From: Mark Geisert <mark@maxrnd.com>
To: cygwin-developers@cygwin.com
Subject: Re: malloc crash
Date: Tue, 26 Oct 2021 01:59:36 -0700 [thread overview]
Message-ID: <b8ea3fc0-0cb5-fa84-a087-112d6b6631ae@maxrnd.com> (raw)
In-Reply-To: <20211026175229.1eda36caab1b03314a8cf165@nifty.ne.jp>
Takashi Yano wrote:
> On Tue, 26 Oct 2021 01:30:13 -0700
> Mark Geisert wrote:
>> Replying to myself to correct something I wrote...
>>
>> Mark Geisert wrote:
>>> Takashi Yano wrote:
>>>> On Mon, 25 Oct 2021 16:36:50 -0700
>>>> Mark Geisert wrote:
>>>>> Ken Brown wrote:
>>>>>> On 10/25/2021 5:29 PM, Mark Geisert wrote:
>>>>>>> Corinna Vinschen wrote:
>>>>>>>> Er... huh? So both threads are in a malloc function? This shouldn't
>>>>>>>> have happened, given the clunky muto guarding malloc calls. This is
>>>>>>>> really strange. Why's the muto not working here?
>>>>>>>
>>>>>>> Is it possible both threads have executed malloc_init()?
>>>>>>> If so, the second one would reinit the muto.
>>>>>>
>>>>>> Or does the fifo_reader thread call a malloc function before the main thread has
>>>>>> called malloc_init()? This would presumably cause __malloc_lock() to fail, but
>>>>>> there's no error check.
>>>>>
>>>>> If there's a global constructor involved, that is known to happen. Constructors
>>>>> are run from dll_crt0_0(), before malloc_init() is called from dll_crt0_1(). See
>>>>> dcrt0.cc for the details.
>>>>
>>>> So how about moving malloc_init() call from dll_crt0_1() to dll_crl0_0()
>>>> so that malloc() can be called in fixup_after_fork/exec()?
>>>
>>> It appears simple, but this is a touchy area of code. The _0 and _1 are two
>>> separate phases of process startup. I'd want to hear Corinna's thoughts on this.
>>>
>>> I'd also like to verify somehow that this is the scenario Ken is hitting.
>>>
>>> When I was researching different mallocs for Cygwin I hit the constructor snag
>>> repeatedly. I did try delaying the constructor-running until after malloc_init().
>>> More problems. I did not try moving malloc_init() to before the constructor run.
>>
>> Apologies; this was many months ago. What I did try was moving the malloc_init()
>> to before running the constructor chain, as Takashi suggested. That is what gave
>> me more problems. I don't recall what they were, but I reverted that attempt.
>>
>> The "future malloc" build of Cygwin I'm running doesn't exhibit Ken's issue, as
>> far as I can tell. It has a specific fix to avoid the scenario I've been talking
>> about here, but I don't want to take us down that path unless we're sure Ken's
>> hitting that same scenario.
>
> I tried the following patch, and confirmed that the issue has
> been disappeared. I do not notice any other problems so far
> with this patch.
>
> diff --git a/winsup/cygwin/dcrt0.cc b/winsup/cygwin/dcrt0.cc
> index 6f4723bb0..0d541ec14 100644
> --- a/winsup/cygwin/dcrt0.cc
> +++ b/winsup/cygwin/dcrt0.cc
> @@ -773,6 +773,10 @@ dll_crt0_0 ()
> do_global_ctors (&__CTOR_LIST__, 1);
^^^^^^^^^^^^^^^
> cygthread::init ();
>
> + /* malloc_init() has been moved from dll_crt0_1() to here so that
> + malloc() can be called in fixup_after_exec(). */
> + malloc_init ();
> +
> if (!child_proc_info)
> {
> setup_cygheap ();
> @@ -857,7 +861,7 @@ dll_crt0_1 (void *)
> on a functioning malloc and it's possible that the user's program may
> have overridden malloc. We only know about that at this stage,
> unfortunately. */
> - malloc_init ();
> + /* malloc_init() has been moved to dll_crt0_0(). */
> user_shared->initialize ();
>
> #ifdef CYGHEAP_DEBUG
>
>
> Where is the "constructor chain" you mentioned?
See above. Try moving your new lines above the call to do_global_ctors(). Also
note the comment just above the original location of those lines.. you're now
ignoring what the comment warns about.
..mark
next prev parent reply other threads:[~2021-10-26 8:59 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-24 21:46 Ken Brown
2021-10-25 8:56 ` Takashi Yano
2021-10-25 13:37 ` Ken Brown
2021-10-25 8:59 ` Corinna Vinschen
2021-10-25 12:35 ` Ken Brown
2021-10-25 15:39 ` Corinna Vinschen
2021-10-25 21:29 ` Mark Geisert
2021-10-25 22:02 ` Ken Brown
2021-10-25 23:36 ` Mark Geisert
2021-10-26 0:18 ` Takashi Yano
2021-10-26 0:54 ` Mark Geisert
2021-10-26 8:30 ` Mark Geisert
2021-10-26 8:52 ` Takashi Yano
2021-10-26 8:59 ` Mark Geisert [this message]
2021-10-26 9:26 ` Takashi Yano
2021-10-26 9:31 ` Corinna Vinschen
2021-10-26 9:28 ` Corinna Vinschen
2021-10-26 9:27 ` Corinna Vinschen
2021-10-26 9:24 ` Corinna Vinschen
2021-10-26 14:32 ` Ken Brown
2021-10-26 16:03 ` Corinna Vinschen
2021-10-26 16:36 ` Ken Brown
2021-10-26 16:49 ` Corinna Vinschen
2021-10-26 17:10 ` Ken Brown
2021-10-27 0:44 ` Takashi Yano
2021-10-27 9:01 ` Corinna Vinschen
2021-10-26 16:44 ` Takashi Yano
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