Re: [PATCH 0/2] fix http deadlock on giant ref negotiations

On Fri, May 15, 2015 at 10:44:50AM +0200, Dennis Kaarsemaker wrote:

quoted

I applied the test from your patch, but couldn't get it to fail even
with stock git.  The test above it shrunk a bit, but I was able to tweak
yours to generate tags from 2001..100000, which I thought would have
worked.  I suspect it's something silly like the size not being quite
big enough for the pipe buffer on my system, or something like that.
Though I couldn't get it to fail even with 200,000 tags, so perhaps it's
something else.

The shrinkage in the test above it will actually work around the issue,
as there are now fewer already-fetched tags to negotiate. Either
reverting that shrinkage or executing the new test twice should do the
trick.

Ah, right, that makes sense. I was creating the right number of tags,
but not with half of them already in the repo when I did the critical
fetch. I got it to fail by adding and fetching another 48,000, and then
adding and fetching another 50,000 on top of that.

Interestingly, with my patch the _first_ fetch fails, that otherwise
succeeds with stock git. My patch sets a maximum size on the spool
buffer, and we exceed it. I guess 1MB isn't enough for pathological
cases. I'm hesitant to let it expand indefinitely for security reasons,
but we could probably bump it to 10MB or something.

I dunno. I'm not excited about introducing new size restrictions that
were not there before.

Maybe it's time to implement git-over-websockets. ;)

-Peff