Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1600848 > unrolled thread

[PATCH 0/3] x86, kasan: add KASAN checks to atomic operations

Back to article view | Back to linux.kernel

Contents

  [PATCH 0/3] x86, kasan: add KASAN checks to atomic operations Dmitry Vyukov <dvyukov@google.com> - 2017-03-14 20:30 +0100
    Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Mark Rutland <mark.rutland@arm.com> - 2017-03-20 18:20 +0100
      Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Mark Rutland <mark.rutland@arm.com> - 2017-03-21 11:50 +0100
        Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Dmitry Vyukov <dvyukov@google.com> - 2017-03-21 19:10 +0100
          Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Arnd Bergmann <arnd@arndb.de> - 2017-03-21 22:30 +0100
            Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Dmitry Vyukov <dvyukov@google.com> - 2017-03-22 11:50 +0100
              Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Arnd Bergmann <arnd@arndb.de> - 2017-03-22 12:40 +0100
                Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Dmitry Vyukov <dvyukov@google.com> - 2017-03-22 13:30 +0100
                  Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Arnd Bergmann <arnd@arndb.de> - 2017-03-22 13:50 +0100
    Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Ingo Molnar <mingo@kernel.org> - 2017-03-24 08:00 +0100
      Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Dmitry Vyukov <dvyukov@google.com> - 2017-03-24 08:20 +0100
        Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Dmitry Vyukov <dvyukov@google.com> - 2017-03-24 09:50 +0100
        Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Ingo Molnar <mingo@kernel.org> - 2017-03-24 12:00 +0100
          Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Dmitry Vyukov <dvyukov@google.com> - 2017-03-24 13:50 +0100
            Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Ingo Molnar <mingo@kernel.org> - 2017-03-28 10:00 +0200
              Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Peter Zijlstra <peterz@infradead.org> - 2017-03-28 11:30 +0200
                Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Dmitry Vyukov <dvyukov@google.com> - 2017-03-28 11:50 +0200
                Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Dmitry Vyukov <dvyukov@google.com> - 2017-03-28 12:00 +0200
                  Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Ingo Molnar <mingo@kernel.org> - 2017-03-28 12:20 +0200
                    Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Dmitry Vyukov <dvyukov@google.com> - 2017-03-28 18:40 +0200
                Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations Ingo Molnar <mingo@kernel.org> - 2017-03-28 12:00 +0200
    Re: [PATCH 0/3] x86, kasan: add KASAN checks to atomic operations Andrew Morton <akpm@linux-foundation.org> - 2017-03-31 00:40 +0200

Page 1 of 2  [1] 2  Next page →

#1600848 — [PATCH 0/3] x86, kasan: add KASAN checks to atomic operations

KASAN uses compiler instrumentation to intercept all memory accesses.
But it does not see memory accesses done in assembly code.
One notable user of assembly code is atomic operations. Frequently,
for example, an atomic reference decrement is the last access to an
object and a good candidate for a racy use-after-free.

Atomic operations are defined in arch files, but KASAN instrumentation
is required for several archs that support KASAN. Later we will need
similar hooks for KMSAN (uninit use detector) and KTSAN (data race
detector).

This change introduces wrappers around atomic operations that can be
used to add KASAN/KMSAN/KTSAN instrumentation across several archs,
and adds KASAN checks to them.

This patch uses the wrappers only for x86 arch. Arm64 will be switched
later. And we also plan to instrument bitops in a similar way.

Within a day it has found its first bug:

BUG: KASAN: use-after-free in atomic_dec_and_test
arch/x86/include/asm/atomic.h:123 [inline] at addr ffff880079c30158
Write of size 4 by task syz-executor6/25698
CPU: 2 PID: 25698 Comm: syz-executor6 Not tainted 4.10.0+ #302
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 kasan_check_write+0x14/0x20 mm/kasan/kasan.c:344
 atomic_dec_and_test arch/x86/include/asm/atomic.h:123 [inline]
 put_task_struct include/linux/sched/task.h:93 [inline]
 put_ctx+0xcf/0x110 kernel/events/core.c:1131
 perf_event_release_kernel+0x3ad/0xc90 kernel/events/core.c:4322
 perf_release+0x37/0x50 kernel/events/core.c:4338
 __fput+0x332/0x800 fs/file_table.c:209
 ____fput+0x15/0x20 fs/file_table.c:245
 task_work_run+0x197/0x260 kernel/task_work.c:116
 exit_task_work include/linux/task_work.h:21 [inline]
 do_exit+0xb38/0x29c0 kernel/exit.c:880
 do_group_exit+0x149/0x420 kernel/exit.c:984
 get_signal+0x7e0/0x1820 kernel/signal.c:2318
 do_signal+0xd2/0x2190 arch/x86/kernel/signal.c:808
 exit_to_usermode_loop+0x200/0x2a0 arch/x86/entry/common.c:157
 syscall_return_slowpath arch/x86/entry/common.c:191 [inline]
 do_syscall_64+0x6fc/0x930 arch/x86/entry/common.c:286
 entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x4458d9
RSP: 002b:00007f3f07187cf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00000000007080c8 RCX: 00000000004458d9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000007080c8
RBP: 00000000007080a8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f3f071889c0 R15: 00007f3f07188700
Object at ffff880079c30140, in cache task_struct size: 5376
Allocated:
PID = 25681
 kmem_cache_alloc_node+0x122/0x6f0 mm/slab.c:3662
 alloc_task_struct_node kernel/fork.c:153 [inline]
 dup_task_struct kernel/fork.c:495 [inline]
 copy_process.part.38+0x19c8/0x4aa0 kernel/fork.c:1560
 copy_process kernel/fork.c:1531 [inline]
 _do_fork+0x200/0x1010 kernel/fork.c:1994
 SYSC_clone kernel/fork.c:2104 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2098
 do_syscall_64+0x2e8/0x930 arch/x86/entry/common.c:281
 return_from_SYSCALL_64+0x0/0x7a
Freed:
PID = 25681
 __cache_free mm/slab.c:3514 [inline]
 kmem_cache_free+0x71/0x240 mm/slab.c:3774
 free_task_struct kernel/fork.c:158 [inline]
 free_task+0x151/0x1d0 kernel/fork.c:370
 copy_process.part.38+0x18e5/0x4aa0 kernel/fork.c:1931
 copy_process kernel/fork.c:1531 [inline]
 _do_fork+0x200/0x1010 kernel/fork.c:1994
 SYSC_clone kernel/fork.c:2104 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2098
 do_syscall_64+0x2e8/0x930 arch/x86/entry/common.c:281
 return_from_SYSCALL_64+0x0/0x7a

Dmitry Vyukov (3):
  kasan: allow kasan_check_read/write() to accept pointers to volatiles
  asm-generic, x86: wrap atomic operations
  asm-generic: add KASAN instrumentation to atomic operations

 arch/x86/include/asm/atomic.h             | 100 ++++++------
 arch/x86/include/asm/atomic64_32.h        |  86 ++++++-----
 arch/x86/include/asm/atomic64_64.h        |  90 +++++------
 arch/x86/include/asm/cmpxchg.h            |  12 +-
 arch/x86/include/asm/cmpxchg_32.h         |   8 +-
 arch/x86/include/asm/cmpxchg_64.h         |   4 +-
 include/asm-generic/atomic-instrumented.h | 246 ++++++++++++++++++++++++++++++
 include/linux/kasan-checks.h              |  10 +-
 mm/kasan/kasan.c                          |   4 +-
 9 files changed, 411 insertions(+), 149 deletions(-)
 create mode 100644 include/asm-generic/atomic-instrumented.h

-- 
2.12.0.367.g23dc2f6d3c-goog

[toc] | [next] | [standalone]

#1604819 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

Hi,

On Tue, Mar 14, 2017 at 08:24:13PM +0100, Dmitry Vyukov wrote:
>  /**
> - * atomic_read - read atomic variable
> + * arch_atomic_read - read atomic variable
>   * @v: pointer of type atomic_t
>   *
>   * Atomically reads the value of @v.
>   */
> -static __always_inline int atomic_read(const atomic_t *v)
> +static __always_inline int arch_atomic_read(const atomic_t *v)
>  {
> -	return READ_ONCE((v)->counter);
> +	/*
> +	 * We use READ_ONCE_NOCHECK() because atomic_read() contains KASAN
> +	 * instrumentation. Double instrumentation is unnecessary.
> +	 */
> +	return READ_ONCE_NOCHECK((v)->counter);
>  }

Just to check, we do this to avoid duplicate reports, right?

