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core: do BindMount/MountImage operations in async control process

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These operations might require slow I/O, and thus might block PID1's main
loop for an undeterminated amount of time. Instead of performing them
inline, fork a worker process and stash away the D-Bus message, and reply
once we get a SIGCHILD indicating they have completed. That way we don't
break compatibility and callers can continue to rely on the fact that when
they get the method reply the operation either succeeded or failed.

To keep backward compatibility, unlike reload control processes, these
are ran inside init.scope and not the target cgroup. Unlike ExecReload,
this is under our control and is not defined by the unit. This is necessary
because previously the operation also wasn't ran from the target cgroup,
so suddenly forking a copy-on-write copy of pid1 into the target cgroup
will make memory usage spike, and if there is a MemoryMax= or MemoryHigh=
set and the cgroup is already close to the limit, it will cause an OOM
kill, where previously it would have worked fine.
This commit is contained in:
Luca Boccassi
2024-08-29 12:48:55 +01:00
committed by Luca Boccassi
parent 5121f7c45b
commit 5162829ec8
25 changed files with 480 additions and 146 deletions
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src/core/socket.c
+3 -3
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@@ -1568,7 +1568,7 @@ static int socket_address_listen_in_cgroup(
if (socketpair(AF_UNIX, SOCK_SEQPACKET|SOCK_CLOEXEC, 0, pair) < 0)
return log_unit_error_errno(UNIT(s), errno, "Failed to create communication channel: %m");
r = unit_fork_helper_process(UNIT(s), "(sd-listen)", &pid);
r = unit_fork_helper_process(UNIT(s), "(sd-listen)", /* into_cgroup= */ true, &pid);
if (r < 0)
return log_unit_error_errno(UNIT(s), r, "Failed to fork off listener stub process: %m");
if (r == 0) {
@@ -1989,7 +1989,7 @@ static int socket_chown(Socket *s, PidRef *ret_pid) {
/* We have to resolve the user names out-of-process, hence
* let's fork here. It's messy, but well, what can we do? */
r = unit_fork_helper_process(UNIT(s), "(sd-chown)", &pid);
r = unit_fork_helper_process(UNIT(s), "(sd-chown)", /* into_cgroup= */ true, &pid);
if (r < 0)
return r;
if (r == 0) {
@@ -3013,7 +3013,7 @@ static int socket_accept_in_cgroup(Socket *s, SocketPort *p, int fd) {
if (socketpair(AF_UNIX, SOCK_SEQPACKET|SOCK_CLOEXEC, 0, pair) < 0)
return log_unit_error_errno(UNIT(s), errno, "Failed to create communication channel: %m");
r = unit_fork_helper_process(UNIT(s), "(sd-accept)", &pid);
r = unit_fork_helper_process(UNIT(s), "(sd-accept)", /* into_cgroup= */ true, &pid);
if (r < 0)
return log_unit_error_errno(UNIT(s), r, "Failed to fork off accept stub process: %m");
if (r == 0) {