linux-kernel - [PATCH] perf: correct ctx_event_type in ctx

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180306055504.3283731-1-songliubraving@fb.com>
Date:   Mon, 5 Mar 2018 21:55:04 -0800
From:   Song Liu <songliubraving@...com>
To:     <linux-kernel@...r.kernel.org>, <peterz@...radead.org>,
        <jolsa@...hat.com>
CC:     <kernel-team@...com>, <ephiepark@...com>,
        Song Liu <songliubraving@...com>
Subject: [PATCH] perf: correct ctx_event_type in ctx_resched()

In ctx_resched(), EVENT_FLEXIBLE should be sched_out when EVENT_PINNED is
added. However, ctx_resched() calculates ctx_event_type before checking
this condition. As a result, pinned events will NOT get higher priority
than flexible events.

The following shows this issue on an Intel CPU (where ref-cycles can
only use one hardware counter).

  1. First start:
       perf stat -C 0 -e ref-cycles  -I 1000
  2. Then, in the second console, run:
       perf stat -C 0 -e ref-cycles:D -I 1000

The second perf uses pinned events, which is expected to have higher
priority. However, because it failed in ctx_resched(). It is never
run.

This patch fixes this by calculating ctx_event_type after re-evaluating
event_type.

Fixes: 487f05e18aa4 ("perf/core: Optimize event rescheduling on active contexts")
Signed-off-by: Song Liu <songliubraving@...com>
Reported-by: Ephraim Park <ephiepark@...com>
---
 kernel/events/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5789810..cf52fc0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2246,7 +2246,7 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
 			struct perf_event_context *task_ctx,
 			enum event_type_t event_type)
 {
-	enum event_type_t ctx_event_type = event_type & EVENT_ALL;
+	enum event_type_t ctx_event_type;
 	bool cpu_event = !!(event_type & EVENT_CPU);
 
 	/*
@@ -2256,6 +2256,8 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
 	if (event_type & EVENT_PINNED)
 		event_type |= EVENT_FLEXIBLE;
 
+	ctx_event_type = event_type & EVENT_ALL;
+
 	perf_pmu_disable(cpuctx->ctx.pmu);
 	if (task_ctx)
 		task_ctx_sched_out(cpuctx, task_ctx, event_type);
-- 
2.9.5