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From: Eric Biggers <ebiggers@kernel.org>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Peter Zijlstra <peterz@infradead.org>,
	tglx@linutronix.de, frederic@kernel.org,
	linux-kernel@vger.kernel.org, x86@kernel.org, cai@lca.pw,
	mgorman@techsingularity.net
Subject: Re: [RFC][PATCH 7/7] sched: Replace rq::wake_list
Date: Tue, 9 Jun 2020 13:21:34 -0700	[thread overview]
Message-ID: <20200609202134.GA1105@sol.localdomain> (raw)
In-Reply-To: <53318971-561c-b445-0408-530b3d3ba44e@roeck-us.net>

On Sat, Jun 06, 2020 at 04:13:33PM -0700, Guenter Roeck wrote:
> On 6/5/20 9:15 AM, Eric Biggers wrote:
> > On Fri, Jun 05, 2020 at 09:41:54AM +0200, Peter Zijlstra wrote:
> >> On Thu, Jun 04, 2020 at 05:24:33PM -0700, Eric Biggers wrote:
> >>> On Thu, Jun 04, 2020 at 07:18:37AM -0700, Guenter Roeck wrote:
> >>>> On Tue, May 26, 2020 at 06:11:04PM +0200, Peter Zijlstra wrote:
> >>>>> The recent commit: 90b5363acd47 ("sched: Clean up scheduler_ipi()")
> >>>>> got smp_call_function_single_async() subtly wrong. Even though it will
> >>>>> return -EBUSY when trying to re-use a csd, that condition is not
> >>>>> atomic and still requires external serialization.
> >>>>>
> >>>>> The change in ttwu_queue_remote() got this wrong.
> >>>>>
> >>>>> While on first reading ttwu_queue_remote() has an atomic test-and-set
> >>>>> that appears to serialize the use, the matching 'release' is not in
> >>>>> the right place to actually guarantee this serialization.
> >>>>>
> >>>>> The actual race is vs the sched_ttwu_pending() call in the idle loop;
> >>>>> that can run the wakeup-list without consuming the CSD.
> >>>>>
> >>>>> Instead of trying to chain the lists, merge them.
> >>>>>
> >>>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> >>>>> ---
> >>>> ...
> >>>>> +	/*
> >>>>> +	 * Assert the CSD_TYPE_TTWU layout is similar enough
> >>>>> +	 * for task_struct to be on the @call_single_queue.
> >>>>> +	 */
> >>>>> +	BUILD_BUG_ON(offsetof(struct task_struct, wake_entry_type) - offsetof(struct task_struct, wake_entry) !=
> >>>>> +		     offsetof(struct __call_single_data, flags) - offsetof(struct __call_single_data, llist));
> >>>>> +
> >>>>
> >>>> There is no guarantee in C that
> >>>>
> >>>> 	type1 a;
> >>>> 	type2 b;
> >>>>
> >>>> in two different data structures means that offsetof(b) - offsetof(a)
> >>>> is the same in both data structures unless attributes such as
> >>>> __attribute__((__packed__)) are used.
> >>>>
> >>>> As result, this does and will cause a variety of build errors depending
> >>>> on the compiler version and compile flags.
> >>>>
> >>>> Guenter
> >>>
> >>> Yep, this breaks the build for me.
> >>
> >> -ENOCONFIG
> > 
> > For me, the problem seems to be randstruct.  To reproduce, you can use
> > (on x86_64):
> > 
> > 	make defconfig
> > 	echo CONFIG_GCC_PLUGIN_RANDSTRUCT=y >> .config
> > 	make olddefconfig
> > 	make kernel/smp.o
> > 
> 
> I confirmed that disabling CONFIG_GCC_PLUGIN_RANDSTRUCT "fixes" the problem
> in my test builds. Maybe it would make sense to mark that configuration option
> for the time being as BROKEN.
> 

Still occurring on Linus' tree.  This needs to be fixed.  (And not by removing
support for randstruct; that's not a "fix"...)

Shouldn't the kbuild test robot have caught this?

