linux-kernel - Re: [PATCH v3 04/25] kcsan: Add core support for a subset of weak memory modeling

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Message-ID: <20211203210856.GA712591@paulmck-ThinkPad-P17-Gen-1>
Date:   Fri, 3 Dec 2021 13:08:56 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Marco Elver <elver@...gle.com>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Waiman Long <longman@...hat.com>,
        Will Deacon <will@...nel.org>, kasan-dev@...glegroups.com,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, llvm@...ts.linux.dev, x86@...nel.org
Subject: Re: [PATCH v3 04/25] kcsan: Add core support for a subset of weak
 memory modeling

On Fri, Dec 03, 2021 at 08:50:20AM -0800, Paul E. McKenney wrote:
> On Fri, Dec 03, 2021 at 09:56:45AM +0100, Marco Elver wrote:
> > On Tue, Nov 30, 2021 at 12:44PM +0100, Marco Elver wrote:
> > [...]
> > > v3:
> > > * Remove kcsan_noinstr hackery, since we now try to avoid adding any
> > >   instrumentation to .noinstr.text in the first place.
> > [...]
> > 
> > I missed some cleanups after changes from v2 to v3 -- the below cleanup
> > is missing.
> > 
> > Full replacement patch attached.
> 
> I pulled this into -rcu with the other patches from your v3 post, thank
> you all!

A few quick tests located the following:

[    0.635383] INFO: trying to register non-static key.
[    0.635804] The code is fine but needs lockdep annotation, or maybe
[    0.636194] you didn't initialize this object before use?
[    0.636194] turning off the locking correctness validator.
[    0.636194] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.16.0-rc1+ #3208
[    0.636194] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014
[    0.636194] Call Trace:
[    0.636194]  <TASK>
[    0.636194]  dump_stack_lvl+0x88/0xd8
[    0.636194]  dump_stack+0x15/0x1b
[    0.636194]  register_lock_class+0x6b3/0x840
[    0.636194]  ? __this_cpu_preempt_check+0x1d/0x30
[    0.636194]  __lock_acquire+0x81/0xee0
[    0.636194]  ? lock_is_held_type+0xf1/0x160
[    0.636194]  lock_acquire+0xce/0x230
[    0.636194]  ? test_barrier+0x490/0x14c7
[    0.636194]  ? lock_is_held_type+0xf1/0x160
[    0.636194]  ? test_barrier+0x490/0x14c7
[    0.636194]  _raw_spin_lock+0x36/0x50
[    0.636194]  ? test_barrier+0x490/0x14c7
[    0.636194]  ? kcsan_init+0xf/0x80
[    0.636194]  test_barrier+0x490/0x14c7
[    0.636194]  ? kcsan_debugfs_init+0x1f/0x1f
[    0.636194]  kcsan_selftest+0x47/0xa0
[    0.636194]  do_one_initcall+0x104/0x230
[    0.636194]  ? rcu_read_lock_sched_held+0x5b/0xc0
[    0.636194]  ? kernel_init+0x1c/0x200
[    0.636194]  do_initcall_level+0xa5/0xb6
[    0.636194]  do_initcalls+0x66/0x95
[    0.636194]  do_basic_setup+0x1d/0x23
[    0.636194]  kernel_init_freeable+0x254/0x2ed
[    0.636194]  ? rest_init+0x290/0x290
[    0.636194]  kernel_init+0x1c/0x200
[    0.636194]  ? rest_init+0x290/0x290
[    0.636194]  ret_from_fork+0x22/0x30
[    0.636194]  </TASK>

When running without the new patch series, this splat does not appear.

Do I need a toolchain upgrade?  I see the Clang 14.0 in the cover letter,
but that seems to apply only to non-x86 architectures.

$ clang-11 -v
Ubuntu clang version 11.1.0-++20210805102428+1fdec59bffc1-1~exp1~20210805203044.169

							Thanx, Paul