[Bug 192889] New: accept4 socket hangs in CLOSED (memcached)

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Thu Aug 21 14:40:08 UTC 2014


            Bug ID: 192889
           Summary: accept4 socket hangs in CLOSED (memcached)
           Product: Base System
           Version: 10.0-STABLE
          Hardware: amd64
                OS: Any
            Status: Needs Triage
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: arne.claus at trivago.com

We encountered that our memcached instances on FreeBSD 10 were rejecting
connections after being under heavy load. The machines showed several thousand
connections stuck in CLOSED (sometimes CLOSED_WAIT).

We could reproduce the issue several times using a load script.
There is a corresponding memcached bug with more information on the tests:

We assume that this issue is a FreeBSD 10 related because:
- The memcached source does not seem to do anything wrong (at first glance)
- The issue does not seem to happen when switching from accept4 to accept
(tests pending)
- According to our admins the connections were closed after enabling
- According to our admins this bug did not appear on FreeBSD 9 machines

We are still running tests to verify that this bug does only happen on FreeBSD
10 and is accept4 related. The current tests point in this direction.
accept4 uses the flag SOCK_NONBLOCK

Memcached version: 1.4.20
FreeBSD version:  10.0-STABLE #0 r269376

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