malloc crash

Mark Geisert
Tue Oct 26 00:54:07 GMT 2021

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:
>>>>> On Oct 25 08:35, Ken Brown wrote:
>>>>>> On 10/25/2021 4:59 AM, Corinna Vinschen wrote:
>>>>>>> Has the thread already been started at this point?
>>>>>> Yes, here's the backtrace of that thread:
>>>>>> Thread 5 (Thread 9692.0x7c4c):
>>>>>> #0  0x00000001801934f9 in sys_alloc (m=0x18036f860 <_gm_>, nb=1040) at
>>>>>> ../../../../temp/winsup/cygwin/
>>>>>> #1  0x0000000180196b96 in dlmalloc (bytes=1024) at
>>>>>> ../../../../temp/winsup/cygwin/
>>>>>> #2  0x00000001801993e1 in dlrealloc (oldmem=0x0, bytes=1024) at
>>>>>> ../../../../temp/winsup/cygwin/
>>>>>> #3  0x00000001800e8eed in realloc (p=0x0, size=1024) at
>>>>>> ../../../../temp/winsup/cygwin/
>>>>> 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
>> 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.


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