user/dev discussion of public-inbox itself
 help / color / Atom feed
* [PATCH] examples/*@.service: sockets MUST be NonBlocking
@ 2019-06-30  7:41 Eric Wong
  0 siblings, 0 replies; only message in thread
From: Eric Wong @ 2019-06-30  7:41 UTC (permalink / raw)
  To: meta

For users running multiple (-nntpd@1, -nntpd@2) instances of
either -httpd or -nntpd via systemd to implement zero-downtime
restarts; it's possible for a listen socket to become blocking
for a moment during an accept syscall and cause a daemons to
get stuck in a blocking accept() during
PublicInbox::Listener::event_step (event_read in previous
versions).

Since O_NONBLOCK is a file description flag, systemd clearing
O_NONBLOCK momentarily (before PublicInbox::Listener::new
re-enables it) creates a window for another instance of our
daemon to get stuck in accept().

cf. systemd.service(5)
---
  Additional warnings and tests for this race coming;
  but I need food + sleep.

  I kinda wished I'd pushed for accept4(..., SOCK_DONTWAIT):
  https://lore.kernel.org/lkml/20150513023712.GA4206@dcvr.yhbt.net/

 examples/public-inbox-httpd@.service | 5 +++++
 examples/public-inbox-nntpd@.service | 5 +++++
 examples/unsubscribe-psgi@.service   | 5 +++++
 3 files changed, 15 insertions(+)

diff --git a/examples/public-inbox-httpd@.service b/examples/public-inbox-httpd@.service
index 56117ef..e811da4 100644
--- a/examples/public-inbox-httpd@.service
+++ b/examples/public-inbox-httpd@.service
@@ -20,7 +20,12 @@ ExecStartPre = /bin/mkdir -p -m 1777 /tmp/.pub-inline
 ExecStart = /usr/local/bin/public-inbox-httpd \
 -1 /var/log/public-inbox/httpd.out.log
 StandardError = syslog
+
+# NonBlocking is REQUIRED to avoid a race condition if running
+# simultaneous services
+NonBlocking = true
 Sockets = public-inbox-httpd.socket
+
 KillSignal = SIGQUIT
 User = nobody
 Group = nogroup
diff --git a/examples/public-inbox-nntpd@.service b/examples/public-inbox-nntpd@.service
index 62202c2..a879841 100644
--- a/examples/public-inbox-nntpd@.service
+++ b/examples/public-inbox-nntpd@.service
@@ -20,7 +20,12 @@ ExecStartPre = /bin/mkdir -p -m 1777 /tmp/.pub-inline
 ExecStart = /usr/local/bin/public-inbox-nntpd \
 -1 /var/log/public-inbox/nntpd.out.log
 StandardError = syslog
+
+# NonBlocking is REQUIRED to avoid a race condition if running
+# simultaneous services
+NonBlocking = true
 Sockets = public-inbox-nntpd.socket
+
 KillSignal = SIGQUIT
 User = nobody
 Group = nogroup
diff --git a/examples/unsubscribe-psgi@.service b/examples/unsubscribe-psgi@.service
index acc29e8..c8721fb 100644
--- a/examples/unsubscribe-psgi@.service
+++ b/examples/unsubscribe-psgi@.service
@@ -12,7 +12,12 @@ After = unsubscribe-psgi.socket
 # any PSGI server ought to work,
 # but public-inbox-httpd supports socket activation like unsubscribe.milter
 ExecStart = /usr/local/bin/public-inbox-httpd -W0 /etc/unsubscribe.psgi
+
+# NonBlocking is REQUIRED to avoid a race condition if running
+# simultaneous services
+NonBlocking = true
 Sockets = unsubscribe-psgi.socket
+
 # we need to modify the mlmmj spool
 User = mlmmj
 KillMode = process
-- 
EW


^ permalink raw reply	[flat|nested] only message in thread

only message in thread, back to index

Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-06-30  7:41 [PATCH] examples/*@.service: sockets MUST be NonBlocking Eric Wong

user/dev discussion of public-inbox itself

Archives are clonable:
	git clone --mirror http://public-inbox.org/meta
	git clone --mirror http://czquwvybam4bgbro.onion/meta
	git clone --mirror http://hjrcffqmbrq6wope.onion/meta
	git clone --mirror http://ou63pmih66umazou.onion/meta

Newsgroups are available over NNTP:
	nntp://news.public-inbox.org/inbox.comp.mail.public-inbox.meta
	nntp://ou63pmih66umazou.onion/inbox.comp.mail.public-inbox.meta
	nntp://czquwvybam4bgbro.onion/inbox.comp.mail.public-inbox.meta
	nntp://hjrcffqmbrq6wope.onion/inbox.comp.mail.public-inbox.meta
	nntp://news.gmane.org/gmane.mail.public-inbox.general

 note: .onion URLs require Tor: https://www.torproject.org/

AGPL code for this site: git clone https://public-inbox.org/ public-inbox