linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Marco Elver <elver@google.com>
To: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [PATCH v5 00/18] Rework READ_ONCE() to improve codegen
Date: Thu, 14 May 2020 09:31:49 +0200	[thread overview]
Message-ID: <CANpmjNOAi2K6knC9OFUGjpMo-rvtLDzKMb==J=vTRkmaWctFaQ@mail.gmail.com> (raw)
In-Reply-To: <20200513212520.GC28594@willie-the-truck>

On Wed, 13 May 2020 at 23:25, Will Deacon <will@kernel.org> wrote:
>
> On Wed, May 13, 2020 at 08:54:03PM +0200, Marco Elver wrote:
> > On Wed, 13 May 2020 at 19:47, Will Deacon <will@kernel.org> wrote:
> > > On Wed, May 13, 2020 at 07:32:58PM +0200, Marco Elver wrote:
> > > > - We do *not* want the call to __read_once_word_nocheck if we have
> > > > __no_sanitize_or_inline. AFAIK that's the main problem -- this applies
> > > > to both KASAN and KCSAN.
> > >
> > > Sorry, I should've been more explicit. The code above, with KASAN enabled,
> > > compiles to:
> > >
> > > ffffffff810a2d50 <foo>:
> > > ffffffff810a2d50:       48 8b 07                mov    (%rdi),%rax
> > > ffffffff810a2d53:       c3                      retq
> > >
> > > but with KCSAN enabled, compiles to:
> > >
> > > ffffffff8109ecd0 <foo>:
> > > ffffffff8109ecd0:       53                      push   %rbx
> > > ffffffff8109ecd1:       48 89 fb                mov    %rdi,%rbx
> > > ffffffff8109ecd4:       48 8b 7c 24 08          mov    0x8(%rsp),%rdi
> > > ffffffff8109ecd9:       e8 52 9c 1a 00          callq  ffffffff81248930 <__tsan_func_entry>
> > > ffffffff8109ecde:       48 89 df                mov    %rbx,%rdi
> > > ffffffff8109ece1:       e8 1a 00 00 00          callq  ffffffff8109ed00 <__read_once_word_nocheck>
> > > ffffffff8109ece6:       48 89 c3                mov    %rax,%rbx
> > > ffffffff8109ece9:       e8 52 9c 1a 00          callq  ffffffff81248940 <__tsan_func_exit>
> > > ffffffff8109ecee:       48 89 d8                mov    %rbx,%rax
> > > ffffffff8109ecf1:       5b                      pop    %rbx
> > > ffffffff8109ecf2:       c3                      retq
> > >
> > > Is that expected? There don't appear to be any more annotations to throw
> > > at it.
> >
> > Right, so this is expected.
>
> Fair enough, I just found it weird since it's different to the usual
> "disable instrumentation/trace" function annotations.
>
> > We can definitely make __tsan_func_entry/exit disappear with Clang, with
> > GCC it's going to be a while if we want to fix it.
> >
> > If we remove 'noinline' from __no_kcsan_or_inline, we no longer get
> > the call to __read_once_word_nocheck above! But...
> >
> > For KCSAN we force 'noinline' because older compilers still inline and
> > then instrument small functions even if we just have the no_sanitize
> > attribute (without inline mentioned). The same is actually true for
> > KASAN, so KASAN's READ_ONCE_NOCHECK might be broken in a few places,
> > but nobody seems to have noticed [1]. KASAN's __no_kasan_or_inline
> > should also have a 'noinline' I think. I just tested
> > __no_kcsan_or_inline without 'noinline', and yes, GCC 9 still decided
> > to inline a small function and then instrument the accesses.
> >
> > [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59600
> >
> > The good news is that Clang does the right thing when removing
> > 'noinline' from __no_kcsan_or_inline:
> > 1. doesn't inline into functions that are instrumented, and
> > 2. your above example doesn't do the call to __read_once_word_nocheck.
> >
> > The obvious solution to this is: restrict which compiler we want to support?
>
> I would be in favour of that, but I defer to the x86 folks since this
> affects them much more than it does me. On the arm64 side, we've got patches
> queued for 5.8 that require GCC 10.0.1 or later, and that thing is only a
> week old. I think it's reasonable to require a recent toolchain for optional
> features like this that inherently rely on compiler support.
>
> > > > From what I gather, we want to just compile the function as if the
> > > > sanitizer was never enabled. One reason for why this doesn't quite
> > > > work is because of the preprocessor.
> > > >
> > > > Note that the sanitizers won't complain about these accesses, which
> > > > unfortunately is all these attributes ever were documented to do. So
> > > > the attributes aren't completely useless. Why doesn't
> > > > K[AC]SAN_SANITIZE := n work?
> > >
> > > I just don't get the point in having a function annotation if you then have to
> > > pass flags at the per-object level. That also then necessitates either weird
> > > refactoring and grouping of code into "noinstrument.c" type files, or blanket
> > > disabling of instrumentation for things like arch/x86/
> >
> > If you want a solution now, here is one way to get us closer to where
> > we want to be:
> >
> > 1. Peter's patch to add data_race around __READ_ONCE/__WRITE_ONCE.
> > 2. Patch to make __tsan_func_entry/exit disappear with Clang.
> > 3. Remove 'noinline' from __no_kcsan_or_inline.
> > 4. Patch to warn users that KCSAN may have problems with GCC and
> > should use Clang >= 7.
> >
> > But this is probably only half a solution.
>
> At this point, I think that if READ_ONCE_NOCHECK() works as expected, and
> calling __{READ,WRITE}_ONCE from functions tagged with __no_sanitize doesn't
> result in instrumentation, then we're good.

