linux-kernel - [tip:sched/core] sched/core: Fix unserialized r-m-w scribbling stuff

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Date:	Wed, 6 Jan 2016 10:48:15 -0800
From:	tip-bot for Peter Zijlstra <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	tglx@...utronix.de, tj@...nel.org, hpa@...or.com,
	sasha.levin@...cle.com, torvalds@...ux-foundation.org,
	mingo@...nel.org, peterz@...radead.org, dvyukov@...gle.com,
	linux-kernel@...r.kernel.org
Subject: [tip:sched/core] sched/core:
  Fix unserialized r-m-w scribbling stuff

Commit-ID:  be958bdc96f18bc1356177bbb79d46ea0c037b96
Gitweb:     http://git.kernel.org/tip/be958bdc96f18bc1356177bbb79d46ea0c037b96
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Wed, 25 Nov 2015 16:02:07 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 6 Jan 2016 11:01:07 +0100

sched/core: Fix unserialized r-m-w scribbling stuff

Some of the sched bitfieds (notably sched_reset_on_fork) can be set
on other than current, this can cause the r-m-w to race with other
updates.

Since all the sched bits are serialized by scheduler locks, pull them
in a separate word.

Reported-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sasha Levin <sasha.levin@...cle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: akpm@...ux-foundation.org
Cc: hannes@...xchg.org
Cc: mhocko@...nel.org
Cc: vdavydov@...allels.com
Link: http://lkml.kernel.org/r/20151125150207.GM11639@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 include/linux/sched.h | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9cf9dd1..fa39434 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1455,14 +1455,15 @@ struct task_struct {
 	/* Used for emulating ABI behavior of previous Linux versions */
 	unsigned int personality;
 
-	unsigned in_execve:1;	/* Tell the LSMs that the process is doing an
-				 * execve */
-	unsigned in_iowait:1;
-
-	/* Revert to default priority/policy when forking */
+	/* scheduler bits, serialized by scheduler locks */
 	unsigned sched_reset_on_fork:1;
 	unsigned sched_contributes_to_load:1;
 	unsigned sched_migrated:1;
+	unsigned :0; /* force alignment to the next boundary */
+
+	/* unserialized, strictly 'current' */
+	unsigned in_execve:1; /* bit to tell LSMs we're in execve */
+	unsigned in_iowait:1;
 #ifdef CONFIG_MEMCG
 	unsigned memcg_may_oom:1;
 #endif
--
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