[Bug libc/11787] Program with large TLS segment fails aio_write

["ppluzhnikov at google dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=11787

--- Comment #12 from Paul Pluzhnikov <ppluzhnikov at google dot com> 2012-03-24 02:21:06 UTC ---
(In reply to comment #8)

> Please note that the aio helper thread *should* be using a default 2MB stack on
> x86, not 16K, I don't see anywhere that sets the helper threads stack to 16K.

The helper thread stack size *is* set by __pthread_get_minstack.

The test case here no longer crashes using the current git trunk, but only
because the aio thread stack is now increased to accomodate static tls:

  // nptl/nptl-init.c
  size_t
  __pthread_get_minstack (const pthread_attr_t *attr)
  {
    struct pthread_attr *iattr = (struct pthread_attr *) attr;

    return (GLRO(dl_pagesize) + __static_tls_size + PTHREAD_STACK_MIN
        + iattr->guardsize);
  }

This was done here:

2011-12-22  Ulrich Drepper  <drepper@gmail.com>

       [BZ #13088]
       * sysdeps/unix/sysv/linux/timer_routines.c: Get minimum stack size
       through __pthread_get_minstack.
       * nptl-init.c (__pthread_initialize_minimal_internal): Get page size
       directly from _rtld_global_ro.
       (__pthread_get_minstack): New function.
       * pthreadP.h: Declare __pthread_get_minstack.
       * Versions (libpthread) [GLIBC_PRIVATE]: Add __pthread_get_minstack.

and is *precisely* the change we are asking for for the other threads.

I see that Rich Felker is in exact agreement with me:
http://sourceware.org/bugzilla/show_bug.cgi?id=13088#c1

> You are also increasing the memory footprint of all applications that use TLS
> that worked fine before.

It depends on what you call "memory footprint". Yes, we'll increase memory
we *reserve* for stacks (VM size). But we will not *use* any more memory
than what's already used (RSS).

I think the only application that would notice this is one that was almost
running out of VM space. An answer for such app would be to decrease its
default stack sizes, use smaller number of threads, or switch to 64 bits.

> Before making any changes we need to hear from the distros (RH, SuSE, Debian,
> Gentoo, Ubuntu etc) about the kind of impact this might have e.g. a quick find
> / readelf -a / grep to determine on average the memory increase we are looking
> at.

Would above still apply if it's just VM size we are talking about?
I don't see how readelf will reveal anything.

> There are multiple cases here.

> You appear to be suggesting the following:
> 
> For (a) the behaviour remains the same.
> 
> For (b) we adjust upward by the size of the static TLS data.
> 
> For (c) "
> 
> For (d) "
> 
> For (e) "

Yes, I believe that's what we are proposing.

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