Re: replication cleanup code incorrect way to use of HTAB HASH_REMOVE ?

On Sun, Mar 21, 2021 at 8:54 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Sat, Mar 20, 2021 at 12:54 PM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> >
> > PSA my patch to correct this by firstly doing a HASH_FIND, then only
> > HASH_REMOVE after we've finished using the ent.
> >
>
> Why can't we keep using HASH_REMOVE as it is but get the output (entry
> found or not) in the last parameter of hash_search API and then
> perform Assert based on that? See similar usage in reorderbuffer.c and
> rewriteheap.c.
>

Changing the Assert doesn't do anything to fix the problem as
described, i.e. dereferencing of ent after the HASH_REMOVE.

The real problem isn't the Assert. It's all those other usages of ent
disobeying the API rule: "(NB: in the case of the REMOVE action, the
result is a dangling pointer that shouldn't be dereferenced!)"

e.g.
- SharedFileSetDeleteAll(ent->stream_fileset);
- pfree(ent->stream_fileset);
- ent->stream_fileset = NULL;
- if (ent->subxact_fileset)
- SharedFileSetDeleteAll(ent->subxact_fileset);
- pfree(ent->subxact_fileset);
- ent->subxact_fileset = NULL;

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Kind Regards,
Peter Smith
Fujitsu Australia.