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I checked all the sources, I don't understand how this could happen since s->control_command and s->control_command_id are "bound" together:
when s->control_command_id is changed to _SERVICE_EXEC_COMMAND_INVALID, s->control_command is always set to NULL.
But from the coredump, this wasn't the case.
I'm trying to set up a reproducer but failed so far.
I believe a condition would be to have a reload while a ExecStartPost executes.
Additionally at least ExecStartPost are required and the 2nd one should execute at the time of the reload.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (Low: systemd security and bug fix update), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHSA-2020:4007
Description of problem: Systemd segfaults after or while reloading systemd segfaults reloading "kernel: systemd[1]: segfault at 48 ip 000055e3aedd0e68 sp 00007ffedf6a04a0 error 4 in systemd[55e3aed93000+163000]" [rhel-7.7] Version-Release number of selected component (if applicable): $ grep systemd installed-rpms systemd-219-67.el7_7.3.x86_64 Wed Mar 25 21:38:12 2020 systemd-libs-219-67.el7_7.3.i686 Wed Mar 25 21:38:25 2020 systemd-libs-219-67.el7_7.3.x86_64 Wed Mar 25 21:38:11 2020 systemd-python-219-67.el7_7.3.x86_64 Wed Mar 25 21:38:18 2020 systemd-sysv-219-67.el7_7.3.x86_64 Wed Mar 25 21:38:13 2020 How reproducible: Customer tell us the problem repeats itself now and then and provided a core. Steps to Reproduce: 1. 2. 3. Actual results: Expected results: Additional info: journald extract: Apr 27 01:02:03 hostname systemd[1]: Reloading. Apr 27 01:02:03 hostname systemd[1]: Starting Insights Client... Apr 27 01:02:03 hostname systemd[1]: Reloading. Apr 27 01:02:03 hostname systemd[1]: Reloading. Apr 27 01:02:03 hostname kernel: systemd[1]: segfault at 48 ip 000055e3aedd0e68 sp 00007ffedf6a04a0 error 4 in systemd[55e3aed93000+163000] Apr 27 01:02:03 hostname abrt-hook-ccpp[4278]: Only 885MiB is available on /var/spool/abrt Apr 27 01:02:03 hostname abrt-hook-ccpp[4278]: Process 4277 (systemd) of user 0 killed by SIGSEGV - ignoring (low free space) Apr 27 01:02:03 hostname abrt-hook-ccpp[4278]: Saved core dump of pid 4277 to core.4277 at / (19238912 bytes) Apr 27 01:02:03 hostname systemd[1]: Caught <SEGV>, dumped core as pid 4277. Apr 27 01:02:03 hostname systemd[1]: Freezing execution. Apr 27 01:02:11 hostname insights-client[4256]: Starting to collect Insights data for some.hostname.net Apr 27 01:02:11 hostname insights-client[4256]: Failed to notify init system: Connection refused [..] Apr 27 01:02:26 hostname insights-client[4256]: Failed to notify init system: Connection refused Apr 27 01:02:28 hostname dbus[1712]: [system] Failed to activate service 'org.freedesktop.systemd1': timed out Additional information from RMetrich: Coredump Analysis We have systemd dying while reloading: -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- (gdb) bt #0 0x00007f1645682647 in kill () at ../sysdeps/unix/syscall-template.S:81 #1 0x000055e3aedb996d in crash (sig=11) at src/core/main.c:172 #2 <signal handler called> #3 0x000055e3aedd0e68 in service_exec_command_index (current=0x55e3b0afadf0, id=_SERVICE_EXEC_COMMAND_INVALID, u=0x55e3b0b69640) at src/core/service.c:2033 #4 service_serialize_exec_command (u=u@entry=0x55e3b0b69640, f=f@entry=0x55e3b0afe1f0, command=0x55e3b0afadf0) at src/core/service.c:2063 #5 0x000055e3aedd1277 in service_serialize (u=0x55e3b0b69640, f=0x55e3b0afe1f0, fds=0x55e3b0c25070) at src/core/service.c:2122 #6 0x000055e3aee67626 in unit_serialize (u=u@entry=0x55e3b0b69640, f=f@entry=0x55e3b0afe1f0, fds=fds@entry=0x55e3b0c25070, serialize_jobs=serialize_jobs@entry=true) at src/core/unit.c:2561 #7 0x000055e3aedbf962 in manager_serialize (m=m@entry=0x55e3b0aed040, f=0x55e3b0afe1f0, fds=fds@entry=0x55e3b0c25070, switching_root=switching_root@entry=false) at src/core/manager.c:2553 #8 0x000055e3aedc0998 in