgrp
@@ -979,7 +979,8 @@ list_update_cgroup_event(struct perf_event *event,
 
 	cpuctx_entry = &cpuctx->cgrp_cpuctx_entry;
 	if (add)
-		list_add(cpuctx_entry, this_cpu_ptr(&cgrp_cpuctx_list));
+		list_add(cpuctx_entry,
+			 per_cpu_ptr(&cgrp_cpuctx_list, event->cpu));
 	else
 		list_del(cpuctx_entry);
 }