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: Thu, 4 Jun 2020 17:24:33 -0700 [thread overview]
Message-ID: <20200605002433.GA148196@sol.localdomain> (raw)
In-Reply-To: <20200604141837.GA179816@roeck-us.net>
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.
CC kernel/smp.o
In file included from ./arch/x86/include/asm/atomic.h:5,
from ./include/linux/atomic.h:7,
from ./include/linux/llist.h:51,
from ./include/linux/irq_work.h:5,
from kernel/smp.c:10:
kernel/smp.c: In function ‘smp_init’:
./include/linux/compiler.h:403:38: error: call to ‘__compiletime_assert_68’ declared with attribute error: BUILD_BUG_ON failed: 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)
403 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
| ^
./include/linux/compiler.h:384:4: note: in definition of macro ‘__compiletime_assert’
384 | prefix ## suffix(); \
| ^~~~~~
./include/linux/compiler.h:403:2: note: in expansion of macro ‘_compiletime_assert’
403 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
| ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
| ^~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
50 | BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
| ^~~~~~~~~~~~~~~~
kernel/smp.c:687:2: note: in expansion of macro ‘BUILD_BUG_ON’
687 | BUILD_BUG_ON(offsetof(struct task_struct, wake_entry_type) - offsetof(struct task_struct, wake_entry) !=
| ^~~~~~~~~~~~
make[1]: *** [scripts/Makefile.build:267: kernel/smp.o] Error 1
make: *** [Makefile:1735: kernel] Error 2
next prev parent reply other threads:[~2020-06-05 0:24 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 [this message]
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
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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