Re: libthr and main thread stack size

On Mon, Sep 15, 2014 at 03:47:41PM -0600, Justin T. Gibbs wrote:
> On Aug 8, 2014, at 5:22 AM, Konstantin Belousov <kostikbel_at_gmail.com> wrote:
> 
> ?
> 
> > Below is the patch which adds environment variable
> > LIBPTHREAD_BIGSTACK_MAIN. Setting it to any value results in the
> > main thread stack left as is, and other threads allocate stack
> > below the area of RLIMIT_STACK. Try it. I do not want to set this
> > behaviour as default.
>
> Is there a reason this should not be the default? Looking at the
> getrlimit() page on the OpenGroup?s site they say:
>
> RLIMIT_STACK This is the maximum size of the initial thread's stack,
> in bytes. The implementation does not automatically grow the stack
> beyond this limit. If this limit is exceeded, SIGSEGV shall be
> generated for the thread. If the thread is blocking SIGSEGV, or the
> process is ignoring or catching SIGSEGV and has not made arrangements
> to use an alternate stack, the disposition of SIGSEGV shall be set to
> SIG_DFL before it is generated.
>
> Does posix say something different?
>
> I ran into this issue when debugging a segfault on Postgres when
> running an (arguably quite bogus) query that should have fit within
> both the configured stack rlimit and Postgres? configured stack limit.
> The Postgres backend is really just single threaded, but happens
> to pull in libpthread due to the threading support in some of the
> libraries it uses. The segfault definitely violates POLA.
>
> ? Justin

I am conservative to not disturb the address space layout in single go.
If enough people test this setting, I can consider flipping the default
to the reverse.

I am still curious why the things were done in this way, but nobody
replied.