First of all, thanks for helping me in this!

> Am 14.01.2019 um 21:32 schrieb William A Rowe Jr <wr...@rowe-clan.net>:
> 
> On Mon, Jan 14, 2019 at 12:56 PM Stefan Sperling <s...@stsp.name> wrote:
> On Mon, Jan 14, 2019 at 11:38:55AM -0600, William A Rowe Jr wrote:
> > On Mon, Jan 14, 2019 at 8:42 AM Stefan Sperling <s...@stsp.name> wrote:
> > >
> > > FYI, the reason APR pool debugging is enabled in production on OpenBSD
> > > is because, after Heartbleed, OpenBSD decided to force 3rd party software
> > > to use the operating system's malloc/free implementation instead of custom
> > > allocators, where possible.
> > >
> > > If there was another way to make APR pools map directly to malloc/free
> > > I would like to know about it. As far as I undestand, APR pools will
> > > cache freed memory unless pool debugging is enabled.
> > 
> > Your assessment is correct and by design. The argument by OpenBSD
> > makes as much sense as attempting to force C construction/destruction
> > on C++ sources, and OpenBSD users should expect side-effects of this
> > rather radical change. APR pool Debugging has never been tested for
> > the same level of robustness as the 'release' pool mechanics, nor have
> > the many applications which are built upon APR pools. OpenBSD needs
> > to consider their "port" of these many APR-consuming applications as
> > independently maintained.
> 
> >Well, I am quite happy with it as it is forcing me to fix bugs such as this
> >one which nobody cared to fix for a decade (the quoted comment was written
> >by gstein before SVN 1.0): https://svn.apache.org/r1850651
> 
> Yes, there are absolutely benefits to testing code under the AP_POOL_DEBUG
> logic. My comments speak to the amount of testing and scrutiny that the
> pool debug logic itself has been subjected to.

I understand the benefits, but the production use really bites me. It means
that I need to double my test builds and runs. That cuts into time I'd rather
invest in other things.

Stefan: which DEBUG flags are "you" using in production for OpenBSD? I
would like to run some h2 tests in exactly that setting...

> It seems that the mode was overloaded with too many meanings. If I had
> to break them all out, they might look like;
> 
> Typical allocator / subpool default behavior
> Implicit allocator per subpool
> 
> Typical allocator default reuse behavior
> Free on pool release
> Lock no-read/no-write on pool release (debugging: no address reuse)
> 
> And re-implement the previously broken apr_pool_lock() for read-only
> access to write-once/nonvolatile-on-fork pools such as config data.
> 
> Then expand the API to permit some sort of apr_pool_split (_fork?)
> as a complement to apr_pool_join. Expand the API to indicate the
> handoff of the allocator from one thread to another or indicate that
> the pool is free-threaded.

Since APR will need to remain "stable" for existing applications, we
seem to talk bout API extensions that allow apps like mod_http2 to
specify their pool flavour more clearly. And that will then influence
the debug code assertions and tests.

But some current debug behaviour might need fixing before that, as I
see the case with the current thread assertions. That seems to be
over-optimized for a specific (but common) use case.

> The apr_allocator_max_free_set() value of 0 was wrong. Zero should
> always force no-reuse. -1 or similar should have been used for some
> unlimited allocation reuse. A value of 1 today effectively does the same
> thing as the correct implementation of 0.

Would OpenBSD be happy with a setting (COMPILE FLAG) that forces
the immediate free() by allocators and otherwise skipping the DEBUG
flags?

Personally, I would like that to be the default behaviour in httpd. The
current implementation seems to hinder use of modern address sanitation
tools and fuzzing. Something which has proven very valuable in h2.

> Just some thoughts to start off discussion.

Cheers, Stefan

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