If so, double instrumentation isn't solely "unnecessary"; it has a
functional difference, and we should explicitly describe that in the
comment.

... or are duplicate reports supressed somehow?

[...]

> +static __always_inline void arch_atomic_set(atomic_t *v, int i)
>  {
> +	/*
> +	 * We could use WRITE_ONCE_NOCHECK() if it exists, similar to
> +	 * READ_ONCE_NOCHECK() in arch_atomic_read(). But there is no such
> +	 * thing at the moment, and introducing it for this case does not
> +	 * worth it.
> +	 */
>  	WRITE_ONCE(v->counter, i);
>  }

If we are trying to avoid duplicate reports, we should do the same here.

[...]

> +static __always_inline short int atomic_inc_short(short int *v)
> +{
> +	return arch_atomic_inc_short(v);
> +}

This is x86-specific, and AFAICT, not used anywhere.

Given that it is arch-specific, I don't think it should be instrumented
here. If it isn't used, we could get rid of it entirely...

Thanks,
Mark.

[toc] | [prev] | [next] | [standalone]

#1605498 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Tue, Mar 21, 2017 at 12:25:06PM +0300, Andrey Ryabinin wrote:
> On 03/20/2017 08:17 PM, Mark Rutland wrote:
> > Hi,
> > 
> > On Tue, Mar 14, 2017 at 08:24:13PM +0100, Dmitry Vyukov wrote:
> >>  /**
> >> - * atomic_read - read atomic variable
> >> + * arch_atomic_read - read atomic variable
> >>   * @v: pointer of type atomic_t
> >>   *
> >>   * Atomically reads the value of @v.
> >>   */
> >> -static __always_inline int atomic_read(const atomic_t *v)
> >> +static __always_inline int arch_atomic_read(const atomic_t *v)
> >>  {
> >> -	return READ_ONCE((v)->counter);
> >> +	/*
> >> +	 * We use READ_ONCE_NOCHECK() because atomic_read() contains KASAN
> >> +	 * instrumentation. Double instrumentation is unnecessary.
> >> +	 */
> >> +	return READ_ONCE_NOCHECK((v)->counter);
> >>  }
> > 
> > Just to check, we do this to avoid duplicate reports, right?
> > 
> > If so, double instrumentation isn't solely "unnecessary"; it has a
> > functional difference, and we should explicitly describe that in the
> > comment.
> > 
> > ... or are duplicate reports supressed somehow?
> 
> They are not suppressed yet. But I think we should just switch kasan
> to single shot mode, i.e. report only the first error. Single bug
> quite often has multiple invalid memory accesses causing storm in
> dmesg. Also write OOB might corrupt metadata so the next report will
> print bogus alloc/free stacktraces.
> In most cases we need to look only at the first report, so reporting
> anything after the first is just counterproductive.

FWIW, that sounds sane to me.

Given that, I agree with your comment regarding READ_ONCE{,_NOCHECK}().

If anyone really wants all the reports, we could have a boot-time option
to do that.

Thanks,
Mark.

[toc] | [prev] | [next] | [standalone]

#1605866 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Tue, Mar 21, 2017 at 11:41 AM, Mark Rutland <mark.rutland@arm.com> wrote:
> On Tue, Mar 21, 2017 at 12:25:06PM +0300, Andrey Ryabinin wrote:
>> On 03/20/2017 08:17 PM, Mark Rutland wrote:
>> > Hi,
>> >
>> > On Tue, Mar 14, 2017 at 08:24:13PM +0100, Dmitry Vyukov wrote:
>> >>  /**
>> >> - * atomic_read - read atomic variable
>> >> + * arch_atomic_read - read atomic variable
>> >>   * @v: pointer of type atomic_t
>> >>   *
>> >>   * Atomically reads the value of @v.
>> >>   */
>> >> -static __always_inline int atomic_read(const atomic_t *v)
>> >> +static __always_inline int arch_atomic_read(const atomic_t *v)
>> >>  {
>> >> -  return READ_ONCE((v)->counter);
>> >> +  /*
>> >> +   * We use READ_ONCE_NOCHECK() because atomic_read() contains KASAN
>> >> +   * instrumentation. Double instrumentation is unnecessary.
>> >> +   */
>> >> +  return READ_ONCE_NOCHECK((v)->counter);
>> >>  }
>> >
>> > Just to check, we do this to avoid duplicate reports, right?
>> >
>> > If so, double instrumentation isn't solely "unnecessary"; it has a
>> > functional difference, and we should explicitly describe that in the
>> > comment.
>> >
>> > ... or are duplicate reports supressed somehow?
>>
>> They are not suppressed yet. But I think we should just switch kasan
>> to single shot mode, i.e. report only the first error. Single bug
>> quite often has multiple invalid memory accesses causing storm in
>> dmesg. Also write OOB might corrupt metadata so the next report will
>> print bogus alloc/free stacktraces.
>> In most cases we need to look only at the first report, so reporting
>> anything after the first is just counterproductive.
>
> FWIW, that sounds sane to me.
>
> Given that, I agree with your comment regarding READ_ONCE{,_NOCHECK}().
>
> If anyone really wants all the reports, we could have a boot-time option
> to do that.


I don't mind changing READ_ONCE_NOCHECK to READ_ONCE. But I don't have
strong preference either way.

We could do:
#define arch_atomic_read_is_already_instrumented 1
and then skip instrumentation in asm-generic if it's defined. But I
don't think it's worth it.

There is no functional difference, it's only an optimization (now
somewhat questionable). As Andrey said, one can get a splash of
reports anyway, and it's the first one that is important. We use KASAN
with panic_on_warn=1 so we don't even see the rest.

[toc] | [prev] | [next] | [standalone]

#1606009 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Tue, Mar 21, 2017 at 7:06 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Tue, Mar 21, 2017 at 11:41 AM, Mark Rutland <mark.rutland@arm.com> wrote:
>> On Tue, Mar 21, 2017 at 12:25:06PM +0300, Andrey Ryabinin wrote:
>
> I don't mind changing READ_ONCE_NOCHECK to READ_ONCE. But I don't have
> strong preference either way.
>
> We could do:
> #define arch_atomic_read_is_already_instrumented 1
> and then skip instrumentation in asm-generic if it's defined. But I
> don't think it's worth it.
>
> There is no functional difference, it's only an optimization (now
> somewhat questionable). As Andrey said, one can get a splash of
> reports anyway, and it's the first one that is important. We use KASAN
> with panic_on_warn=1 so we don't even see the rest.

