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service: make killmode=cgroup|mixed, SendSIGKILL=no services singletons

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KillMode=mixed and control group are used to indicate that all
process should be killed off. SendSIGKILL is used for services
that require a clean shutdown. These are typically database
service where a SigKilled process would result in a lengthy
recovery and who's shutdown or startup time is quite variable
(so Timeout settings aren't of use).

Here we take these two factors and refuse to start a service if
there are existing processes within a control group. Databases,
while generally having some protection against multiple instances
running, lets not stress the rigor of these. Also ExecStartPre
parts of the service aren't as rigoriously written to protect
against against multiple use.

closes #8630
This commit is contained in:
Daniel Black 2019-01-16 21:20:18 +11:00
parent 61a38e0265
commit c53d2d54bd
6 changed files with 52 additions and 17 deletions
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7
man/systemd.kill.xml
View File

@ -139,8 +139,11 @@
<constant>SIGKILL</constant> (or the signal specified by
<varname>FinalKillSignal=</varname>) to remaining processes
after a timeout, if the normal shutdown procedure left
processes of the service around. Takes a boolean value.
Defaults to "yes".
processes of the service around. When disabled, a
<varname>KillMode=</varname> of <constant>control-group</constant>
or <constant>mixed</constant> service will not restart if
processes from prior services exist within the control group.
Takes a boolean value. Defaults to "yes".
</para></listitem>
</varlistentry>

12
src/basic/cgroup-util.c
View File

@ -223,7 +223,7 @@ int cg_kill(
_cleanup_set_free_ Set *allocated_set = NULL;
bool done = false;
int r, ret = 0;
int r, ret = 0, ret_log_kill = 0;
pid_t my_pid;
assert(sig >= 0);
@ -267,7 +267,7 @@ int cg_kill(
continue;
if (log_kill)
log_kill(pid, sig, userdata);
ret_log_kill = log_kill(pid, sig, userdata);
/* If we haven't killed this process yet, kill
* it */
@ -278,8 +278,12 @@ int cg_kill(
if (flags & CGROUP_SIGCONT)
(void) kill(pid, SIGCONT);
if (ret == 0)
ret = 1;
if (ret == 0) {
if (log_kill)
ret = ret_log_kill;
else
ret = 1;
}
}
done = false;

2
src/basic/cgroup-util.h
View File

@ -167,7 +167,7 @@ typedef enum CGroupFlags {
CGROUP_REMOVE = 1 << 2,
} CGroupFlags;
typedef void (*cg_kill_log_func_t)(pid_t pid, int sig, void *userdata);
typedef int (*cg_kill_log_func_t)(pid_t pid, int sig, void *userdata);
int cg_kill(const char *controller, const char *path, int sig, CGroupFlags flags, Set *s, cg_kill_log_func_t kill_log, void *userdata);
int cg_kill_recursive(const char *controller, const char *path, int sig, CGroupFlags flags, Set *s, cg_kill_log_func_t kill_log, void *userdata);

28
src/core/service.c
View File

@ -2006,6 +2006,26 @@ static void service_kill_control_process(Service *s) {
}
}
static int service_adverse_to_leftover_processes(Service *s) {
assert(s);
/* KillMode=mixed and control group are used to indicate that all process should be killed off.
* SendSIGKILL is used for services that require a clean shutdown. These are typically database
* service where a SigKilled process would result in a lengthy recovery and who's shutdown or
* startup time is quite variable (so Timeout settings aren't of use).
*
* Here we take these two factors and refuse to start a service if there are existing processes
* within a control group. Databases, while generally having some protection against multiple
* instances running, lets not stress the rigor of these. Also ExecStartPre parts of the service
* aren't as rigoriously written to protect aganst against multiple use. */
if (unit_warn_leftover_processes(UNIT(s)) &&
IN_SET(s->kill_context.kill_mode, KILL_MIXED, KILL_CONTROL_GROUP) &&
!s->kill_context.send_sigkill) {
return log_unit_error_errno(UNIT(s), SYNTHETIC_ERRNO(EBUSY), "Will not start SendSIGKILL=no service of type KillMode=control-group or mixed while processes exist");
}
return 0;
}
static void service_enter_start(Service *s) {
ExecCommand *c;
usec_t timeout;
@ -2017,7 +2037,9 @@ static void service_enter_start(Service *s) {
service_unwatch_control_pid(s);
service_unwatch_main_pid(s);
unit_warn_leftover_processes(UNIT(s));
r = service_adverse_to_leftover_processes(s);
if (r < 0)
goto fail;
if (s->type == SERVICE_FORKING) {
s->control_command_id = SERVICE_EXEC_START;
@ -2110,7 +2132,9 @@ static void service_enter_start_pre(Service *s) {
s->control_command = s->exec_command[SERVICE_EXEC_START_PRE];
if (s->control_command) {
unit_warn_leftover_processes(UNIT(s));
r = service_adverse_to_leftover_processes(s);
if (r < 0)
goto fail;
s->control_command_id = SERVICE_EXEC_START_PRE;

18
src/core/unit.c
View File

@ -4428,7 +4428,7 @@ int unit_make_transient(Unit *u) {
return 0;
}
static void log_kill(pid_t pid, int sig, void *userdata) {
static int log_kill(pid_t pid, int sig, void *userdata) {
_cleanup_free_ char *comm = NULL;
(void) get_process_comm(pid, &comm);
@ -4436,13 +4436,15 @@ static void log_kill(pid_t pid, int sig, void *userdata) {
/* Don't log about processes marked with brackets, under the assumption that these are temporary processes
only, like for example systemd's own PAM stub process. */
if (comm && comm[0] == '(')
return;
return 0;
log_unit_notice(userdata,
"Killing process " PID_FMT " (%s) with signal SIG%s.",
pid,
strna(comm),
signal_to_string(sig));
return 1;
}
static int operation_to_signal(KillContext *c, KillOperation k) {
@ -5394,29 +5396,31 @@ int unit_prepare_exec(Unit *u) {
return 0;
}
static void log_leftover(pid_t pid, int sig, void *userdata) {
static int log_leftover(pid_t pid, int sig, void *userdata) {
_cleanup_free_ char *comm = NULL;
(void) get_process_comm(pid, &comm);
if (comm && comm[0] == '(') /* Most likely our own helper process (PAM?), ignore */
return;
return 0;
log_unit_warning(userdata,
"Found left-over process " PID_FMT " (%s) in control group while starting unit. Ignoring.\n"
"This usually indicates unclean termination of a previous run, or service implementation deficiencies.",
pid, strna(comm));
return 1;
}
void unit_warn_leftover_processes(Unit *u) {
int unit_warn_leftover_processes(Unit *u) {
assert(u);
(void) unit_pick_cgroup_path(u);
if (!u->cgroup_path)
return;
return 0;
(void) cg_kill_recursive(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, 0, 0, NULL, log_leftover, u);
return cg_kill_recursive(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, 0, 0, NULL, log_leftover, u);
}
bool unit_needs_console(Unit *u) {

2
src/core/unit.h
View File

@ -804,7 +804,7 @@ void unit_unlink_state_files(Unit *u);
int unit_prepare_exec(Unit *u);
void unit_warn_leftover_processes(Unit *u);
int unit_warn_leftover_processes(Unit *u);
bool unit_needs_console(Unit *u);