linux-kernel - [tip:perf/urgent] perf: Fix task context scheduling

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Message-ID: <tip-ab711fe08297de1485fff0a366e6db8828cafd6a@git.kernel.org>
Date:	Thu, 31 Mar 2011 12:41:57 GMT
From:	tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, jolsa@...hat.com, tglx@...utronix.de,
	oleg@...hat.com, mingo@...e.hu
Subject: [tip:perf/urgent] perf: Fix task context scheduling

Commit-ID:  ab711fe08297de1485fff0a366e6db8828cafd6a
Gitweb:     http://git.kernel.org/tip/ab711fe08297de1485fff0a366e6db8828cafd6a
Author:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Thu, 31 Mar 2011 10:29:26 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Thu, 31 Mar 2011 13:02:55 +0200

perf: Fix task context scheduling

Jiri reported:

 |
 | - once an event is created by sys_perf_event_open, task context
 |   is created and it stays even if the event is closed, until the
 |   task is finished ... thats what I see in code and I assume it's
 |   correct
 |
 | - when the task opens event, perf_sched_events jump label is
 |   incremented and following callbacks are started from scheduler
 |
 |         __perf_event_task_sched_in
 |         __perf_event_task_sched_out
 |
 |   These callback *in/out set/unset cpuctx->task_ctx value to the
 |   task context.
 |
 | - close is called on event on CPU 0:
 |         - the task is scheduled on CPU 0
 |         - __perf_event_task_sched_in is called
 |         - cpuctx->task_ctx is set
 |         - perf_sched_events jump label is decremented and == 0
 |         - __perf_event_task_sched_out is not called
 |         - cpuctx->task_ctx on CPU 0 stays set
 |
 | - exit is called on CPU 1:
 |         - the task is scheduled on CPU 1
 |         - perf_event_exit_task is called
 |         - task_ctx_sched_out unsets cpuctx->task_ctx on CPU 1
 |         - put_ctx destroys the context
 |
 | - another call of perf_rotate_context on CPU 0 will use invalid
 |   task_ctx pointer, and eventualy panic.
 |

Cure this the simplest possibly way by partially reverting the
jump_label optimization for the sched_out case.

Reported-and-tested-by: Jiri Olsa <jolsa@...hat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: <stable@...nel.org> # .37+
LKML-Reference: <1301520405.4859.213.camel@...ns>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 include/linux/perf_event.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 311b4dc..04d75a8 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1086,7 +1086,7 @@ void perf_event_task_sched_out(struct task_struct *task, struct task_struct *nex
 {
 	perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 1, NULL, 0);

-	COND_STMT(&perf_sched_events, __perf_event_task_sched_out(task, next));
+	__perf_event_task_sched_out(task, next);
 }

 extern void perf_event_mmap(struct vm_area_struct *vma);
--
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