I'm getting couple of new stack size warnings that are all the result
of the _NOCHECK.

/git/arm-soc/mm/page_alloc.c: In function 'show_free_areas':
/git/arm-soc/mm/page_alloc.c:4685:1: error: the frame size of 3368
bytes is larger than 3072 bytes [-Werror=frame-larger-than=]
 }
/git/arm-soc/lib/atomic64_test.c: In function 'test_atomic':
/git/arm-soc/lib/atomic64_test.c:148:1: error: the frame size of 6528
bytes is larger than 3072 bytes [-Werror=frame-larger-than=]
 }
 ^
/git/arm-soc/lib/atomic64_test.c: In function 'test_atomic64':
/git/arm-soc/lib/atomic64_test.c:243:1: error: the frame size of 7112
bytes is larger than 3072 bytes [-Werror=frame-larger-than=]

This is with my previous set of patches already applied, so
READ_ONCE should not cause problems. Reverting
the READ_ONCE_NOCHECK() in atomic_read() and atomic64_read()
back to READ_ONCE()

I also get a build failure as a result of your patch, but this one is
not addressed by using READ_ONCE():

In file included from /git/arm-soc/arch/x86/include/asm/atomic.h:7:0,
                 from /git/arm-soc/include/linux/atomic.h:4,
                 from /git/arm-soc/arch/x86/include/asm/thread_info.h:53,
                 from /git/arm-soc/include/linux/thread_info.h:25,
                 from /git/arm-soc/arch/x86/include/asm/preempt.h:6,
                 from /git/arm-soc/include/linux/preempt.h:80,
                 from /git/arm-soc/include/linux/spinlock.h:50,
                 from /git/arm-soc/include/linux/mmzone.h:7,
                 from /git/arm-soc/include/linux/gfp.h:5,
                 from /git/arm-soc/include/linux/mm.h:9,
                 from /git/arm-soc/mm/slub.c:12:
/git/arm-soc/mm/slub.c: In function '__slab_free':
/git/arm-soc/arch/x86/include/asm/cmpxchg.h:174:2: error: 'asm'
operand has impossible constraints
  asm volatile(pfx "cmpxchg%c4b %2; sete %0"   \
  ^
/git/arm-soc/arch/x86/include/asm/cmpxchg.h:183:2: note: in expansion
of macro '__cmpxchg_double'
  __cmpxchg_double(LOCK_PREFIX, p1, p2, o1, o2, n1, n2)
  ^~~~~~~~~~~~~~~~
/git/arm-soc/include/asm-generic/atomic-instrumented.h:236:2: note: in
expansion of macro 'arch_cmpxchg_double'
  arch_cmpxchg_double(____p1, (p2), (o1), (o2), (n1), (n2)); \
  ^~~~~~~~~~~~~~~~~~~
/git/arm-soc/mm/slub.c:385:7: note: in expansion of macro 'cmpxchg_double'
   if (cmpxchg_double(&page->freelist, &page->counters,
       ^~~~~~~~~~~~~~
/git/arm-soc/scripts/Makefile.build:308: recipe for target 'mm/slub.o' failed

http://pastebin.com/raw/qXVpi9Ev has the defconfig file I used, and I get the
error with any gcc version I tried (4.9 through 7.0.1).

      Arnd

[toc] | [prev] | [next] | [standalone]

#1606355 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Tue, Mar 21, 2017 at 10:20 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Tue, Mar 21, 2017 at 7:06 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
>> On Tue, Mar 21, 2017 at 11:41 AM, Mark Rutland <mark.rutland@arm.com> wrote:
>>> On Tue, Mar 21, 2017 at 12:25:06PM +0300, Andrey Ryabinin wrote:
>>
>> I don't mind changing READ_ONCE_NOCHECK to READ_ONCE. But I don't have
>> strong preference either way.
>>
>> We could do:
>> #define arch_atomic_read_is_already_instrumented 1
>> and then skip instrumentation in asm-generic if it's defined. But I
>> don't think it's worth it.
>>
>> There is no functional difference, it's only an optimization (now
>> somewhat questionable). As Andrey said, one can get a splash of
>> reports anyway, and it's the first one that is important. We use KASAN
>> with panic_on_warn=1 so we don't even see the rest.
>
> I'm getting couple of new stack size warnings that are all the result
> of the _NOCHECK.
>
> /git/arm-soc/mm/page_alloc.c: In function 'show_free_areas':
> /git/arm-soc/mm/page_alloc.c:4685:1: error: the frame size of 3368
> bytes is larger than 3072 bytes [-Werror=frame-larger-than=]
>  }
> /git/arm-soc/lib/atomic64_test.c: In function 'test_atomic':
> /git/arm-soc/lib/atomic64_test.c:148:1: error: the frame size of 6528
> bytes is larger than 3072 bytes [-Werror=frame-larger-than=]
>  }
>  ^
> /git/arm-soc/lib/atomic64_test.c: In function 'test_atomic64':
> /git/arm-soc/lib/atomic64_test.c:243:1: error: the frame size of 7112
> bytes is larger than 3072 bytes [-Werror=frame-larger-than=]
>
> This is with my previous set of patches already applied, so
> READ_ONCE should not cause problems. Reverting
> the READ_ONCE_NOCHECK() in atomic_read() and atomic64_read()
> back to READ_ONCE()
>
> I also get a build failure as a result of your patch, but this one is
> not addressed by using READ_ONCE():
>
> In file included from /git/arm-soc/arch/x86/include/asm/atomic.h:7:0,
>                  from /git/arm-soc/include/linux/atomic.h:4,
>                  from /git/arm-soc/arch/x86/include/asm/thread_info.h:53,
>                  from /git/arm-soc/include/linux/thread_info.h:25,
>                  from /git/arm-soc/arch/x86/include/asm/preempt.h:6,
>                  from /git/arm-soc/include/linux/preempt.h:80,
>                  from /git/arm-soc/include/linux/spinlock.h:50,
>                  from /git/arm-soc/include/linux/mmzone.h:7,
>                  from /git/arm-soc/include/linux/gfp.h:5,
>                  from /git/arm-soc/include/linux/mm.h:9,
>                  from /git/arm-soc/mm/slub.c:12:
> /git/arm-soc/mm/slub.c: In function '__slab_free':
> /git/arm-soc/arch/x86/include/asm/cmpxchg.h:174:2: error: 'asm'
> operand has impossible constraints
>   asm volatile(pfx "cmpxchg%c4b %2; sete %0"   \
>   ^
> /git/arm-soc/arch/x86/include/asm/cmpxchg.h:183:2: note: in expansion
> of macro '__cmpxchg_double'
>   __cmpxchg_double(LOCK_PREFIX, p1, p2, o1, o2, n1, n2)
>   ^~~~~~~~~~~~~~~~
> /git/arm-soc/include/asm-generic/atomic-instrumented.h:236:2: note: in
> expansion of macro 'arch_cmpxchg_double'
>   arch_cmpxchg_double(____p1, (p2), (o1), (o2), (n1), (n2)); \
>   ^~~~~~~~~~~~~~~~~~~
> /git/arm-soc/mm/slub.c:385:7: note: in expansion of macro 'cmpxchg_double'
>    if (cmpxchg_double(&page->freelist, &page->counters,
>        ^~~~~~~~~~~~~~
> /git/arm-soc/scripts/Makefile.build:308: recipe for target 'mm/slub.o' failed
>
> http://pastebin.com/raw/qXVpi9Ev has the defconfig file I used, and I get the
> error with any gcc version I tried (4.9 through 7.0.1).


