From: Vitaly Buka via Libc-alpha <libc-alpha@sourceware.org>
To: Paul Pluzhnikov <ppluzhnikov@google.com>
Cc: GLIBC Devel <libc-alpha@sourceware.org>
Subject: Re: [PATCH] stdlib: Fix data race in __run_exit_handlers
Date: Sun, 20 Sep 2020 16:36:32 -0700 [thread overview]
Message-ID: <CAPjTjwudpZ2bC-pCpqDddPVzH27u_1U1xeUXye1TmvAaskKxtw@mail.gmail.com> (raw)
In-Reply-To: <CAPjTjwvjLdBfU0ZQECaxn__FHdcLx7RK+z-3oBA1XZq8Q2GZcw@mail.gmail.com>
Oh, this atomics are not what I thought. So the test reproduced bugs in the
test.
I tried different approaches and I failed to reproduce the data race.
On Sun, 20 Sep 2020 at 14:26, Vitaly Buka <vitalybuka@google.com> wrote:
>
>
> On Sun, 20 Sep 2020 at 13:42, Paul Pluzhnikov <ppluzhnikov@google.com>
> wrote:
>
>> On Sun, Sep 20, 2020 at 5:10 AM Vitaly Buka via Libc-alpha
>> <libc-alpha@sourceware.org> wrote:
>>
>> > +static void *
>> > +threadfunc (void *unused)
>> > +{
>> > + for (; done < 1e6;)
>> > + {
>> > + if (added < done + 100)
>> > + {
>> > + __cxa_atexit (&atexitcb, (void *)(++added), __dso_handle);
>>
>> Isn't there a data race on "added" here (in addition to a data race on
>> "done")?
>> What prevents two threads from observing "added == 100" at the same
>> time and adding two calls with value of 101, which would later trigger
>> abort() in exitcb()?
>>
>
> They are atomic. Isn't (++added) guarantee to return different values in
> all threads?
>
>
>>
>> > + /* With default 8MiB Linux stack size, creating 1024 threads can
>> cause
>> > + VM exhausiton on 32-bit machines. Reduce stack size of each
>> thread to
>> > + 128KiB for a maximum required VM size of 128MiB. */
>>
>> This comment is far removed from the computation of kStacksize (and
>> the name violates the naming conventions used here).
>>
>> I suggest:
>>
>> size_t stack_size = 128 << 10; /* 128KiB */
>> if (stack_size < PTHREAD_STACK_MIN) stack_size = PTHREAD_STACK_MIN;
>>
>> Also, I suspect that 32KiB would be more than enough for stack size here.
>>
>> > + for (i = 0; i < kNumThreads; ++i)
>>
>> Since kNumThreads isn't used anywhere else, I suggest making it a local:
>>
>> const int num_threads = 50;
>>
>> --
>> Paul Pluzhnikov
>>
>
next prev parent reply other threads:[~2020-09-20 23:37 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-20 9:57 [PATCH] stdlib: Fix data race in __run_exit_handlers Vitaly Buka via Libc-alpha
2020-09-20 12:09 ` Vitaly Buka via Libc-alpha
2020-09-20 20:41 ` Paul Pluzhnikov via Libc-alpha
2020-09-20 21:26 ` Vitaly Buka via Libc-alpha
2020-09-20 23:36 ` Vitaly Buka via Libc-alpha [this message]
2020-09-20 23:37 ` Vitaly Buka via Libc-alpha
2020-09-21 8:31 ` Vitaly Buka via Libc-alpha
2020-09-30 16:01 ` Joseph Myers
2021-04-17 16:16 ` Vitaly Buka via Libc-alpha
2021-04-17 17:11 ` Vitaly Buka via Libc-alpha
2021-04-17 17:13 ` Vitaly Buka via Libc-alpha
2021-04-17 17:22 ` Vitaly Buka via Libc-alpha
2021-04-17 18:01 ` Paul Pluzhnikov via Libc-alpha
2021-04-20 22:51 ` Vitaly Buka via Libc-alpha
2021-04-20 23:40 ` Paul Pluzhnikov via Libc-alpha
2021-04-26 19:20 ` Vitaly Buka via Libc-alpha
2021-04-26 19:23 ` Vitaly Buka via Libc-alpha
2021-04-26 19:27 ` Vitaly Buka via Libc-alpha
2021-05-13 13:15 ` Adhemerval Zanella via Libc-alpha
2021-05-14 6:50 ` Vitaly Buka via Libc-alpha
2021-04-17 17:36 ` Paul Pluzhnikov via Libc-alpha
2021-04-17 20:19 ` Florian Weimer
2021-04-19 2:48 ` Vitaly Buka via Libc-alpha
2021-04-19 2:57 ` Vitaly Buka via Libc-alpha
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