Re: pg15b1: FailedAssertion("val > base", File: "...src/include/utils/relptr.h", Line: 67, PID: 30485)

Justin Pryzby <pryzby@telsasoft.com> writes:
> ./tmp_install/usr/local/pgsql/bin/postgres -D ./src/test/regress/tmp_check/data -c min_dynamic_shared_memory=1MB
> TRAP: FailedAssertion("val > base", File: "../../../../src/include/utils/relptr.h", Line: 67, PID: 21912)

Yeah, I see it too.

> It looks like this may be pre-existing problem exposed by
> commit e07d4ddc55fdcf82082950b3eb0cd8f728284c9d

Agreed.  Here I see

#5  FreePageManagerInitialize (fpm=fpm@entry=0x7f34b3ddd300, 
    base=base@entry=0x7f34b3ddd300 "") at freepage.c:187
#6  0x000000000082423e in dsm_shmem_init () at dsm.c:473

so that where we do

	relptr_store(base, fpm->self, fpm);

the "relative" pointer value would have to be zero, making the case
indistinguishable from a NULL pointer.  We can either change the
caller so that these addresses aren't the same, or give up the
ability to store NULL in relptrs ... doesn't seem like a hard call.

One interesting question I didn't look into is why it takes a nondefault
value of min_dynamic_shared_memory to expose this bug.

			regards, tom lane