Ouch. With the __{READ,WRITE}_ONCE requirement, we're going to need
Clang 11 though.

Because without the data_race() around __*_ONCE,
arch_atomic_{read,set} will be broken for KCSAN, but we can't have
data_race() because it would still add
kcsan_{enable,disable}_current() calls to __no_sanitize functions (if
compilation unit is instrumented). We can't make arch_atomic functions
__no_sanitize_or_inline, because even in code that we want to
sanitize, they should remain __always_inline (so they work properly in
__no_sanitize functions). Therefore, Clang 11 with support for
distinguishing volatiles will be the compiler that will satisfy all
the constraints.

If this is what we want, let me prepare a series on top of
-tip/locking/kcsan with all the things I think we need.

Thanks,
-- Marco

  reply	other threads:[~2020-05-14  7:32 UTC|newest]

Thread overview: 127+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-11 20:41 Will Deacon
2020-05-11 20:41 ` [PATCH v5 01/18] sparc32: mm: Fix argument checking in __srmmu_get_nocache() Will Deacon
2020-05-12 14:37   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 02/18] sparc32: mm: Restructure sparc32 MMU page-table layout Will Deacon
2020-05-12 14:37   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 03/18] sparc32: mm: Change pgtable_t type to pte_t * instead of struct page * Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 04/18] sparc32: mm: Reduce allocation size for PMD and PTE tables Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-17  0:00   ` [PATCH v5 04/18] " Guenter Roeck
2020-05-17  0:07     ` Guenter Roeck
2020-05-18  8:37       ` Will Deacon
2020-05-18  9:18         ` Mike Rapoport
2020-05-18  9:48         ` Guenter Roeck
2020-05-18 14:23           ` Mike Rapoport
2020-05-18 16:08             ` Guenter Roeck
2020-05-18 18:11               ` Ira Weiny
2020-05-18 18:14               ` Ira Weiny
2020-05-18 18:09             ` Guenter Roeck
2020-05-18 18:21               ` Ira Weiny
2020-05-18 19:15               ` Mike Rapoport
2020-05-19 16:40                 ` Guenter Roeck
2020-05-20 17:03         ` Mike Rapoport
2020-05-20 19:03           ` Guenter Roeck
2020-05-20 19:51             ` Mike Rapoport
2020-05-21 23:02               ` Guenter Roeck
2020-05-24 12:32                 ` Mike Rapoport
2020-05-24 14:01                   ` Guenter Roeck
2020-05-26 13:26                   ` Will Deacon
2020-05-26 14:01                     ` Will Deacon
2020-05-26 15:21                       ` Mike Rapoport
2020-05-26 16:18                       ` Guenter Roeck
2020-05-26 16:29                         ` Mike Rapoport
2020-05-26 17:15                           ` Guenter Roeck
2020-05-11 20:41 ` [PATCH v5 05/18] compiler/gcc: Raise minimum GCC version for kernel builds to 4.8 Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 06/18] netfilter: Avoid assigning 'const' pointer to non-const pointer Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 07/18] net: tls: " Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 08/18] fault_inject: Don't rely on "return value" from WRITE_ONCE() Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 09/18] arm64: csum: Disable KASAN for do_csum() Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 10/18] READ_ONCE: Simplify implementations of {READ,WRITE}_ONCE() Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 11/18] READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 12/18] READ_ONCE: Drop pointer qualifiers when reading from scalar types Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 13/18] locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 14/18] arm64: barrier: Use '__unqual_scalar_typeof' for acquire/release macros Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 15/18] gcov: Remove old GCC 3.4 support Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 16/18] kcsan: Rework data_race() so that it can be used by READ_ONCE() Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 17/18] READ_ONCE: Use data_race() to avoid KCSAN instrumentation Will Deacon
2020-05-12  8:23   ` Peter Zijlstra
2020-05-12  9:49     ` Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-20 22:17     ` Borislav Petkov
2020-05-20 22:30       ` Marco Elver
2020-05-21  7:25         ` Borislav Petkov
2020-05-21  9:37           ` Marco Elver
2020-05-21  3:30       ` Nathan Chancellor