Initially I've tested with my stock gcc 4.8.4 (Ubuntu
4.8.4-2ubuntu1~14.04.3) and amusingly it works. But I can reproduce
the bug with 7.0.1.
Filed https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80148
Will think about kernel fix.
Thanks!

[toc] | [prev] | [next] | [standalone]

#1606394 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Wed, Mar 22, 2017 at 11:42 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Tue, Mar 21, 2017 at 10:20 PM, Arnd Bergmann <arnd@arndb.de> wrote:
>> On Tue, Mar 21, 2017 at 7:06 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
>
> Initially I've tested with my stock gcc 4.8.4 (Ubuntu
> 4.8.4-2ubuntu1~14.04.3) and amusingly it works. But I can reproduce
> the bug with 7.0.1.

It's probably because gcc-4.8 didn't support KASAN yet, so the added
check had no effect.

      Arnd

[toc] | [prev] | [next] | [standalone]

#1606416 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Wed, Mar 22, 2017 at 12:30 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Wed, Mar 22, 2017 at 11:42 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
>> On Tue, Mar 21, 2017 at 10:20 PM, Arnd Bergmann <arnd@arndb.de> wrote:
>>> On Tue, Mar 21, 2017 at 7:06 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
>>
>> Initially I've tested with my stock gcc 4.8.4 (Ubuntu
>> 4.8.4-2ubuntu1~14.04.3) and amusingly it works. But I can reproduce
>> the bug with 7.0.1.
>
> It's probably because gcc-4.8 didn't support KASAN yet, so the added
> check had no effect.

I've tested without KASAN with both compilers.

[toc] | [prev] | [next] | [standalone]

#1606437 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Wed, Mar 22, 2017 at 1:14 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Wed, Mar 22, 2017 at 12:30 PM, Arnd Bergmann <arnd@arndb.de> wrote:
>> On Wed, Mar 22, 2017 at 11:42 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
>>> On Tue, Mar 21, 2017 at 10:20 PM, Arnd Bergmann <arnd@arndb.de> wrote:
>>>> On Tue, Mar 21, 2017 at 7:06 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
>>>
>>> Initially I've tested with my stock gcc 4.8.4 (Ubuntu
>>> 4.8.4-2ubuntu1~14.04.3) and amusingly it works. But I can reproduce
>>> the bug with 7.0.1.
>>
>> It's probably because gcc-4.8 didn't support KASAN yet, so the added
>> check had no effect.
>
> I've tested without KASAN with both compilers.

Ah ok. I had not realized that this happened even without KASAN. I only saw this
problem in one out of hundreds of defconfig builds and assumed it was related
since this came from a kasan change.

      Arnd

[toc] | [prev] | [next] | [standalone]

#1608165 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

* Dmitry Vyukov <dvyukov@google.com> wrote:

> KASAN uses compiler instrumentation to intercept all memory accesses.
> But it does not see memory accesses done in assembly code.
> One notable user of assembly code is atomic operations. Frequently,
> for example, an atomic reference decrement is the last access to an
> object and a good candidate for a racy use-after-free.
> 
> Atomic operations are defined in arch files, but KASAN instrumentation
> is required for several archs that support KASAN. Later we will need
> similar hooks for KMSAN (uninit use detector) and KTSAN (data race
> detector).
> 
> This change introduces wrappers around atomic operations that can be
> used to add KASAN/KMSAN/KTSAN instrumentation across several archs.
> This patch uses the wrappers only for x86 arch. Arm64 will be switched
> later.
> 
> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Will Deacon <will.deacon@arm.com>,
> Cc: Andrew Morton <akpm@linux-foundation.org>,
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
> Cc: Ingo Molnar <mingo@redhat.com>,
> Cc: kasan-dev@googlegroups.com
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Cc: x86@kernel.org
> ---
>  arch/x86/include/asm/atomic.h             | 100 +++++++-------
>  arch/x86/include/asm/atomic64_32.h        |  86 ++++++------
>  arch/x86/include/asm/atomic64_64.h        |  90 ++++++-------
>  arch/x86/include/asm/cmpxchg.h            |  12 +-
>  arch/x86/include/asm/cmpxchg_32.h         |   8 +-
>  arch/x86/include/asm/cmpxchg_64.h         |   4 +-
>  include/asm-generic/atomic-instrumented.h | 210 ++++++++++++++++++++++++++++++
>  7 files changed, 367 insertions(+), 143 deletions(-)

Ugh, that's disgusting really...

> 
> diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h
> index 14635c5ea025..95dd167eb3af 100644
> --- a/arch/x86/include/asm/atomic.h
> +++ b/arch/x86/include/asm/atomic.h
> @@ -16,36 +16,46 @@
>  #define ATOMIC_INIT(i)	{ (i) }
>  
>  /**
> - * atomic_read - read atomic variable
> + * arch_atomic_read - read atomic variable
>   * @v: pointer of type atomic_t
>   *
>   * Atomically reads the value of @v.
>   */
> -static __always_inline int atomic_read(const atomic_t *v)
> +static __always_inline int arch_atomic_read(const atomic_t *v)
>  {
> -	return READ_ONCE((v)->counter);
> +	/*
> +	 * We use READ_ONCE_NOCHECK() because atomic_read() contains KASAN
> +	 * instrumentation. Double instrumentation is unnecessary.
> +	 */
> +	return READ_ONCE_NOCHECK((v)->counter);
>  }

Firstly, the patch is way too large, please split off new the documentation parts 
of the patch to reduce the size and to make it easier to read!

Secondly, the next patch should do the rename to arch_atomic_*() pattern - and 
nothing else:

>  
>  /**
> - * atomic_set - set atomic variable
> + * arch_atomic_set - set atomic variable
>   * @v: pointer of type atomic_t
>   * @i: required value
>   *
>   * Atomically sets the value of @v to @i.
>   */
> -static __always_inline void atomic_set(atomic_t *v, int i)
> +static __always_inline void arch_atomic_set(atomic_t *v, int i)


Third, the prototype CPP complications:

> +#define __INSTR_VOID1(op, sz)						\
> +static __always_inline void atomic##sz##_##op(atomic##sz##_t *v)	\
> +{									\
> +	arch_atomic##sz##_##op(v);					\
> +}
> +
> +#define INSTR_VOID1(op)	\
> +__INSTR_VOID1(op,);	\
> +__INSTR_VOID1(op, 64)
> +
> +INSTR_VOID1(inc);
> +INSTR_VOID1(dec);
> +
> +#undef __INSTR_VOID1
> +#undef INSTR_VOID1
> +
> +#define __INSTR_VOID2(op, sz, type)					\
> +static __always_inline void atomic##sz##_##op(type i, atomic##sz##_t *v)\
> +{									\
> +	arch_atomic##sz##_##op(i, v);					\
> +}
> +
> +#define INSTR_VOID2(op)		\
> +__INSTR_VOID2(op, , int);	\
> +__INSTR_VOID2(op, 64, long long)
> +
> +INSTR_VOID2(add);
> +INSTR_VOID2(sub);
> +INSTR_VOID2(and);
> +INSTR_VOID2(or);
> +INSTR_VOID2(xor);
> +
> +#undef __INSTR_VOID2
> +#undef INSTR_VOID2
> +
> +#define __INSTR_RET1(op, sz, type, rtype)				\
> +static __always_inline rtype atomic##sz##_##op(atomic##sz##_t *v)	\
> +{									\
> +	return arch_atomic##sz##_##op(v);				\
> +}
> +
> +#define INSTR_RET1(op)		\
> +__INSTR_RET1(op, , int, int);	\
> +__INSTR_RET1(op, 64, long long, long long)
> +
> +INSTR_RET1(inc_return);
> +INSTR_RET1(dec_return);
> +__INSTR_RET1(inc_not_zero, 64, long long, long long);
> +__INSTR_RET1(dec_if_positive, 64, long long, long long);
> +
> +#define INSTR_RET_BOOL1(op)	\
> +__INSTR_RET1(op, , int, bool);	\
> +__INSTR_RET1(op, 64, long long, bool)
> +
> +INSTR_RET_BOOL1(dec_and_test);
> +INSTR_RET_BOOL1(inc_and_test);
> +
> +#undef __INSTR_RET1
> +#undef INSTR_RET1
> +#undef INSTR_RET_BOOL1
> +
> +#define __INSTR_RET2(op, sz, type, rtype)				\
> +static __always_inline rtype atomic##sz##_##op(type i, atomic##sz##_t *v) \
> +{									\
> +	return arch_atomic##sz##_##op(i, v);				\
> +}
> +
> +#define INSTR_RET2(op)		\
> +__INSTR_RET2(op, , int, int);	\
> +__INSTR_RET2(op, 64, long long, long long)
> +
> +INSTR_RET2(add_return);
> +INSTR_RET2(sub_return);
> +INSTR_RET2(fetch_add);
> +INSTR_RET2(fetch_sub);
> +INSTR_RET2(fetch_and);
> +INSTR_RET2(fetch_or);
> +INSTR_RET2(fetch_xor);
> +
> +#define INSTR_RET_BOOL2(op)		\
> +__INSTR_RET2(op, , int, bool);		\
> +__INSTR_RET2(op, 64, long long, bool)
> +
> +INSTR_RET_BOOL2(sub_and_test);
> +INSTR_RET_BOOL2(add_negative);
> +
> +#undef __INSTR_RET2
> +#undef INSTR_RET2
> +#undef INSTR_RET_BOOL2

Are just utterly disgusting that turn perfectly readable code into an unreadable, 
unmaintainable mess.

You need to find some better, cleaner solution please, or convince me that no such 
solution is possible. NAK for the time being.

Thanks,

	Ingo

[toc] | [prev] | [next] | [standalone]

#1608172 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Fri, Mar 24, 2017 at 7:52 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Dmitry Vyukov <dvyukov@google.com> wrote:
>
>> KASAN uses compiler instrumentation to intercept all memory accesses.
>> But it does not see memory accesses done in assembly code.
>> One notable user of assembly code is atomic operations. Frequently,
>> for example, an atomic reference decrement is the last access to an
>> object and a good candidate for a racy use-after-free.
>>
>> Atomic operations are defined in arch files, but KASAN instrumentation
>> is required for several archs that support KASAN. Later we will need
>> similar hooks for KMSAN (uninit use detector) and KTSAN (data race
>> detector).
>>
>> This change introduces wrappers around atomic operations that can be
>> used to add KASAN/KMSAN/KTSAN instrumentation across several archs.
>> This patch uses the wrappers only for x86 arch. Arm64 will be switched
>> later.
>>
>> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Will Deacon <will.deacon@arm.com>,
>> Cc: Andrew Morton <akpm@linux-foundation.org>,
>> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
>> Cc: Ingo Molnar <mingo@redhat.com>,
>> Cc: kasan-dev@googlegroups.com
>> Cc: linux-mm@kvack.org
>> Cc: linux-kernel@vger.kernel.org
>> Cc: x86@kernel.org
>> ---
>>  arch/x86/include/asm/atomic.h             | 100 +++++++-------
>>  arch/x86/include/asm/atomic64_32.h        |  86 ++++++------
>>  arch/x86/include/asm/atomic64_64.h        |  90 ++++++-------
>>  arch/x86/include/asm/cmpxchg.h            |  12 +-
>>  arch/x86/include/asm/cmpxchg_32.h         |   8 +-
>>  arch/x86/include/asm/cmpxchg_64.h         |   4 +-
>>  include/asm-generic/atomic-instrumented.h | 210 ++++++++++++++++++++++++++++++
>>  7 files changed, 367 insertions(+), 143 deletions(-)
>
> Ugh, that's disgusting really...
>
>>
>> diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h
>> index 14635c5ea025..95dd167eb3af 100644
>> --- a/arch/x86/include/asm/atomic.h
>> +++ b/arch/x86/include/asm/atomic.h
>> @@ -16,36 +16,46 @@
>>  #define ATOMIC_INIT(i)       { (i) }
>>
>>  /**
>> - * atomic_read - read atomic variable
>> + * arch_atomic_read - read atomic variable
>>   * @v: pointer of type atomic_t
>>   *
>>   * Atomically reads the value of @v.
>>   */
>> -static __always_inline int atomic_read(const atomic_t *v)
>> +static __always_inline int arch_atomic_read(const atomic_t *v)
>>  {
>> -     return READ_ONCE((v)->counter);
>> +     /*
>> +      * We use READ_ONCE_NOCHECK() because atomic_read() contains KASAN
>> +      * instrumentation. Double instrumentation is unnecessary.
>> +      */
>> +     return READ_ONCE_NOCHECK((v)->counter);
>>  }

Hello Ingo,

> Firstly, the patch is way too large, please split off new the documentation parts
> of the patch to reduce the size and to make it easier to read!
>
> Secondly, the next patch should do the rename to arch_atomic_*() pattern - and
> nothing else:

Next after what? Please provide full list of patches as you see them.
How do we avoid build breakage if we do only the rename in a separate patch?