- Eric

  reply	other threads:[~2020-06-09 20:21 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-26 16:10 [RFC][PATCH 0/7] Fix the scheduler-IPI mess Peter Zijlstra
2020-05-26 16:10 ` [RFC][PATCH 1/7] sched: Fix smp_call_function_single_async() usage for ILB Peter Zijlstra
2020-05-26 23:56   ` Frederic Weisbecker
2020-05-27 10:23   ` Vincent Guittot
2020-05-27 11:28     ` Frederic Weisbecker
2020-05-27 12:07       ` Vincent Guittot
2020-05-29 15:26   ` Valentin Schneider
2020-06-01  9:52   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-06-01 11:40     ` Frederic Weisbecker
2020-05-26 16:10 ` [RFC][PATCH 2/7] smp: Optimize flush_smp_call_function_queue() Peter Zijlstra
2020-05-28 12:28   ` Frederic Weisbecker
2020-06-01  9:52   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-05-26 16:11 ` [RFC][PATCH 3/7] smp: Move irq_work_run() out of flush_smp_call_function_queue() Peter Zijlstra
2020-05-29 13:04   ` Frederic Weisbecker
2020-06-01  9:52   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-05-26 16:11 ` [RFC][PATCH 4/7] smp: Optimize send_call_function_single_ipi() Peter Zijlstra
2020-05-27  9:56   ` Peter Zijlstra
2020-05-27 10:15     ` Peter Zijlstra
2020-05-27 15:56       ` Paul E. McKenney
2020-05-27 16:35         ` Peter Zijlstra
2020-05-27 17:12           ` Peter Zijlstra
2020-05-27 19:39             ` Paul E. McKenney
2020-05-28  1:35               ` Joel Fernandes
2020-05-28  8:59             ` [tip: core/rcu] rcu: Allow for smp_call_function() running callbacks from idle tip-bot2 for Peter Zijlstra
2021-01-21 16:56             ` [RFC][PATCH 4/7] smp: Optimize send_call_function_single_ipi() Peter Zijlstra
2021-01-22  0:20               ` Paul E. McKenney
2021-01-22  8:31                 ` Peter Zijlstra
2021-01-22 15:35                   ` Paul E. McKenney
2020-05-29 13:01   ` Frederic Weisbecker
2020-06-01  9:52   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-05-26 16:11 ` [RFC][PATCH 5/7] irq_work, smp: Allow irq_work on call_single_queue Peter Zijlstra
2020-05-28 23:40   ` Frederic Weisbecker
2020-05-29 13:36     ` Peter Zijlstra
2020-06-05  9:37       ` Peter Zijlstra
2020-06-05 15:02         ` Frederic Weisbecker
2020-06-05 16:17           ` Peter Zijlstra
2020-06-05 15:24         ` Kees Cook
2020-06-10 13:24         ` Frederic Weisbecker
2020-06-01  9:52   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-05-26 16:11 ` [RFC][PATCH 6/7] sched: Add rq::ttwu_pending Peter Zijlstra
2020-06-01  9:52   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-05-26 16:11 ` [RFC][PATCH 7/7] sched: Replace rq::wake_list Peter Zijlstra
2020-05-29 15:10   ` Valdis Klētnieks
2020-06-01  9:52   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-06-02 15:16     ` Frederic Weisbecker
2020-06-04 14:18   ` [RFC][PATCH 7/7] " Guenter Roeck
2020-06-05  0:24     ` Eric Biggers
2020-06-05  7:41       ` Peter Zijlstra
2020-06-05 16:15         ` Eric Biggers
2020-06-06 23:13           ` Guenter Roeck
2020-06-09 20:21             ` Eric Biggers [this message]
2020-06-09 21:25               ` Guenter Roeck
2020-06-09 21:38                 ` Eric Biggers
2020-06-09 22:06                   ` Peter Zijlstra
2020-06-09 23:03                     ` Guenter Roeck
2020-06-10  9:09                       ` Peter Zijlstra
2020-06-18 17:57                 ` Steven Rostedt
2020-06-18 19:06                   ` Guenter Roeck
2020-06-09 22:07               ` Peter Zijlstra
2020-06-05  8:10     ` Peter Zijlstra
2020-06-05 13:33       ` Guenter Roeck
2020-06-05 14:09         ` Peter Zijlstra

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