On 2014-05-06 13:33:01 +0300, Heikki Linnakangas wrote: > On 03/31/2014 09:08 PM, Robert Haas wrote: > >On Wed, Mar 26, 2014 at 9:45 PM, Peter Geoghegan <p...@heroku.com> wrote: > >>On Wed, Nov 27, 2013 at 9:10 AM, Noah Misch <n...@leadboat.com> wrote: > >>>The threat is that rounding the read size up to the next MAXALIGN would > >>>cross > >>>into an unreadable memory page, resulting in a SIGSEGV. Every palloc chunk > >>>has MAXALIGN'd size under the hood, so the excess read of "toDelete" cannot > >>>cause a SIGSEGV. For a stack variable, it depends on the ABI. I'm not > >>>aware > >>>of an ABI where the four bytes past the end of this stack variable could be > >>>unreadable, which is not to claim I'm well-read on the topic. We should > >>>fix > >>>this in due course on code hygiene grounds, but I would not back-patch it. > >> > >>Attached patch silences the "Invalid read of size n" complaints of > >>Valgrind. I agree with your general thoughts around backpatching. Note > >>that the patch addresses a distinct complaint from Kevin's, as > >>Valgrind doesn't take issue with the invalid reads past the end of > >>spgxlogPickSplit variables on the stack. > > > >Is the needless zeroing this patch introduces apt to cause a > >performance problem? > > > >This function is actually pretty wacky. If we're stuffing bytes with > >undefined contents into the WAL record, maybe the answer isn't to > >force the contents of those bytes to be defined, but rather to elide > >them from the WAL record. > > Agreed. I propose the attached, which removes the MAXALIGNs. It's not > suitable for backpatching, though, as it changes the format of the WAL > record.
Not knowing anything about spgist this looks sane to me. Do we need a backpatchable solution given that we seem to agree that these bugs aren't likely to cause harm? Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
