From 2a0feeb4252cbf1207f45e978fe7eb02bb0182ec Mon Sep 17 00:00:00 2001

From: Kyle Walker <walker.kyle.t@gmail.com>

Date: Thu, 30 Jun 2016 15:12:18 -0400

Subject: [PATCH] manager: Only invoke a single sigchld per unit within a

 cleanup cycle

By default, each iteration of manager_dispatch_sigchld() results in a unit level

sigchld event being invoked. For scope units, this results in a scope_sigchld_event()

which can seemingly stall for workloads that have a large number of PIDs within the

scope. The stall exhibits itself as a SIG_0 being initiated for each u->pids entry

as a result of pid_is_unwaited().

v2:

This patch resolves this condition by only paying to cost of a sigchld in the underlying

scope unit once per sigchld iteration. A new "sigchldgen" member resides within the

Unit struct. The Manager is incremented via the sd event loop, accessed via

sd_event_get_iteration, and the Unit member is set to the same value as the manager each

time that a sigchld event is invoked. If the Manager iteration value and Unit member

match, the sigchld event is not invoked for that iteration.

Cherry-picked from: 36f20ae3b2975e44b6ef17e453ae06a289e9a122

Resolves: #1342173

---

 src/core/manager.c | 13 ++++++++++++-

 src/core/unit.c    |  1 +

 src/core/unit.h    |  3 +++

 3 files changed, 16 insertions(+), 1 deletion(-)

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

index e5226a8a6f..63693b93a6 100644

--- a/src/core/manager.c

+++ b/src/core/manager.c

@@ -1747,14 +1747,25 @@ static int manager_dispatch_notify_fd(sd_event_source *source, int fd, uint32_t

 }

 static void invoke_sigchld_event(Manager *m, Unit *u, siginfo_t *si) {

+        uint64_t iteration;

+        

         assert(m);

         assert(u);

         assert(si);

+        sd_event_get_iteration(m->event, &iteration);

+

         log_unit_debug(u->id, "Child "PID_FMT" belongs to %s", si->si_pid, u->id);

         unit_unwatch_pid(u, si->si_pid);

-        UNIT_VTABLE(u)->sigchld_event(u, si->si_pid, si->si_code, si->si_status);

+

+        if (UNIT_VTABLE(u)->sigchld_event) {

+                if (set_size(u->pids) <= 1 || iteration != u->sigchldgen) {

+                        UNIT_VTABLE(u)->sigchld_event(u, si->si_pid, si->si_code, si->si_status);

+                        u->sigchldgen = iteration;

+                } else

+                        log_debug("%s already issued a sigchld this iteration %llu, skipping. Pids still being watched %d", u->id, iteration, set_size(u->pids));

+        }

 }

 static int manager_dispatch_sigchld(Manager *m) {

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

index d6ead7d672..d62135d878 100644

--- a/src/core/unit.c

+++ b/src/core/unit.c

@@ -94,6 +94,7 @@ Unit *unit_new(Manager *m, size_t size) {

         u->unit_file_state = _UNIT_FILE_STATE_INVALID;

         u->unit_file_preset = -1;

         u->on_failure_job_mode = JOB_REPLACE;

+        u->sigchldgen = 0;

         return u;

 }

diff --git a/src/core/unit.h b/src/core/unit.h

index 0eebc0b891..d936457776 100644

--- a/src/core/unit.h

+++ b/src/core/unit.h

@@ -167,6 +167,9 @@ struct Unit {

          * process SIGCHLD for */

         Set *pids;

+        /* Used in sigchld event invocation to avoid repeat events being invoked */

+        uint64_t sigchldgen;

+

         /* Used during GC sweeps */

         unsigned gc_marker;