From 3bf115ccb9a4096f24dd4c58f1070c918b78eb2a Mon Sep 17 00:00:00 2001 From: Kir Kolyshkin Date: Thu, 12 Dec 2024 17:34:17 -0800 Subject: [PATCH] freeze_processes: implement kludges for cgroup v1 Cgroup v1 freezer has always been problematic, failing to freeze a cgroup. In runc, we have implemented a few kludges to increase the chance of succeeding, but those are used when runc freezes a cgroup for its own purposes (for "runc pause" and to modify device properties for cgroup v1). When criu is used, it fails to freeze a cgroup from time to time (see [1], [2]). Let's try adding kludges similar to ones in runc. Alas, I have absolutely no way to test this, so please review carefully. [1]: https://github.com/opencontainers/runc/issues/4273 [2]: https://github.com/opencontainers/runc/issues/4457 Signed-off-by: Kir Kolyshkin --- criu/seize.c | 32 +++++++++++++++++++++++++++++++- 1 file changed, 31 insertions(+), 1 deletion(-) diff --git a/criu/seize.c b/criu/seize.c index 7ade0b1fe8..67b9c170e4 100644 --- a/criu/seize.c +++ b/criu/seize.c @@ -542,6 +542,7 @@ static int freeze_processes(void) enum freezer_state state = THAWED; static const unsigned long step_ms = 100; + /* Since opts.timeout is in seconds, multiply it by 1000 to convert to milliseconds. */ unsigned long nr_attempts = (opts.timeout * 1000) / step_ms; unsigned long i = 0; @@ -586,6 +587,7 @@ static int freeze_processes(void) * transition stage. */ for (; i <= nr_attempts; i++) { + nanosleep(&req, NULL); state = get_freezer_state(fd); if (state == FREEZER_ERROR) { close(fd); @@ -598,7 +600,35 @@ static int freeze_processes(void) pr_err("Unable to freeze cgroup %s (timed out)\n", opts.freeze_cgroup); goto err; } - nanosleep(&req, NULL); + + if (cgroup_v2) + continue; + + /* As per older kernel docs (freezer-subsystem.txt before + * the kernel commit ef9fe980c6fcc1821), if FREEZING is seen, + * userspace should either retry or thaw. While current + * kernel cgroup v1 docs no longer mention a need to retry, + * even recent kernels can't reliably freeze a cgroup v1. + * + * Let's keep asking the kernel to freeze from time to time. + * In addition, do occasional thaw/sleep/freeze. + * + * This is still a game of chances (the real fix belongs to the kernel) + * but these kludges might improve the probability of success. + * + * Cgroup v2 does not have this problem. + */ + switch (i % 32) { + case 9: + case 20: + freezer_write_state(fd, FROZEN); + break; + case 31: + freezer_write_state(fd, THAWED); + nanosleep(&req, NULL); + freezer_write_state(fd, FROZEN); + break; + } } if (i > nr_attempts) {