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From 13bcf85ffab4b4e67039599246604a3f5b503975 Mon Sep 17 00:00:00 2001
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From: David Tardon <dtardon@redhat.com>
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Date: Tue, 24 Apr 2018 15:19:38 +0200
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Subject: [PATCH] fix race between daemon-reload and other commands
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When "systemctl daemon-reload" is run at the same time as "systemctl
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start foo", the latter might hang. That's because commands like start
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wait for JobRemoved signal to know when the job is finished. But if the
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job is finished during reloading, the signal is never sent.
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The hang can be easily reproduced by running
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    # for ((N=1; N>0; N++)) ; do echo $N ; systemctl daemon-reload ; done
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    # for ((N=1; N>0; N++)) ; do echo $N ; systemctl start systemd-coredump.socket ; done
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in two different terminals. The start command will hang after 1-2
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iterations.
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This keeps track of jobs that were started before reload and finished
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during it and sends JobRemoved after the reload has finished.
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(cherry picked from commit a7a7163df7fc8a9f794f6803b2f6c9c9b0745a1f)
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---
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 src/core/job.c     | 45 ++++++++++++++++++++++++++++++++++++++++-----
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 src/core/job.h     |  2 ++
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 src/core/manager.c | 15 +++++++++++++++
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 src/core/manager.h |  3 +++
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 4 files changed, 60 insertions(+), 5 deletions(-)
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diff --git a/src/core/job.c b/src/core/job.c
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index 1861c8a63..275503169 100644
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--- a/src/core/job.c
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+++ b/src/core/job.c
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@@ -53,6 +53,7 @@ Job* job_new_raw(Unit *unit) {
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         j->manager = unit->manager;
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         j->unit = unit;
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         j->type = _JOB_TYPE_INVALID;
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+        j->reloaded = false;
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         return j;
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 }
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@@ -74,7 +75,7 @@ Job* job_new(Unit *unit, JobType type) {
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         return j;
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 }
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-void job_free(Job *j) {
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+void job_unlink(Job *j) {
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         assert(j);
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         assert(!j->installed);
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         assert(!j->transaction_prev);
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@@ -82,13 +83,28 @@ void job_free(Job *j) {
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         assert(!j->subject_list);
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         assert(!j->object_list);
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-        if (j->in_run_queue)
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+        if (j->in_run_queue) {
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                 LIST_REMOVE(run_queue, j->manager->run_queue, j);
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+                j->in_run_queue = false;
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+        }
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-        if (j->in_dbus_queue)
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+        if (j->in_dbus_queue) {
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                 LIST_REMOVE(dbus_queue, j->manager->dbus_job_queue, j);
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+                j->in_dbus_queue = false;
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+        }
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+
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+        j->timer_event_source = sd_event_source_unref(j->timer_event_source);
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+}
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+
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+void job_free(Job *j) {
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+        assert(j);
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+        assert(!j->installed);
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+        assert(!j->transaction_prev);
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+        assert(!j->transaction_next);
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+        assert(!j->subject_list);
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+        assert(!j->object_list);
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-        sd_event_source_unref(j->timer_event_source);
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+        job_unlink(j);
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         sd_bus_track_unref(j->clients);
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         strv_free(j->deserialized_clients);
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@@ -246,6 +262,7 @@ int job_install_deserialized(Job *j) {
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         *pj = j;
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         j->installed = true;
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+        j->reloaded = true;
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         if (j->state == JOB_RUNNING)
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                 j->unit->manager->n_running_jobs++;
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@@ -790,6 +807,19 @@ static void job_emit_status_message(Unit *u, JobType t, JobResult result) {
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                 job_print_status_message(u, t, result);
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 }
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+static int job_save_pending_finished_job(Job *j) {
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+        int r;
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+
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+        assert(j);
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+
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+        r = set_ensure_allocated(&j->manager->pending_finished_jobs, NULL);
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+        if (r < 0)
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+                return r;
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+
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+        job_unlink(j);
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+        return set_put(j->manager->pending_finished_jobs, j);
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+}
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+
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 int job_finish_and_invalidate(Job *j, JobResult result, bool recursive, bool already) {
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         Unit *u;
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         Unit *other;
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@@ -829,7 +859,12 @@ int job_finish_and_invalidate(Job *j, JobResult result, bool recursive, bool alr
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                 j->manager->n_failed_jobs ++;
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         job_uninstall(j);
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-        job_free(j);
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+        /* Remember jobs started before the reload */
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+        if (j->manager->n_reloading > 0 && j->reloaded) {
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+                if (job_save_pending_finished_job(j) < 0)
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+                        job_free(j);
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+        } else
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+                job_free(j);
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         /* Fail depending jobs on failure */
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         if (result != JOB_DONE && recursive) {
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diff --git a/src/core/job.h b/src/core/job.h
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index 535052b48..4ae6f2802 100644
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--- a/src/core/job.h
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+++ b/src/core/job.h
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@@ -172,10 +172,12 @@ struct Job {
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         bool sent_dbus_new_signal:1;
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         bool ignore_order:1;
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         bool irreversible:1;
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+        bool reloaded:1;
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 };
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 Job* job_new(Unit *unit, JobType type);
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 Job* job_new_raw(Unit *unit);
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+void job_unlink(Job *job);
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 void job_free(Job *job);
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 Job* job_install(Job *j);
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 int job_install_deserialized(Job *j);
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diff --git a/src/core/manager.c b/src/core/manager.c
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index 47b09e1e9..9c406bb5b 100644
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--- a/src/core/manager.c
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+++ b/src/core/manager.c
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@@ -2702,6 +2702,18 @@ finish:
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         return r;
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 }
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+static void manager_flush_finished_jobs(Manager *m) {
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+        Job *j;
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+
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+        while ((j = set_steal_first(m->pending_finished_jobs))) {
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+                bus_job_send_removed_signal(j);
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+                job_free(j);
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+        }
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+
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+        set_free(m->pending_finished_jobs);
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+        m->pending_finished_jobs = NULL;
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+}
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+
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 int manager_reload(Manager *m) {
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         int r, q;
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         _cleanup_fclose_ FILE *f = NULL;
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@@ -2784,6 +2796,9 @@ int manager_reload(Manager *m) {
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         assert(m->n_reloading > 0);
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         m->n_reloading--;
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+        if (m->n_reloading <= 0)
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+                manager_flush_finished_jobs(m);
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+
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         m->send_reloading_done = true;
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         return r;
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diff --git a/src/core/manager.h b/src/core/manager.h
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index e91e7bd8b..90d2d982e 100644
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--- a/src/core/manager.h
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+++ b/src/core/manager.h
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@@ -270,6 +270,9 @@ struct Manager {
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         /* non-zero if we are reloading or reexecuting, */
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         int n_reloading;
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+        /* A set which contains all jobs that started before reload and finished
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+         * during it */
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+        Set *pending_finished_jobs;
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         unsigned n_installed_jobs;
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         unsigned n_failed_jobs;