From d7eac3e0ae20510e2737dc4e23975391fef5ece3 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Michal=20Koutn=C3=BD?= <mkoutny@suse.com>

Date: Tue, 16 Jan 2018 19:22:46 +0100

Subject: [PATCH] core/timer: Prevent timer looping when unit cannot start

When a unit job finishes early (e.g. when fork(2) fails) triggered unit goes

through states

        stopped->failed (or failed->failed),

in case a ExecStart= command fails unit passes through

        stopped->starting->failed.

The former transition doesn't result in unit active/inactive timestamp being

updated and timer (OnUnitActiveSec= or OnUnitInactiveSec=) would use an expired

timestamp triggering immediately again (repeatedly).

This patch exploits timer's last trigger timestamp to ensure the timer isn't

triggered more frequently than OnUnitActiveSec=/OnUnitInactiveSec= period.

Steps to reproduce:

0) Create sample units:

cat >~/.config/systemd/user/looper.service <

[Service]

ExecStart=/usr/bin/sleep 2

EOD

cat >~/.config/systemd/user/looper.timer <

[Timer]

AccuracySec=5

OnUnitActiveSec=5

EOD

1) systemctl --user daemon-reload

2) systemctl --user start looper.timer

   # to have first activation timestamp/sentinel

   systemctl --user start looper.service

o  Observe the service is being regularly triggered.

3) systemctl set-property user@$UID.service TasksMax=2

o  Observe the tight looping as long as the looper.service cannot be started.

Ref: #5969

(cherry picked from commit 204d140c4def364c47d36226e4514a7e077fa196)

(cherry picked from commit fe81f6f734ee46a4877df6dda6e31cdc24c00a3c)

Resolves: #1729230

---

 src/core/timer.c | 2 ++

 1 file changed, 2 insertions(+)

diff --git a/src/core/timer.c b/src/core/timer.c

index d32b007c7c..1d4868643a 100644

--- a/src/core/timer.c

+++ b/src/core/timer.c

@@ -416,6 +416,7 @@ static void timer_enter_waiting(Timer *t, bool initial) {

                                 if (base <= 0)

                                         continue;

+                                base = MAX(base, t->last_trigger.monotonic);

                                 break;

@@ -428,6 +429,7 @@ static void timer_enter_waiting(Timer *t, bool initial) {

                                 if (base <= 0)

                                         continue;

+                                base = MAX(base, t->last_trigger.monotonic);

                                 break;