Re: <jemalloc>: jemalloc_arena.c:182: Failed assertion: "p[i] == 0"

On Apr 21, 2012, at 11:54 AM, David Wolfskill wrote:
> After applying Dimitry Andric's patches to contrib/jemalloc and replacing
> /usr/bin/as with one built last Sunday, I was finally(!) able to rebuild
> head as of 234536:
> 
> FreeBSD freebeast.catwhisker.org 10.0-CURRENT FreeBSD 10.0-CURRENT #797 234536M: Sat Apr 21 10:23:33 PDT 2012     root_at_freebeast.catwhisker.org:/usr/obj/usr/src/sys/GENERIC  i386
> 
> However, as I was copying a /usr/obj hierarchy via tar -- e.g.:
> 
> root_at_freebeast:/common/home/david # (cd /var/tmp && rm -fr obj && mkdir obj) && (cd /usr && tar cpf - obj) | (cd /var/tmp && tar xpf -)
> 
> it ran for a while, then:
> 
> <jemalloc>: jemalloc_arena.c:182: Failed assertion: "p[i] == 0"
> Abort (core dumped) 
> root_at_freebeast:/common/home/david # echo $?
> 134
> root_at_freebeast:/common/home/david # ls -lTio *.core
> ls: No match.
> root_at_freebeast:/common/home/david # 
> 
> So ... no core file, apparently.
> 
> freebeast(10.0-C)[2] find /usr/src/contrib/jemalloc -type f -name jemalloc_arena.c
> freebeast(10.0-C)[3] 
> 
> No file named "jemalloc_arena.c", either.
> 
> But contrib/jemalloc/src/arena.c contains a function,
> arena_chunk_validate_zeroed():
> 
>    175 static inline void
>    176 arena_chunk_validate_zeroed(arena_chunk_t *chunk, size_t run_ind)
>    177 {
>    178         size_t i;
>    179         UNUSED size_t *p = (size_t *)((uintptr_t)chunk + (run_ind << LG_PAGE));
>    180
>    181         for (i = 0; i < PAGE / sizeof(size_t); i++)
>    182                 assert(p[i] == 0);
>    183 }
> 
> Thoughts?

I received a similar report yesterday in the context of filezilla, but didn't get as far as reproducing it.  I think the problem is in chunk_alloc_dss(), which dangerously claims that newly allocated memory is zeroed.  It looks like I formalized this bad assumption in early 2010, though the bug existed before that.  It's a bigger deal now because sbrk() is preferred over mmap(), so the bug has languished for a couple of years.  I'll get a fix committed today (and revert the order of preference between sbrk() and mmap()).

By the way, I wonder why not everyone hits this (I don't).

Thanks,
Jason