Re: [PATCH] sched: Make dl_task_time() use task_rq_lock()
From: Peter Zijlstra
Date: Tue Feb 17 2015 - 08:32:37 EST
On Tue, Feb 17, 2015 at 01:31:39PM +0100, Peter Zijlstra wrote:
> On Tue, Feb 17, 2015 at 02:33:58PM +0300, Kirill Tkhai wrote:
> > So, we move task_rq_lock() to sched.h, and dl_task_timer() uses it?
> Yep, like this. I've also modified your earlier patch to dl_task_time()
> back to its original form.
> Subject: sched: Make dl_task_time() use task_rq_lock()
> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Date: Tue Feb 17 13:22:25 CET 2015
> Kirill reported that a dl task can be throttled and dequeued at the
> same time. This happens, when it becomes throttled in schedule(),
> which is called to go to sleep:
> current->state = TASK_INTERRUPTIBLE;
> prev->on_rq = 0;
> This invalidates the assumption from commit 0f397f2c90ce ("sched/dl:
> Fix race in dl_task_timer()"):
> "The only reason we don't strictly need ->pi_lock now is because
> we're guaranteed to have p->state == TASK_RUNNING here and are
> thus free of ttwu races".
> And therefore we have to use the full task_rq_lock() here.
> This further amends the fact that we forgot to update the rq lock loop
> for TASK_ON_RQ_MIGRATE, from commit cca26e8009d1 ("sched: Teach
> scheduler to understand TASK_ON_RQ_MIGRATING state").
> Reported-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> kernel/sched/core.c | 76 ------------------------------------------------
> kernel/sched/deadline.c | 12 +------
> kernel/sched/sched.h | 76 ++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 79 insertions(+), 85 deletions(-)
Duh, I put it under CONFIG_SMP, /me changes patch to not do this.
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