diff --git a/src/libstore/unix/build/local-derivation-goal.cc b/src/libstore/unix/build/local-derivation-goal.cc index 01a133766..d55278a52 100644 --- a/src/libstore/unix/build/local-derivation-goal.cc +++ b/src/libstore/unix/build/local-derivation-goal.cc @@ -444,25 +444,22 @@ void LocalDerivationGoal::startBuilder() #if __linux__ experimentalFeatureSettings.require(Xp::Cgroups); + /* If we're running from the daemon, then this will return the + root cgroup of the service. Otherwise, it will return the + current cgroup. */ + auto rootCgroup = getRootCgroup(); auto cgroupFS = getCgroupFS(); if (!cgroupFS) throw Error("cannot determine the cgroups file system"); - - auto ourCgroups = getCgroups("/proc/self/cgroup"); - auto ourCgroup = ourCgroups[""]; - if (ourCgroup == "") - throw Error("cannot determine cgroup name from /proc/self/cgroup"); - - auto ourCgroupPath = canonPath(*cgroupFS + "/" + ourCgroup); - - if (!pathExists(ourCgroupPath)) - throw Error("expected cgroup directory '%s'", ourCgroupPath); + auto rootCgroupPath = canonPath(*cgroupFS + "/" + rootCgroup); + if (!pathExists(rootCgroupPath)) + throw Error("expected cgroup directory '%s'", rootCgroupPath); static std::atomic counter{0}; cgroup = buildUser - ? fmt("%s/nix-build-uid-%d", ourCgroupPath, buildUser->getUID()) - : fmt("%s/nix-build-pid-%d-%d", ourCgroupPath, getpid(), counter++); + ? fmt("%s/nix-build-uid-%d", rootCgroupPath, buildUser->getUID()) + : fmt("%s/nix-build-pid-%d-%d", rootCgroupPath, getpid(), counter++); debug("using cgroup '%s'", *cgroup); diff --git a/src/libutil/current-process.cc b/src/libutil/current-process.cc index 0bc46d746..ed1c1ca6c 100644 --- a/src/libutil/current-process.cc +++ b/src/libutil/current-process.cc @@ -32,11 +32,7 @@ unsigned int getMaxCPU() auto cgroupFS = getCgroupFS(); if (!cgroupFS) return 0; - auto cgroups = getCgroups("/proc/self/cgroup"); - auto cgroup = cgroups[""]; - if (cgroup == "") return 0; - - auto cpuFile = *cgroupFS + "/" + cgroup + "/cpu.max"; + auto cpuFile = *cgroupFS + "/" + getCurrentCgroup() + "/cpu.max"; auto cpuMax = readFile(cpuFile); auto cpuMaxParts = tokenizeString>(cpuMax, " \n"); diff --git a/src/libutil/linux/cgroup.cc b/src/libutil/linux/cgroup.cc index 140ff4566..ad3e8a017 100644 --- a/src/libutil/linux/cgroup.cc +++ b/src/libutil/linux/cgroup.cc @@ -144,4 +144,23 @@ CgroupStats destroyCgroup(const Path & cgroup) return destroyCgroup(cgroup, true); } +std::string getCurrentCgroup() +{ + auto cgroupFS = getCgroupFS(); + if (!cgroupFS) + throw Error("cannot determine the cgroups file system"); + + auto ourCgroups = getCgroups("/proc/self/cgroup"); + auto ourCgroup = ourCgroups[""]; + if (ourCgroup == "") + throw Error("cannot determine cgroup name from /proc/self/cgroup"); + return ourCgroup; +} + +std::string getRootCgroup() +{ + static std::string rootCgroup = getCurrentCgroup(); + return rootCgroup; +} + } diff --git a/src/libutil/linux/cgroup.hh b/src/libutil/linux/cgroup.hh index 783a0ab87..87d135ba6 100644 --- a/src/libutil/linux/cgroup.hh +++ b/src/libutil/linux/cgroup.hh @@ -25,4 +25,13 @@ struct CgroupStats */ CgroupStats destroyCgroup(const Path & cgroup); +std::string getCurrentCgroup(); + +/** + * Get the cgroup that should be used as the parent when creating new + * sub-cgroups. The first time this is called, the current cgroup will be + * returned, and then all subsequent calls will return the original