manager_reload (m=m@entry=0x55e3b0aed040) at src/core/manager.c:2792 #9 0x000055e3aedb6c5f in main (argc=5, argv=0x7ffedf6a1038) at src/core/main.c:1799 -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- Upon reload, systemd "serializes" the internal state. Here, it was serializing "insights-client.service": -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- (gdb) f 4 #4 service_serialize_exec_command (u=u@entry=0x55e3b0b69640, f=f@entry=0x55e3b0afe1f0, command=0x55e3b0afadf0) at src/core/service.c:2063 2063 idx = service_exec_command_index(u, id, command); (gdb) p s->main_pid $1 = 4256 (gdb) p u->id $2 = 0x55e3b0c46260 "insights-client.service" -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- systemd died while serializing ExecStartPost's 2nd command: " ExecStartPost=/bin/bash -c "if [ -d /sys/fs/cgroup/memory ]; then echo 1G > /sys/fs/cgroup/memory/system.slice/insights-client.service/memory.soft_limit_in_bytes; fi" " -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- (gdb) p command->argv[0] $5 = 0x55e3b0b51860 "/bin/bash" (gdb) p command->argv[1] $6 = 0x55e3b0b69f60 "-c" (gdb) p command->argv[2] $7 = 0x55e3b0b69f80 "if [ -d /sys/fs/cgroup/memory ]; then echo 1G > /sys/fs/cgroup/memory/system.slice/insights-client.service/memory.soft_limit_in_bytes; fi" -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- Relevant source code: -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- 2039 static int service_serialize_exec_command(Unit *u, FILE *f, ExecCommand *command) { 2040 Service *s = SERVICE(u); 2041 ServiceExecCommand id; 2042 unsigned idx; 2043 const char *type; 2044 char **arg; 2045 _cleanup_strv_free_ char **escaped_args = NULL; 2046 _cleanup_free_ char *args = NULL, *p = NULL; 2047 size_t allocated = 0, length = 0; 2048 2049 assert(s); 2050 assert(f); 2051 2052 if (!command) 2053 return 0; 2054 2055 if (command == s->control_command) { 2056 type = "control"; 2057 id = s->control_command_id; 2058 } else { 2059 type = "main"; 2060 id = SERVICE_EXEC_START; 2061 } 2062 2063 idx = service_exec_command_index(u, id, command); <--- HERE 2023 static unsigned service_exec_command_index(Unit *u, ServiceExecCommand id, ExecCommand *current) { 2024 Service *s = SERVICE(u); 2025 unsigned idx = 0; 2026 ExecCommand *first, *c; 2027 2028 assert(s); 2029 2030 first = s->exec_command[id]; <--- HERE 'first' is invalid 2031 2032 /* Figure out where we are in the list by walking back to the beginning */ 2033 for (c = current; c != first; c = c->command_prev) <--- HERE 2034 idx++; 2035 2036 return idx; 2037 } -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- Why it died? Because the "s->control_command_id" was not expected: -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- (gdb) p s->control_command_id $8 = _SERVICE_EXEC_COMMAND_INVALID (gdb) p id $9 = _SERVICE_EXEC_COMMAND_INVALID -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- This caused the called function "service_exec_command_index" to derefence a NULL pointer: -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- (gdb) down #3 0x000055e3aedd0e68 in service_exec_command_index (current=0x55e3b0afadf0, id=_SERVICE_EXEC_COMMAND_INVALID, u=0x55e3b0b69640) at src/core/service.c:2033 2033 for (c = current; c != first; c = c->command_prev) (gdb) p current $10 = (ExecCommand *) 0x55e3b0afadf0 (gdb) p c $11 = (ExecCommand *) 0x0 (gdb) p first $12 = (ExecCommand *) 0x55e3b0c48300 (gdb) p *first $13 = {path = 0x1 <Address 0x1 out of bounds>, argv = 0x55e3b0aed4e0, exec_status = {start_timestamp = { realtime = 94436410693184, monotonic = 0}, exit_timestamp = {realtime = 0, monotonic = 227}, pid = 100, code = 0, status = -1}, command_next = 0x0, command_prev = 0x0, ignore = 64} -------- 8< ---------------- 8< ---------------- 8< ---------------- 8< -------- We have 'c' now NULL and anyway 'first' was pointing to invalid memory. What remains to understand is when this could happen.