>>  /**
>> - * atomic_set - set atomic variable
>> + * arch_atomic_set - set atomic variable
>>   * @v: pointer of type atomic_t
>>   * @i: required value
>>   *
>>   * Atomically sets the value of @v to @i.
>>   */
>> -static __always_inline void atomic_set(atomic_t *v, int i)
>> +static __always_inline void arch_atomic_set(atomic_t *v, int i)
>
>
> Third, the prototype CPP complications:
>
>> +#define __INSTR_VOID1(op, sz)                                                \
>> +static __always_inline void atomic##sz##_##op(atomic##sz##_t *v)     \
>> +{                                                                    \
>> +     arch_atomic##sz##_##op(v);                                      \
>> +}
>> +
>> +#define INSTR_VOID1(op)      \
>> +__INSTR_VOID1(op,);  \
>> +__INSTR_VOID1(op, 64)
>> +
>> +INSTR_VOID1(inc);
>> +INSTR_VOID1(dec);
>> +
>> +#undef __INSTR_VOID1
>> +#undef INSTR_VOID1
>> +
>> +#define __INSTR_VOID2(op, sz, type)                                  \
>> +static __always_inline void atomic##sz##_##op(type i, atomic##sz##_t *v)\
>> +{                                                                    \
>> +     arch_atomic##sz##_##op(i, v);                                   \
>> +}
>> +
>> +#define INSTR_VOID2(op)              \
>> +__INSTR_VOID2(op, , int);    \
>> +__INSTR_VOID2(op, 64, long long)
>> +
>> +INSTR_VOID2(add);
>> +INSTR_VOID2(sub);
>> +INSTR_VOID2(and);
>> +INSTR_VOID2(or);
>> +INSTR_VOID2(xor);
>> +
>> +#undef __INSTR_VOID2
>> +#undef INSTR_VOID2
>> +
>> +#define __INSTR_RET1(op, sz, type, rtype)                            \
>> +static __always_inline rtype atomic##sz##_##op(atomic##sz##_t *v)    \
>> +{                                                                    \
>> +     return arch_atomic##sz##_##op(v);                               \
>> +}
>> +
>> +#define INSTR_RET1(op)               \
>> +__INSTR_RET1(op, , int, int);        \
>> +__INSTR_RET1(op, 64, long long, long long)
>> +
>> +INSTR_RET1(inc_return);
>> +INSTR_RET1(dec_return);
>> +__INSTR_RET1(inc_not_zero, 64, long long, long long);
>> +__INSTR_RET1(dec_if_positive, 64, long long, long long);
>> +
>> +#define INSTR_RET_BOOL1(op)  \
>> +__INSTR_RET1(op, , int, bool);       \
>> +__INSTR_RET1(op, 64, long long, bool)
>> +
>> +INSTR_RET_BOOL1(dec_and_test);
>> +INSTR_RET_BOOL1(inc_and_test);
>> +
>> +#undef __INSTR_RET1
>> +#undef INSTR_RET1
>> +#undef INSTR_RET_BOOL1
>> +
>> +#define __INSTR_RET2(op, sz, type, rtype)                            \
>> +static __always_inline rtype atomic##sz##_##op(type i, atomic##sz##_t *v) \
>> +{                                                                    \
>> +     return arch_atomic##sz##_##op(i, v);                            \
>> +}
>> +
>> +#define INSTR_RET2(op)               \
>> +__INSTR_RET2(op, , int, int);        \
>> +__INSTR_RET2(op, 64, long long, long long)
>> +
>> +INSTR_RET2(add_return);
>> +INSTR_RET2(sub_return);
>> +INSTR_RET2(fetch_add);
>> +INSTR_RET2(fetch_sub);
>> +INSTR_RET2(fetch_and);
>> +INSTR_RET2(fetch_or);
>> +INSTR_RET2(fetch_xor);
>> +
>> +#define INSTR_RET_BOOL2(op)          \
>> +__INSTR_RET2(op, , int, bool);               \
>> +__INSTR_RET2(op, 64, long long, bool)
>> +
>> +INSTR_RET_BOOL2(sub_and_test);
>> +INSTR_RET_BOOL2(add_negative);
>> +
>> +#undef __INSTR_RET2
>> +#undef INSTR_RET2
>> +#undef INSTR_RET_BOOL2
>
> Are just utterly disgusting that turn perfectly readable code into an unreadable,
> unmaintainable mess.
>
> You need to find some better, cleaner solution please, or convince me that no such
> solution is possible. NAK for the time being.

Well, I can just write all functions as is. Does it better confirm to
kernel style? I've just looked at the x86 atomic.h and it uses macros
for similar purpose (ATOMIC_OP/ATOMIC_FETCH_OP), so I thought that
must be idiomatic kernel style...

[toc] | [prev] | [next] | [standalone]

#1608230 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Fri, Mar 24, 2017 at 8:14 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Fri, Mar 24, 2017 at 7:52 AM, Ingo Molnar <mingo@kernel.org> wrote:
>>
>> * Dmitry Vyukov <dvyukov@google.com> wrote:
>>
>>> KASAN uses compiler instrumentation to intercept all memory accesses.
>>> But it does not see memory accesses done in assembly code.
>>> One notable user of assembly code is atomic operations. Frequently,
>>> for example, an atomic reference decrement is the last access to an
>>> object and a good candidate for a racy use-after-free.
>>>
>>> Atomic operations are defined in arch files, but KASAN instrumentation
>>> is required for several archs that support KASAN. Later we will need
>>> similar hooks for KMSAN (uninit use detector) and KTSAN (data race
>>> detector).
>>>
>>> This change introduces wrappers around atomic operations that can be
>>> used to add KASAN/KMSAN/KTSAN instrumentation across several archs.
>>> This patch uses the wrappers only for x86 arch. Arm64 will be switched
>>> later.
>>>
>>> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
>>> Cc: Mark Rutland <mark.rutland@arm.com>
>>> Cc: Peter Zijlstra <peterz@infradead.org>
>>> Cc: Will Deacon <will.deacon@arm.com>,
>>> Cc: Andrew Morton <akpm@linux-foundation.org>,
>>> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
>>> Cc: Ingo Molnar <mingo@redhat.com>,
>>> Cc: kasan-dev@googlegroups.com
>>> Cc: linux-mm@kvack.org
>>> Cc: linux-kernel@vger.kernel.org
>>> Cc: x86@kernel.org
>>> ---
>>>  arch/x86/include/asm/atomic.h             | 100 +++++++-------
>>>  arch/x86/include/asm/atomic64_32.h        |  86 ++++++------
>>>  arch/x86/include/asm/atomic64_64.h        |  90 ++++++-------
>>>  arch/x86/include/asm/cmpxchg.h            |  12 +-
>>>  arch/x86/include/asm/cmpxchg_32.h         |   8 +-
>>>  arch/x86/include/asm/cmpxchg_64.h         |   4 +-
>>>  include/asm-generic/atomic-instrumented.h | 210 ++++++++++++++++++++++++++++++
>>>  7 files changed, 367 insertions(+), 143 deletions(-)
>>
>> Ugh, that's disgusting really...
>>
>>>
>>> diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h
>>> index 14635c5ea025..95dd167eb3af 100644
>>> --- a/arch/x86/include/asm/atomic.h
>>> +++ b/arch/x86/include/asm/atomic.h
>>> @@ -16,36 +16,46 @@
>>>  #define ATOMIC_INIT(i)       { (i) }
>>>
>>>  /**
>>> - * atomic_read - read atomic variable
>>> + * arch_atomic_read - read atomic variable
>>>   * @v: pointer of type atomic_t
>>>   *
>>>   * Atomically reads the value of @v.
>>>   */
>>> -static __always_inline int atomic_read(const atomic_t *v)
>>> +static __always_inline int arch_atomic_read(const atomic_t *v)
>>>  {
>>> -     return READ_ONCE((v)->counter);
>>> +     /*
>>> +      * We use READ_ONCE_NOCHECK() because atomic_read() contains KASAN
>>> +      * instrumentation. Double instrumentation is unnecessary.
>>> +      */
>>> +     return READ_ONCE_NOCHECK((v)->counter);
>>>  }
>
> Hello Ingo,
>
>> Firstly, the patch is way too large, please split off new the documentation parts
>> of the patch to reduce the size and to make it easier to read!
>>
>> Secondly, the next patch should do the rename to arch_atomic_*() pattern - and
>> nothing else:
>
> Next after what? Please provide full list of patches as you see them.
> How do we avoid build breakage if we do only the rename in a separate patch?
>
>
>
>>>  /**
>>> - * atomic_set - set atomic variable
>>> + * arch_atomic_set - set atomic variable
>>>   * @v: pointer of type atomic_t
>>>   * @i: required value
>>>   *
>>>   * Atomically sets the value of @v to @i.
>>>   */
>>> -static __always_inline void atomic_set(atomic_t *v, int i)
>>> +static __always_inline void arch_atomic_set(atomic_t *v, int i)
>>
>>
>> Third, the prototype CPP complications:
>>
>>> +#define __INSTR_VOID1(op, sz)                                                \
>>> +static __always_inline void atomic##sz##_##op(atomic##sz##_t *v)     \
>>> +{                                                                    \
>>> +     arch_atomic##sz##_##op(v);                                      \
>>> +}
>>> +
>>> +#define INSTR_VOID1(op)      \
>>> +__INSTR_VOID1(op,);  \
>>> +__INSTR_VOID1(op, 64)
>>> +
>>> +INSTR_VOID1(inc);
>>> +INSTR_VOID1(dec);
>>> +
>>> +#undef __INSTR_VOID1
>>> +#undef INSTR_VOID1
>>> +
>>> +#define __INSTR_VOID2(op, sz, type)                                  \
>>> +static __always_inline void atomic##sz##_##op(type i, atomic##sz##_t *v)\
>>> +{                                                                    \
>>> +     arch_atomic##sz##_##op(i, v);                                   \
>>> +}
>>> +
>>> +#define INSTR_VOID2(op)              \
>>> +__INSTR_VOID2(op, , int);    \
>>> +__INSTR_VOID2(op, 64, long long)
>>> +
>>> +INSTR_VOID2(add);
>>> +INSTR_VOID2(sub);
>>> +INSTR_VOID2(and);
>>> +INSTR_VOID2(or);
>>> +INSTR_VOID2(xor);
>>> +
>>> +#undef __INSTR_VOID2
>>> +#undef INSTR_VOID2
>>> +
>>> +#define __INSTR_RET1(op, sz, type, rtype)                            \
>>> +static __always_inline rtype atomic##sz##_##op(atomic##sz##_t *v)    \
>>> +{                                                                    \
>>> +     return arch_atomic##sz##_##op(v);                               \
>>> +}
>>> +
>>> +#define INSTR_RET1(op)               \
>>> +__INSTR_RET1(op, , int, int);        \
>>> +__INSTR_RET1(op, 64, long long, long long)
>>> +
>>> +INSTR_RET1(inc_return);
>>> +INSTR_RET1(dec_return);
>>> +__INSTR_RET1(inc_not_zero, 64, long long, long long);
>>> +__INSTR_RET1(dec_if_positive, 64, long long, long long);
>>> +
>>> +#define INSTR_RET_BOOL1(op)  \
>>> +__INSTR_RET1(op, , int, bool);       \
>>> +__INSTR_RET1(op, 64, long long, bool)
>>> +
>>> +INSTR_RET_BOOL1(dec_and_test);
>>> +INSTR_RET_BOOL1(inc_and_test);
>>> +
>>> +#undef __INSTR_RET1
>>> +#undef INSTR_RET1
>>> +#undef INSTR_RET_BOOL1
>>> +
>>> +#define __INSTR_RET2(op, sz, type, rtype)                            \
>>> +static __always_inline rtype atomic##sz##_##op(type i, atomic##sz##_t *v) \
>>> +{                                                                    \
>>> +     return arch_atomic##sz##_##op(i, v);                            \
>>> +}
>>> +
>>> +#define INSTR_RET2(op)               \
>>> +__INSTR_RET2(op, , int, int);        \
>>> +__INSTR_RET2(op, 64, long long, long long)
>>> +
>>> +INSTR_RET2(add_return);
>>> +INSTR_RET2(sub_return);
>>> +INSTR_RET2(fetch_add);
>>> +INSTR_RET2(fetch_sub);
>>> +INSTR_RET2(fetch_and);
>>> +INSTR_RET2(fetch_or);
>>> +INSTR_RET2(fetch_xor);
>>> +
>>> +#define INSTR_RET_BOOL2(op)          \
>>> +__INSTR_RET2(op, , int, bool);               \
>>> +__INSTR_RET2(op, 64, long long, bool)
>>> +
>>> +INSTR_RET_BOOL2(sub_and_test);
>>> +INSTR_RET_BOOL2(add_negative);
>>> +
>>> +#undef __INSTR_RET2
>>> +#undef INSTR_RET2
>>> +#undef INSTR_RET_BOOL2
>>
>> Are just utterly disgusting that turn perfectly readable code into an unreadable,
>> unmaintainable mess.
>>
>> You need to find some better, cleaner solution please, or convince me that no such
>> solution is possible. NAK for the time being.
>
> Well, I can just write all functions as is. Does it better confirm to
> kernel style? I've just looked at the x86 atomic.h and it uses macros
> for similar purpose (ATOMIC_OP/ATOMIC_FETCH_OP), so I thought that
> must be idiomatic kernel style...


