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Message-ID: <20200706234136.GS9247@paulmck-ThinkPad-P72>
Date: Mon, 6 Jul 2020 16:41:36 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Marco Elver <elver@...gle.com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Masahiro Yamada <masahiroy@...nel.org>,
Will Deacon <will@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Kees Cook <keescook@...omium.org>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
linux-arch <linux-arch@...r.kernel.org>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH 00/22] add support for Clang LTO
On Mon, Jul 06, 2020 at 09:40:12PM +0200, Peter Zijlstra wrote:
> On Mon, Jul 06, 2020 at 11:39:33AM -0700, Paul E. McKenney wrote:
> > On Mon, Jul 06, 2020 at 08:29:26PM +0200, Peter Zijlstra wrote:
> > > On Mon, Jul 06, 2020 at 09:26:33AM -0700, Paul E. McKenney wrote:
>
> > > If they do not consider their Linux OS running correctly :-)
> >
> > Many of them really do not care at all. In fact, some would consider
> > Linux failing to run as an added bonus.
>
> This I think is why we have compiler people in the thread that care a
> lot more.
Here is hoping! ;-)
> > > > Nevertheless, yes, control dependencies also need attention.
> > >
> > > Today I added one more \o/
> >
> > Just make sure you continually check to make sure that compilers
> > don't break it, along with the others you have added. ;-)
>
> There's:
>
> kernel/locking/mcs_spinlock.h: smp_cond_load_acquire(l, VAL); \
> kernel/sched/core.c: smp_cond_load_acquire(&p->on_cpu, !VAL);
> kernel/smp.c: smp_cond_load_acquire(&csd->node.u_flags, !(VAL & CSD_FLAG_LOCK));
>
> arch/x86/kernel/alternative.c: atomic_cond_read_acquire(&desc.refs, !VAL);
> kernel/locking/qrwlock.c: atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
> kernel/locking/qrwlock.c: atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
> kernel/locking/qrwlock.c: atomic_cond_read_acquire(&lock->cnts, VAL == _QW_WAITING);
> kernel/locking/qspinlock.c: atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_MASK));
> kernel/locking/qspinlock.c: val = atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK));
>
> include/linux/refcount.h: smp_acquire__after_ctrl_dep();
> ipc/mqueue.c: smp_acquire__after_ctrl_dep();
> ipc/msg.c: smp_acquire__after_ctrl_dep();
> ipc/sem.c: smp_acquire__after_ctrl_dep();
> kernel/locking/rwsem.c: smp_acquire__after_ctrl_dep();
> kernel/sched/core.c: smp_acquire__after_ctrl_dep();
>
> kernel/events/ring_buffer.c:__perf_output_begin()
>
> And I'm fairly sure I'm forgetting some... One could argue there's too
> many of them to check already.
>
> Both GCC and CLANG had better think about it.
That would be good!
I won't list the number of address/data dependencies given that there
are well over a thousand of them.
Thanx, Paul
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