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) <pet...@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