Stephen Rothwell reported that this patch conflicts with:
  a9ebf306f52c ("locking/atomic: Introduce atomic_try_cmpxchg()")
  e6790e4b5d5e ("locking/atomic/x86: Use atomic_try_cmpxchg()")
does it make sense to base my patch on the tree where these patches
were added and then submit to that tree?

I've also sent 2 fixes for this patch, if I resent this I also squash
these fixes, right?

[toc] | [prev] | [next] | [standalone]

#1608314 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

* Dmitry Vyukov <dvyukov@google.com> wrote:

> > Are just utterly disgusting that turn perfectly readable code into an 
> > unreadable, unmaintainable mess.
> >
> > You need to find some better, cleaner solution please, or convince me that no 
> > such solution is possible. NAK for the time being.
> 
> Well, I can just write all functions as is. Does it better confirm to kernel 
> style?

I think writing the prototypes out as-is, properly organized, beats any of these 
macro based solutions.

> [...] I've just looked at the x86 atomic.h and it uses macros for similar 
> purpose (ATOMIC_OP/ATOMIC_FETCH_OP), so I thought that must be idiomatic kernel 
> style...

Mind fixing those too while at it?

And please squash any bug fixes and re-send a clean series against latest upstream 
or so.

Thanks,

	Ingo

[toc] | [prev] | [next] | [standalone]

#1608381 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Fri, Mar 24, 2017 at 11:57 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Dmitry Vyukov <dvyukov@google.com> wrote:
>
>> > Are just utterly disgusting that turn perfectly readable code into an
>> > unreadable, unmaintainable mess.
>> >
>> > You need to find some better, cleaner solution please, or convince me that no
>> > such solution is possible. NAK for the time being.
>>
>> Well, I can just write all functions as is. Does it better confirm to kernel
>> style?
>
> I think writing the prototypes out as-is, properly organized, beats any of these
> macro based solutions.

You mean write out the prototypes, but use what for definitions? Macros again?

>> [...] I've just looked at the x86 atomic.h and it uses macros for similar
>> purpose (ATOMIC_OP/ATOMIC_FETCH_OP), so I thought that must be idiomatic kernel
>> style...
>
> Mind fixing those too while at it?

I don't mind once I understand how exactly you want it to look.

> And please squash any bug fixes and re-send a clean series against latest upstream
> or so.
>
> Thanks,
>
>         Ingo

[toc] | [prev] | [next] | [standalone]

#1610383 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

* Dmitry Vyukov <dvyukov@google.com> wrote:

> On Fri, Mar 24, 2017 at 11:57 AM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > * Dmitry Vyukov <dvyukov@google.com> wrote:
> >
> >> > Are just utterly disgusting that turn perfectly readable code into an
> >> > unreadable, unmaintainable mess.
> >> >
> >> > You need to find some better, cleaner solution please, or convince me that no
> >> > such solution is possible. NAK for the time being.
> >>
> >> Well, I can just write all functions as is. Does it better confirm to kernel
> >> style?
> >
> > I think writing the prototypes out as-is, properly organized, beats any of these
> > macro based solutions.
> 
> You mean write out the prototypes, but use what for definitions? Macros again?

No, regular C code.

I don't see the point of generating all this code via CPP - it's certainly not 
making it more readable to me. I.e. this patch I commented on is a step backwards 
for readability.

