From: Peter Zijlstra <peterz@infradead.org>
To: Petr Mladek <pmladek@suse.com>
Cc: gor@linux.ibm.com, jpoimboe@redhat.com, jikos@kernel.org,
mbenes@suse.cz, mingo@kernel.org, linux-kernel@vger.kernel.org,
joe.lawrence@redhat.com, fweisbec@gmail.com, tglx@linutronix.de,
hca@linux.ibm.com, svens@linux.ibm.com, sumanthk@linux.ibm.com,
live-patching@vger.kernel.org, paulmck@kernel.org,
rostedt@goodmis.org, x86@kernel.org
Subject: Re: [PATCH v2 03/11] sched,livepatch: Use task_call_func()
Date: Tue, 5 Oct 2021 16:03:43 +0200 [thread overview]
Message-ID: <YVxbP5fFLY10mqhy@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <YVw5qO0rLA/GduFm@alley>
On Tue, Oct 05, 2021 at 01:40:24PM +0200, Petr Mladek wrote:
> On Wed 2021-09-29 17:17:26, Peter Zijlstra wrote:
> > Instead of frobbing around with scheduler internals, use the shiny new
> > task_call_func() interface.
> >
> > --- a/kernel/livepatch/transition.c
> > +++ b/kernel/livepatch/transition.c
> > @@ -274,6 +266,22 @@ static int klp_check_stack(struct task_s
> > return 0;
> > }
> >
> > +static int klp_check_and_switch_task(struct task_struct *task, void *arg)
> > +{
> > + int ret;
> > +
> > + if (task_curr(task))
>
> This must be
>
> if (task_curr(task) && task != current)
>
> , otherwise the task is not able to migrate itself. The condition was
> lost when reshuffling the original code, see below.
Urgh, yeah, I misread that and figued task_curr() should already capture
current, but the extra clause excludes current :/
> JFYI, I have missed it during review. I am actually surprised that the
> process could check its own stack reliably. But it seems to work.
Ah, unwinding yourself is actually the only sane option ;-)
> > - rq = task_rq_lock(task, &flags);
> > + ret = task_call_func(task, klp_check_and_switch_task, &old_name);
>
> It looks correct. JFYI, this is why:
>
> The logic seems to be exactly the same, except for the one fallout
> mentioned above. So the only problem might be races.
>
> The only important thing is that the task must not be running on any CPU
> when klp_check_stack(task, arg) is called. By other word, the stack
> must stay the same when being checked.
>
> The original code prevented races by taking task_rq_lock().
> And task_call_func() is slightly more relaxed but it looks safe enough:
>
> + it still takes rq lock when the task is in runnable state.
> + it always takes p->pi_lock that prevents moving the task
> into runnable state by try_to_wake_up().
Correct, the new task_call_func() is trying hard to not take rq->lock,
but should be effectively identical to task_rq_lock().
> With the added (task != current) check:
Done
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> Tested-by: Petr Mladek <pmladek@suse.com>
Thanks!
next prev parent reply other threads:[~2021-10-05 14:06 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-29 15:17 [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 01/11] sched: Improve try_invoke_on_locked_down_task() Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 02/11] sched,rcu: Rework try_invoke_on_locked_down_task() Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 03/11] sched,livepatch: Use task_call_func() Peter Zijlstra
2021-10-05 11:40 ` Petr Mladek
2021-10-05 14:03 ` Peter Zijlstra [this message]
2021-10-06 8:59 ` Miroslav Benes
2021-09-29 15:17 ` [PATCH v2 04/11] sched: Simplify wake_up_*idle*() Peter Zijlstra
2021-10-13 14:32 ` Qian Cai
2021-10-19 3:47 ` Qian Cai
2021-10-19 8:56 ` Peter Zijlstra
2021-10-19 9:10 ` Peter Zijlstra
2021-10-19 15:32 ` Qian Cai
2021-10-19 15:50 ` Peter Zijlstra
2021-10-19 19:22 ` Qian Cai
2021-10-19 20:27 ` Peter Zijlstra
[not found] ` <CGME20211022134630eucas1p2e79e2816587d182c580459d567c1f2a9@eucas1p2.samsung.com>
2021-10-22 13:46 ` Marek Szyprowski
2021-09-29 15:17 ` [PATCH v2 05/11] sched,livepatch: Use wake_up_if_idle() Peter Zijlstra
2021-10-05 12:00 ` Petr Mladek
2021-10-06 9:16 ` Miroslav Benes
2021-10-07 9:18 ` Vasily Gorbik
2021-10-07 10:02 ` Peter Zijlstra
2021-10-13 19:37 ` Arnd Bergmann
2021-10-14 10:42 ` Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 06/11] context_tracking: Prefix user_{enter,exit}*() Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 07/11] context_tracking: Add an atomic sequence/state count Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 08/11] context_tracking,rcu: Replace RCU dynticks counter with context_tracking Peter Zijlstra
2021-09-29 18:37 ` Paul E. McKenney
2021-09-29 19:09 ` Peter Zijlstra
2021-09-29 19:11 ` Peter Zijlstra
2021-09-29 19:13 ` Peter Zijlstra
2021-09-29 19:24 ` Peter Zijlstra
2021-09-29 19:45 ` Paul E. McKenney
2021-09-29 18:54 ` Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 09/11] context_tracking,livepatch: Dont disturb NOHZ_FULL Peter Zijlstra
2021-10-06 8:12 ` Petr Mladek
2021-10-06 9:04 ` Peter Zijlstra
2021-10-06 10:29 ` Petr Mladek
2021-10-06 11:41 ` Peter Zijlstra
2021-10-06 11:48 ` Miroslav Benes
2021-09-29 15:17 ` [RFC][PATCH v2 10/11] livepatch: Remove klp_synchronize_transition() Peter Zijlstra
2021-10-06 12:30 ` Petr Mladek
2021-09-29 15:17 ` [RFC][PATCH v2 11/11] context_tracking,x86: Fix text_poke_sync() vs NOHZ_FULL Peter Zijlstra
2021-10-21 18:39 ` Marcelo Tosatti
2021-10-21 18:40 ` Marcelo Tosatti
2021-10-21 19:25 ` Peter Zijlstra
2021-10-21 19:57 ` Marcelo Tosatti
2021-10-21 20:18 ` Peter Zijlstra
2021-10-26 18:19 ` Marcelo Tosatti
2021-10-26 19:38 ` Peter Zijlstra
2021-09-29 18:03 ` [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Paul E. McKenney
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