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From 9684908410868cb590ad74f4747bdbf9b5790abb Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Mon, 13 Nov 2017 15:08:49 +0100
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Subject: [PATCH] unit: rework a bit how we keep the service fdstore from being
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 destroyed during service restart
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When preparing for a restart we quickly go through the DEAD/INACTIVE
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service state before entering AUTO_RESTART. When doing this, we need to
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make sure we don't destroy the FD store. Previously this was done by
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checking the failure state of the unit, and keeping the FD store around
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when the unit failed, under the assumption that the restart logic will
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then get into action.
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This is not entirely correct howver, as there might be failure states
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that will no result in restarts.
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With this commit we slightly alter the logic: a ref counter for the fd
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store is added, that is increased right before we handle the restart
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logic, and decreased again right-after.
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This should ensure that the fdstore lives exactly as long as it needs.
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Follow-up for f0bfbfac43b7faa68ef1bb2ad659c191b9ec85d2.
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(cherry picked from commit 7eb2a8a1259043e107ebec94e30ed160a93f40a7)
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(cherry picked from commit e2636bde0f07319d0d35262dac6ff2638ba4e598)
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Resolves: #1803802
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---
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 src/core/service.c | 23 ++++++++++++++++++-----
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 src/core/service.h |  1 +
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 src/core/unit.c    | 12 ++++--------
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 src/core/unit.h    |  5 ++---
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 4 files changed, 25 insertions(+), 16 deletions(-)
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diff --git a/src/core/service.c b/src/core/service.c
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index 3c2f69a003..e32cdf4594 100644
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--- a/src/core/service.c
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+++ b/src/core/service.c
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@@ -261,6 +261,9 @@ static void service_fd_store_unlink(ServiceFDStore *fs) {
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 static void service_release_fd_store(Service *s) {
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         assert(s);
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+        if (s->n_keep_fd_store > 0)
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+                return;
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+
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         log_unit_debug(UNIT(s)->id, "Releasing all stored fds");
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         while (s->fd_store)
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                 service_fd_store_unlink(s->fd_store);
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@@ -268,7 +271,7 @@ static void service_release_fd_store(Service *s) {
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         assert(s->n_fd_store == 0);
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 }
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-static void service_release_resources(Unit *u, bool inactive) {
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+static void service_release_resources(Unit *u) {
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         Service *s = SERVICE(u);
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         assert(s);
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@@ -278,8 +281,7 @@ static void service_release_resources(Unit *u, bool inactive) {
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         log_unit_debug(u->id, "Releasing resources.");
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-        if (inactive)
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-                service_release_fd_store(s);
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+        service_release_fd_store(s);
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 }
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 static void service_done(Unit *u) {
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@@ -327,7 +329,7 @@ static void service_done(Unit *u) {
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         s->timer_event_source = sd_event_source_unref(s->timer_event_source);
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-        service_release_resources(u, true);
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+        service_release_resources(u);
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 }
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 static int on_fd_store_io(sd_event_source *e, int fd, uint32_t revents, void *userdata) {
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@@ -1330,6 +1332,10 @@ static void service_enter_dead(Service *s, ServiceResult f, bool allow_restart)
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         if (f != SERVICE_SUCCESS)
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                 s->result = f;
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+        /* Make sure service_release_resources() doesn't destroy our FD store, while we are changing through
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+         * SERVICE_FAILED/SERVICE_DEAD before entering into SERVICE_AUTO_RESTART. */
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+        s->n_keep_fd_store++;
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+
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         service_set_state(s, s->result != SERVICE_SUCCESS ? SERVICE_FAILED : SERVICE_DEAD);
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         if (s->result != SERVICE_SUCCESS) {
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@@ -1351,12 +1357,19 @@ static void service_enter_dead(Service *s, ServiceResult f, bool allow_restart)
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             (!IN_SET(s->main_exec_status.code, CLD_KILLED, CLD_DUMPED) || !set_contains(s->restart_prevent_status.signal, INT_TO_PTR(s->main_exec_status.status)))) {
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                 r = service_arm_timer(s, s->restart_usec);
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-                if (r < 0)
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+                if (r < 0) {
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+                        s->n_keep_fd_store--;
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                         goto fail;
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+                }
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                 service_set_state(s, SERVICE_AUTO_RESTART);
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         }
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+        /* The new state is in effect, let's decrease the fd store ref counter again. Let's also readd us to the GC
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+         * queue, so that the fd store is possibly gc'ed again */
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+        s->n_keep_fd_store--;
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+        unit_add_to_gc_queue(UNIT(s));
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+
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         s->forbid_restart = false;
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         /* We want fresh tmpdirs in case service is started again immediately */
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diff --git a/src/core/service.h b/src/core/service.h
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index 82938a1fc4..e5753f1f4c 100644
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--- a/src/core/service.h
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+++ b/src/core/service.h
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@@ -215,6 +215,7 @@ struct Service {
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         ServiceFDStore *fd_store;
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         unsigned n_fd_store;
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         unsigned n_fd_store_max;
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+        unsigned n_keep_fd_store;
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 };
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 extern const UnitVTable service_vtable;
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diff --git a/src/core/unit.c b/src/core/unit.c
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index 22e31a76b3..eff9fdbe70 100644
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--- a/src/core/unit.c
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+++ b/src/core/unit.c
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@@ -285,7 +285,6 @@ int unit_set_description(Unit *u, const char *description) {
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 bool unit_may_gc(Unit *u) {
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         UnitActiveState state;
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-        bool inactive;
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         assert(u);
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         /* Checks whether the unit is ready to be unloaded for garbage collection.
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@@ -303,17 +302,14 @@ bool unit_may_gc(Unit *u) {
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                 return false;
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         state = unit_active_state(u);
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-        inactive = state == UNIT_INACTIVE;
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-        /* If the unit is inactive and failed and no job is queued for
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-         * it, then release its runtime resources */
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+        /* If the unit is inactive and failed and no job is queued for it, then release its runtime resources */
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         if (UNIT_IS_INACTIVE_OR_FAILED(state) &&
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             UNIT_VTABLE(u)->release_resources)
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-                UNIT_VTABLE(u)->release_resources(u, inactive);
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+                UNIT_VTABLE(u)->release_resources(u);
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-        /* But we keep the unit object around for longer when it is
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-         * referenced or configured to not be gc'ed */
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-        if (!inactive)
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+        /* But we keep the unit object around for longer when it is referenced or configured to not be gc'ed */
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+        if (state != UNIT_INACTIVE)
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                 return false;
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         if (UNIT_VTABLE(u)->no_gc)
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diff --git a/src/core/unit.h b/src/core/unit.h
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index 232be8164f..3b0fd8d9df 100644
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--- a/src/core/unit.h
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+++ b/src/core/unit.h
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@@ -358,9 +358,8 @@ struct UnitVTable {
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          * even though nothing references it and it isn't active in any way. */
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         bool (*may_gc)(Unit *u);
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-        /* When the unit is not running and no job for it queued we
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-         * shall release its runtime resources */
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-        void (*release_resources)(Unit *u, bool inactive);
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+        /* When the unit is not running and no job for it queued we shall release its runtime resources */
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+        void (*release_resources)(Unit *u);
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         /* Return true when this unit is suitable for snapshotting */
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         bool (*check_snapshot)(Unit *u);