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From: Peter Zijlstra <peterz@infradead.org>
To: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>,
	Sasha Levin <sasha.levin@oracle.com>,
	akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org,
	cgroups@vger.kernel.org, linux-mm@kvack.org,
	vdavydov@parallels.com, kernel-team@fb.com
Subject: Re: [PATCH 1/2] memcg: flatten task_struct->memcg_oom
Date: Wed, 25 Nov 2015 16:02:07 +0100
Message-ID: <20151125150207.GM11639@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20151125144354.GB17308@twins.programming.kicks-ass.net>

On Wed, Nov 25, 2015 at 03:43:54PM +0100, Peter Zijlstra wrote:
> On Mon, Sep 21, 2015 at 04:01:41PM -0400, Tejun Heo wrote:
> > So, the only way the patch could have caused the above is if someone
> > who isn't the task itself is writing to the bitfields while the task
> > is running.  Looking through the fields, ->sched_reset_on_fork seems a
> > bit suspicious.  __sched_setscheduler() looks like it can modify the
> > bit while the target task is running.  Peter, am I misreading the
> > code?
> 
> Nope, that's quite possible. Looks like we need to break up those
> bitfields a bit. All the scheduler ones should be serialized by
> scheduler locks, but the others are fair game.

Maybe something like so; but my brain is a complete mess today.

---
 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 f425aac63317..b474e0f05327 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 __padding_sched:29;
+
+	/* 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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  reply index

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-13 18:59 Tejun Heo
2015-09-13 19:00 ` [PATCH v3 2/2] memcg: punt high overage reclaim to return-to-userland path Tejun Heo
2015-09-15  7:47   ` Johannes Weiner
2015-09-15 15:53     ` Tejun Heo
2015-09-15 16:12       ` Johannes Weiner
2015-09-15 16:22         ` Tejun Heo
2015-09-15 16:33           ` Johannes Weiner
2015-09-15  7:37 ` [PATCH 1/2] memcg: flatten task_struct->memcg_oom Johannes Weiner
2015-09-20 14:45 ` Sasha Levin
2015-09-21 20:01   ` Tejun Heo
2015-09-30 18:54     ` Tejun Heo
2015-11-25 14:43     ` Peter Zijlstra
2015-11-25 15:02       ` Peter Zijlstra [this message]
2015-11-25 15:31         ` Andrey Ryabinin
2015-11-25 17:34           ` Dmitry Vyukov
2015-11-25 17:44           ` Peter Zijlstra
2015-12-11 16:25             ` Tejun Heo
2015-12-15 19:22               ` Peter Zijlstra
2015-12-30  9:23                 ` [PATCH v4.4-rc7] sched: isolate task_struct bitfields according to synchronization domains Tejun Heo
2015-12-30 20:10                   ` Linus Torvalds
2015-12-30 20:17                     ` Linus Torvalds
2015-12-30 20:41                     ` Tejun Heo
2015-12-30 20:43                       ` Linus Torvalds
2016-01-01  2:56                     ` [PATCH v4.4-rc7] sched: move sched lock synchronized bitfields in task_struct into ->atomic_flags Tejun Heo
2016-01-06 13:44                       ` Tejun Heo
  -- strict thread matches above, loose matches on Subject: below --
2015-08-28 22:01 [PATCH 1/2] memcg: flatten task_struct->memcg_oom Tejun Heo
2015-09-01 15:25 ` Michal Hocko
2015-09-02 11:45 ` Vladimir Davydov

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