Re: [PATCH] malloc: Perform full initialization before __malloc_check_init

[Florian Weimer <fweimer at redhat dot com>]

On 09/21/2017 08:15 PM, Wilco Dijkstra wrote:
> Florian Weimer wrote:
>
> Well it looks like the malloc initialization is insane. It sets default hooks for
> malloc/realloc/etc which call ptmalloc_init, which is completely unguarded
> from multi-threaded execution...

I have tried to explain repeatedly why this is not a problem: 
pthread_create calls malloc before launching a new thread, so 
ptmalloc_init is always run in single-thread mode.

> Then it implicitly relies on have_fastchunks
> being true (from zero-initialization of main_arena by inverting the meaning of
> the flag), which should eventually result in a call to malloc_consolidate, which
> assuming max_fast hasn't yet been set, finally calls malloc_init_state...

Sure, it's convoluted.

> +    {
> +      /* Perform full initialization.  */
> +      malloc_consolidate (&main_arena);
> +      __malloc_check_init ();
> +    }
>
> That's an improvement but ptmalloc_init should call malloc_init_state (&main_arena)
> in all cases. The check in malloc_consolidate should then be removed (no idea why
> anyone would want to delay initialization to that point...). Interestingly malloc_init_state
> is called for other arenas...

I didn't want to touch until we remove the hooks and have to overhaul 
the initialization procedure anyway (i.e., detect whether malloc has 
been interposed, and if not, perform malloc initialization during 
process startup before calling ELF constructors and main).

Thanks,
Florian