cgroup. + */ +std::string getRootCgroup(); + } diff --git a/src/nix/unix/daemon.cc b/src/nix/unix/daemon.cc index 66d8dbcf0..746963a01 100644 --- a/src/nix/unix/daemon.cc +++ b/src/nix/unix/daemon.cc @@ -33,6 +33,10 @@ #include #include +#if __linux__ +#include "cgroup.hh" +#endif + #if __APPLE__ || __FreeBSD__ #include #endif @@ -312,6 +316,27 @@ static void daemonLoop(std::optional forceTrustClientOpt) // Get rid of children automatically; don't let them become zombies. setSigChldAction(true); + #if __linux__ + if (settings.useCgroups) { + experimentalFeatureSettings.require(Xp::Cgroups); + + // This also sets the root cgroup to the current one. + auto rootCgroup = getRootCgroup(); + auto cgroupFS = getCgroupFS(); + if (!cgroupFS) + throw Error("cannot determine the cgroups file system"); + auto rootCgroupPath = canonPath(*cgroupFS + "/" + rootCgroup); + if (!pathExists(rootCgroupPath)) + throw Error("expected cgroup directory '%s'", rootCgroupPath); + auto daemonCgroupPath = rootCgroupPath + "/nix-daemon"; + // Create new sub-cgroup for the daemon. + if (mkdir(daemonCgroupPath.c_str(), 0755) != 0 && errno != EEXIST) + throw SysError("creating cgroup '%s'", daemonCgroupPath); + // Move daemon into the new cgroup. + writeFile(daemonCgroupPath + "/cgroup.procs", fmt("%d", getpid())); + } + #endif + // Loop accepting connections. while (1) { diff --git a/tests/nixos/cgroups/default.nix b/tests/nixos/cgroups/default.nix new file mode 100644 index 000000000..b8febbf4b --- /dev/null +++ b/tests/nixos/cgroups/default.nix @@ -0,0 +1,40 @@ +{ nixpkgs, ... }: + +{ + name = "cgroups"; + + nodes = + { + host = + { config, pkgs, ... }: + { virtualisation.additionalPaths = [ pkgs.stdenvNoCC ]; + nix.extraOptions = + '' + extra-experimental-features = nix-command auto-allocate-uids cgroups + extra-system-features = uid-range + ''; + nix.settings.use-cgroups = true; + nix.nixPath = [ "nixpkgs=${nixpkgs}" ]; + }; + }; + + testScript = { nodes }: '' + start_all() + + host.wait_for_unit("multi-user.target") + + # Start build in background + host.execute("NIX_REMOTE=daemon nix build --auto-allocate-uids --file ${./hang.nix} >&2 &") + service = "/sys/fs/cgroup/system.slice/nix-daemon.service" + + # Wait for cgroups to be created + host.succeed(f"until [ -e {service}/nix-daemon ]; do sleep 1; done", timeout=30) + host.succeed(f"until [ -e {service}/nix-build-uid-* ]; do sleep 1; done", timeout=30) + + # Check that there aren't processes where there shouldn't be, and that there are where there should be + host.succeed(f'[ -z "$(cat {service}/cgroup.procs)" ]') + host.succeed(f'[ -n "$(cat {service}/nix-daemon/cgroup.procs)" ]') + host.succeed(f'[ -n "$(cat {service}/nix-build-uid-*/cgroup.procs)" ]') + ''; + +} diff --git a/tests/nixos/cgroups/hang.nix b/tests/nixos/cgroups/hang.nix new file mode 100644 index 000000000..cefe2d031 --- /dev/null +++ b/tests/nixos/cgroups/hang.nix @@ -0,0 +1,10 @@ +{ }: + +with import {}; + +runCommand "hang" + { requiredSystemFeatures = "uid-range"; + } + '' + sleep infinity + '' diff --git a/tests/nixos/default.nix b/tests/nixos/default.nix index 40d29b371..62fc6b10f 100644 --- a/tests/nixos/default.nix +++ b/tests/nixos/default.nix @@ -157,4 +157,6 @@ in s3-binary-cache-store = runNixOSTestFor "x86_64-linux" ./s3-binary-cache-store.nix; fsync = runNixOSTestFor "x86_64-linux" ./fsync.nix; + + cgroups = runNixOSTestFor "x86_64-linux" ./cgroups; }