2020-05-22 16:08       ` [tip: locking/kcsan] compiler.h: Avoid nested statement expression in data_race() tip-bot2 for Marco Elver
2020-05-11 20:41 ` [PATCH v5 18/18] linux/compiler.h: Remove redundant '#else' Will Deacon
2020-05-12 14:36   ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-12  8:18 ` [PATCH v5 00/18] Rework READ_ONCE() to improve codegen Peter Zijlstra
2020-05-12 17:53   ` Marco Elver
2020-05-12 18:55     ` Marco Elver
2020-05-12 19:07     ` Peter Zijlstra
2020-05-12 20:31       ` Marco Elver
2020-05-13 11:10         ` Peter Zijlstra
2020-05-13 11:14           ` Peter Zijlstra
2020-05-13 11:48           ` Marco Elver
2020-05-13 12:32             ` Peter Zijlstra
2020-05-13 12:40               ` Will Deacon
2020-05-13 13:15                 ` Marco Elver
2020-05-13 13:24                   ` Peter Zijlstra
2020-05-13 13:58                     ` Marco Elver
2020-05-14 11:21                       ` Peter Zijlstra
2020-05-14 11:24                         ` Peter Zijlstra
2020-05-14 11:35                         ` Peter Zijlstra
2020-05-14 12:01                         ` Will Deacon
2020-05-14 12:27                           ` Peter Zijlstra
2020-05-14 13:07                             ` Marco Elver
2020-05-14 13:14                               ` Peter Zijlstra
2020-05-14 12:20                         ` Peter Zijlstra
2020-05-14 14:13                       ` Peter Zijlstra
2020-05-14 14:20                         ` Marco Elver
2020-05-15  9:20                           ` Peter Zijlstra
2020-05-13 16:50                   ` Will Deacon
2020-05-13 17:32                     ` Marco Elver
2020-05-13 17:47                       ` Will Deacon
2020-05-13 18:54                         ` Marco Elver
2020-05-13 21:25                           ` Will Deacon
2020-05-14  7:31                             ` Marco Elver [this message]
2020-05-14 11:05                               ` Will Deacon
2020-05-14 13:35                                 ` Marco Elver
2020-05-14 13:47                                   ` Peter Zijlstra
2020-05-14 13:50                                   ` Peter Zijlstra
2020-05-14 13:56                                   ` Peter Zijlstra
2020-05-14 14:24                                   ` Peter Zijlstra
2020-05-14 15:09                                     ` Thomas Gleixner
2020-05-14 15:29                                       ` Marco Elver
2020-05-14 19:37                                         ` Thomas Gleixner
2020-05-15 13:55                                     ` David Laight
2020-05-15 14:04                                       ` Marco Elver
2020-05-15 14:07                                       ` Peter Zijlstra
2020-05-14 15:38                                   ` Paul E. McKenney
2020-05-22 16:08                                   ` [tip: locking/kcsan] kcsan: Restrict supported compilers tip-bot2 for Marco Elver
2020-06-03 18:52                                 ` [PATCH v5 00/18] Rework READ_ONCE() to improve codegen Borislav Petkov
2020-06-03 19:23                                   ` Marco Elver
2020-06-03 22:05                                     ` Borislav Petkov
2020-06-08 17:32                                     ` Martin Liška
2020-06-08 19:56                                       ` Marco Elver
2020-06-09 11:55                                         ` Martin Liška
2020-06-09 12:36                                           ` Martin Liška
2020-06-09 13:45                                             ` Marco Elver
2020-05-22 16:08                           ` [tip: locking/kcsan] kcsan: Remove 'noinline' from __no_kcsan_or_inline tip-bot2 for Marco Elver
2020-05-13 13:21                 ` [PATCH v5 00/18] Rework READ_ONCE() to improve codegen David Laight
2020-05-13 16:32                   ` Thomas Gleixner
2020-05-12 21:14       ` Will Deacon
2020-05-12 22:00         ` Marco Elver

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CANpmjNOAi2K6knC9OFUGjpMo-rvtLDzKMb==J=vTRkmaWctFaQ@mail.gmail.com' \
    --to=elver@google.com \
    --cc=dvyukov@google.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=paulmck@kernel.org \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=will@kernel.org \
    --subject='Re: [PATCH v5 00/18] Rework READ_ONCE() to improve codegen' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
on how to clone and mirror all data and code used for this inbox