I'd prefer repetition and a higher overall line count over complex CPP constructs.

Thanks,

	Ingo

[toc] | [prev] | [next] | [standalone]

#1610470 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Tue, Mar 28, 2017 at 09:52:32AM +0200, Ingo Molnar wrote:

> No, regular C code.
> 
> I don't see the point of generating all this code via CPP - it's certainly not 
> making it more readable to me. I.e. this patch I commented on is a step backwards 
> for readability.

Note that much of the atomic stuff we have today is all CPP already.

x86 is the exception because its 'weird', but most other archs are
almost pure CPP -- check Alpha for example, or asm-generic/atomic.h.

Also, look at linux/atomic.h, its a giant maze of CPP.

The CPP help us generate functions, reduces endless copy/paste (which
induces random differences -- read bugs) and construct variants
depending on the architecture input.

Yes, the CPP is a pain, but writing all that out explicitly is more of a
pain.



I've not yet looked too hard at these patches under consideration; and I
really wish we could get the compiler to do the right thing here, but
reducing the endless copy/paste that's otherwise the result of this, is
something I've found to be very valuable.

Not to mention that adding additional atomic ops got trivial (the set is
now near complete, so that's not much of an argument anymore -- but it
was, its what kept me sane sanitizing the atomic ops across all our 25+
architectures).

[toc] | [prev] | [next] | [standalone]

#1610493 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Tue, Mar 28, 2017 at 11:27 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, Mar 28, 2017 at 09:52:32AM +0200, Ingo Molnar wrote:
>
>> No, regular C code.
>>
>> I don't see the point of generating all this code via CPP - it's certainly not
>> making it more readable to me. I.e. this patch I commented on is a step backwards
>> for readability.
>
> Note that much of the atomic stuff we have today is all CPP already.
>
> x86 is the exception because its 'weird', but most other archs are
> almost pure CPP -- check Alpha for example, or asm-generic/atomic.h.
>
> Also, look at linux/atomic.h, its a giant maze of CPP.
>
> The CPP help us generate functions, reduces endless copy/paste (which
> induces random differences -- read bugs) and construct variants
> depending on the architecture input.
>
> Yes, the CPP is a pain, but writing all that out explicitly is more of a
> pain.
>
>
>
> I've not yet looked too hard at these patches under consideration; and I
> really wish we could get the compiler to do the right thing here, but
> reducing the endless copy/paste that's otherwise the result of this, is
> something I've found to be very valuable.
>
> Not to mention that adding additional atomic ops got trivial (the set is
> now near complete, so that's not much of an argument anymore -- but it
> was, its what kept me sane sanitizing the atomic ops across all our 25+
> architectures).


I am almost done with Ingo's proposal, including de-macro-ifying x86
atomic ops code.
I am ready to do either of them, I think both have pros and cons and
there is no perfect solution. But please agree on something.


While we are here, one thing that I noticed is that 32-bit atomic code
uses 'long long' for 64-bit operands, while 64-bit code uses 'long'
for 64-bit operands. This sorta worked more of less before, but
ultimately it makes it impossible to write any portable code (e.g. you
don't know what format specifier to use to print return value of
atomic64_read, nor what local variable type to use to avoid compiler
warnings). With the try_cmpxchg it become worse, because 'long*' is
not convertible to 'long long*' so it is not possible to write any
portable code that uses it. If you declare 'old' variable as 'long'
32-bit code won't compile, if you declare it as 'long long' 64-bit
code won't compiler. I think we need to switch to a single type for
64-bit operands/return values, e.g. 'long long'.

[toc] | [prev] | [next] | [standalone]

#1610507 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Tue, Mar 28, 2017 at 11:51 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Peter Zijlstra <peterz@infradead.org> wrote:
>
>> On Tue, Mar 28, 2017 at 09:52:32AM +0200, Ingo Molnar wrote:
>>
>> > No, regular C code.
>> >
>> > I don't see the point of generating all this code via CPP - it's certainly not
>> > making it more readable to me. I.e. this patch I commented on is a step backwards
>> > for readability.
>>
>> Note that much of the atomic stuff we have today is all CPP already.
>
> Yeah, but there it's implementational: we pick up arch primitives depending on
> whether they are defined, such as:
>
> #ifndef atomic_read_acquire
> # define atomic_read_acquire(v)         smp_load_acquire(&(v)->counter)
> #endif
>
>> x86 is the exception because its 'weird', but most other archs are
>> almost pure CPP -- check Alpha for example, or asm-generic/atomic.h.
>
> include/asm-generic/atomic.h looks pretty clean and readable overall.
>
>> Also, look at linux/atomic.h, its a giant maze of CPP.
>
> Nah, that's OK, much of is is essentially __weak inlines implemented via CPP -
> i.e. CPP is filling in a missing compiler feature.
>
> But this patch I replied to appears to add instrumentation wrappery via CPP which
> looks like excessive and avoidable obfuscation to me.
>
> If it's much more readable and much more compact than the C version then maybe,
> but I'd like to see the C version first and see ...
>
>> The CPP help us generate functions, reduces endless copy/paste (which induces
>> random differences -- read bugs) and construct variants depending on the
>> architecture input.
>>
>> Yes, the CPP is a pain, but writing all that out explicitly is more of a
>> pain.
>
> So I'm not convinced that it's true in this case.
>
> Could we see the C version and compare? I could be wrong about it all.

Here it is (without instrumentation):
https://gist.github.com/dvyukov/e33d580f701019e0cd99429054ff1f9a

Instrumentation will add for each function:

 static __always_inline void atomic64_set(atomic64_t *v, long long i)
 {
+       kasan_check_write(v, sizeof(*v));
        arch_atomic64_set(v, i);
 }

[toc] | [prev] | [next] | [standalone]

#1610528 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

* Dmitry Vyukov <dvyukov@google.com> wrote:

> > So I'm not convinced that it's true in this case.
> >
> > Could we see the C version and compare? I could be wrong about it all.
> 
> Here it is (without instrumentation):
> https://gist.github.com/dvyukov/e33d580f701019e0cd99429054ff1f9a

Could you please include the full patch so that it can be discussed via email and 
such?

> Instrumentation will add for each function:
> 
>  static __always_inline void atomic64_set(atomic64_t *v, long long i)
>  {
> +       kasan_check_write(v, sizeof(*v));
>         arch_atomic64_set(v, i);
>  }

That in itself looks sensible and readable.

Thanks,

	Ingo

[toc] | [prev] | [next] | [standalone]

#1611203 — Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

On Tue, Mar 28, 2017 at 12:15 PM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Dmitry Vyukov <dvyukov@google.com> wrote:
>
>> > So I'm not convinced that it's true in this case.
>> >
>> > Could we see the C version and compare? I could be wrong about it all.
>>
>> Here it is (without instrumentation):
>> https://gist.github.com/dvyukov/e33d580f701019e0cd99429054ff1f9a
>
> Could you please include the full patch so that it can be discussed via email and
> such?


Mailed the whole series.


>> Instrumentation will add for each function:
>>
>>  static __always_inline void atomic64_set(atomic64_t *v, long long i)
>>  {
>> +       kasan_check_write(v, sizeof(*v));
>>         arch_atomic64_set(v, i);
>>  }
>
> That in itself looks sensible and readable.
>
> Thanks,
>
>         Ingo

[toc] | [prev] | [next] | [standalone]

Page 1 of 2  [1] 2  Next page →

Back to top | Article view | linux.kernel

csiph-web