Many core dumps in pthread_getspecific.

[Konstantin Belousov]

On Sat, Jun 06, 2015 at 09:50:22AM +0200, Andre Meiser wrote:
> On Wed, Jun 03, 2015 at 16:58 +0200, Konstantin Belousov wrote:
> > You should recompile both libc and libthr with debugging symbols, like
> > cd /usr/src
> > (cd lib/libc && make all install DEBUG_FLAGS=-g)
> > (cd lib/libthr && make all install DEBUG_FLAGS=-g)
> > then obtain the core dump and post backtraces.
> 
> Thank you, that was exactly what I was looking for. Now I like FreeBSD
> even more. ;)
>
> I made this short after and also rebooted the entire system to make
> all programmes use those debug libs. Since than I had not a single
> core dump.
Which means, most likely, that your installation was corrupted.

>
> I experienced something similar in the past, that with activated
> debugging some errors can't be triggered any longer.
>
> At the moment I'm happy without crashes and I can work with this
> system. As soon as I'm getting a new core dump, I'll post the
> backtrace. If this won't happen for weeks, I may recompile the libs
> again, try to find a way to trigger the bug on purpose, enable the
> debug flag again and than provide the info.
>
> In the meantime, maybe a core developer may think about the lines
> of code I'd provided. Why is _get_curthread() compared to NULL at
> thr_kern.c (line 601) but not at thr_spec.c (line 224)? Either
> _get_curthread() never ever returns NULL, than it's pointless to test
> it or it's missing [not only] at thr_spec.c.
Whole thr_kern.c file is 213 lines long in the HEAD.
Might be, a core developer has a 601-lines long thr_kern.c.

The only way for _get_curthread() to return NULL or, more likely, a
garbage, is for the call to _get_curthread() to happens before the
threading machinery was initialized. WRT the thr_spec.c, correct code
must call pthread_key_create(3) at least once before calling any other
pthread_key_*(3) functions. The implementation of pthread_key_create(3)
interface, the function _pthread_key_create(), calls _thr_check_init()
as the first action, and this helper initializes threading. So if
_get_curthread() in any pthread_key_*() function returns NULL or
garbage, this is an application' bug.

>
> I'm using activated hyperthreading:
>
> % sysctl hw.model hw.machine hw.ncpu hw.model: Intel(R) Xeon(R) CPU
> E5-1620 v2 @ 3.70GHz hw.machine: amd64 hw.ncpu: 8
>
> Sincerely yours Andre. _______________________________________________
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