Re: Curious buildfarm failures (fwd) - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Curious buildfarm failures (fwd)
Date
Msg-id 5103.1358290600@sss.pgh.pa.us
Whole thread Raw
In response to Re: Curious buildfarm failures (fwd)  (Andres Freund <andres@2ndquadrant.com>)
Responses Re: Curious buildfarm failures (fwd)
List pgsql-hackers
Andres Freund <andres@2ndquadrant.com> writes:
> I played a bit arround (thanks Sergey!) and it seems to be some rather
> strange optimization issue around the fsync request queue.

> Namely changing 
>     request->rnode = rnode;
> into
>     request->rnode.spcNode = rnode.spcNode;
>     request->rnode.dbNode = rnode.dbNode;
>     request->rnode.relNode = rnode.relNode;
> makes it pass reliably.

Jeez.  That's my candidate for weird compiler bug of the month.

> How the hell thats correlating with the elog changes I don't yet know.

There is an elog(ERROR) further up in the same function, but it's sure
not clear how that could cause the compiler to misimplement a struct
assignment.  Maybe the problem is not in those lines alone, but the fact
that rnode is a pass-by-value struct?  (That is, maybe it's the value of
the rnode local variable that's getting munged, somewhere up near the
elog call?)  We tend to not use pass-by-value struct params much, so we
might not have noticed a compiler bug associated with that.  Or IOW,
does changing ForwardFsyncRequest to use a "const RelFileNode *rnode"
parameter make it go away?
        regards, tom lane



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