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@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akpm@linux-foundation.org
Cc: hannes@cmpxchg.org
Cc: mhocko@kernel.org
Cc: vdavydov@parallels.com
Link: http://lkml.kernel.org/r/20151125150207.GM11639@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9cf9dd1c4cbedb7392132c3657aa3398db17e6d2..fa39434e3fdd1c74eaf18dd4a31dae0b69a9db1c 100644 (file)
--- 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