On Mon, Mar 03, 2014 at 04:39:00PM -0600, Serge Hallyn wrote: > 1. remove the cgm_dbus_disconnected handler. We're using a proxy > anyway, and not keeping it around. > > 2. comment most of the cgm functions to describe when they are called, to > ease locking review > > 3. the cgmanager mutex is now held for the duration of a connection, from > cgm_dbus_connect to cgm_dbus_disconnect. > > 3b. so remove the mutex lock/unlock from functions which are called during > container startup with the cgmanager connection already up > > 4. remove the cgroup_restart(). It's no longer needed since we don't > daemonize while we have the cgmanager socket open. > > 5. report errors and return early if cgm_dbus_connect() fails > > 6. don't keep the cgm connection open after cgm_ops_init. I'm a bit torn > on this one as it means that things like lxc-start will always connect > twice. But if we do this there is no good answer, given threaded API > users, on when to drop that initial connection. > > 7. cgm_unfreeze and nrtasks: grab the dbus connection, as we'll never > have it at that point. (technically i doubt anyone will use > cgmanager and utmp helper on the same host :) > > 8. lxc_spawn: make sure we only disconnect cgroups if they were already > connected. >
The change looks fine to me though it still looks fragile and I think
I'd be much happier with all cgm_ functions always calling
cgm_dbus_connect and cgm_dbus_disconnect and just have those do the
right thing.
cgm_dbus_{dis}connect would just look for a global cgm_keep_connected
bool which we'd set to true before initialization and set to false after
the container is ready.
So long as this is set to true, any call to cgm_dbus_connect will check
whether we have a connection, if we do, it'll just return, if we don't,
it'll establish one. Calls to cgm_dbus_disconnect would turn into no-ops
unless cgm_keep_connected is set to false, which we'd do just before
calling a final cgm_dbus_disconnect once we're done setting up the
container.
That way if at some random point in the future we decide to use one of
the cgm_ functions somewhere else in the code, we won't get into weird
behaviors that we didn't think about.
> Signed-off-by: Serge Hallyn <[email protected]>
> ---
> src/lxc/cgmanager.c | 143
> ++++++++++++++++++++++++++++++-------------------
> src/lxc/cgroup.c | 8 ---
> src/lxc/cgroup.h | 1 -
> src/lxc/lxccontainer.c | 1 -
> src/lxc/start.c | 6 +++
> 5 files changed, 95 insertions(+), 64 deletions(-)
>
> diff --git a/src/lxc/cgmanager.c b/src/lxc/cgmanager.c
> index 7be94a7..c95b3d0 100644
> --- a/src/lxc/cgmanager.c
> +++ b/src/lxc/cgmanager.c
> @@ -95,14 +95,13 @@ static char **subsystems;
> static DBusConnection *connection;
>
> #define CGMANAGER_DBUS_SOCK "unix:path=/sys/fs/cgroup/cgmanager/sock"
> -static void cgm_dbus_disconnected(DBusConnection *connection);
> static bool cgm_dbus_connect(void)
> {
> DBusError dbus_error;
> dbus_error_init(&dbus_error);
>
> lock_mutex(&thread_mutex);
> - connection = nih_dbus_connect(CGMANAGER_DBUS_SOCK,
> cgm_dbus_disconnected);
> + connection = nih_dbus_connect(CGMANAGER_DBUS_SOCK, NULL);
> if (!connection) {
> NihError *nerr;
> nerr = nih_error_get();
> @@ -134,36 +133,20 @@ static bool cgm_dbus_connect(void)
> ERROR("Error pinging cgroup manager: %s", nerr->message);
> nih_free(nerr);
> }
> - unlock_mutex(&thread_mutex);
> return true;
> }
>
> static void cgm_dbus_disconnect(void)
> {
> - lock_mutex(&thread_mutex);
> if (cgroup_manager)
> nih_free(cgroup_manager);
> cgroup_manager = NULL;
> - dbus_connection_unref(connection);
> + if (connection)
> + dbus_connection_unref(connection);
> connection = NULL;
> unlock_mutex(&thread_mutex);
> }
>
> -static void cgm_dbus_disconnected(DBusConnection *connection)
> -{
> - lock_mutex(&thread_mutex);
> - WARN("Cgroup manager connection was terminated");
> - cgroup_manager = NULL;
> - dbus_connection_unref(connection);
> - connection = NULL;
> - unlock_mutex(&thread_mutex);
> - if (cgm_dbus_connect()) {
> - INFO("New cgroup manager connection was opened");
> - } else {
> - WARN("Cgroup manager unable to re-open connection");
> - }
> -}
> -
> static int send_creds(int sock, int rpid, int ruid, int rgid)
> {
> struct msghdr msg = { 0 };
> @@ -200,9 +183,11 @@ static int send_creds(int sock, int rpid, int ruid, int
> rgid)
> return 0;
> }
>
> +/*
> + * Called during container startup. The cgmanager socket is open
> + */
> static bool lxc_cgmanager_create(const char *controller, const char
> *cgroup_path, int32_t *existed)
> {
> - lock_mutex(&thread_mutex);
> if ( cgmanager_create_sync(NULL, cgroup_manager, controller,
> cgroup_path, existed) != 0) {
> NihError *nerr;
> @@ -210,11 +195,9 @@ static bool lxc_cgmanager_create(const char *controller,
> const char *cgroup_path
> ERROR("call to cgmanager_create_sync failed: %s",
> nerr->message);
> nih_free(nerr);
> ERROR("Failed to create %s:%s", controller, cgroup_path);
> - unlock_mutex(&thread_mutex);
> return false;
> }
>
> - unlock_mutex(&thread_mutex);
> return true;
> }
>
> @@ -222,7 +205,6 @@ static bool lxc_cgmanager_escape(void)
> {
> pid_t me = getpid();
> int i;
> - lock_mutex(&thread_mutex);
> for (i = 0; i < nr_subsystems; i++) {
> if (cgmanager_move_pid_abs_sync(NULL, cgroup_manager,
> subsystems[i], "/", me) != 0) {
> @@ -231,12 +213,10 @@ static bool lxc_cgmanager_escape(void)
> ERROR("call to cgmanager_move_pid_abs_sync(%s) failed:
> %s",
> subsystems[i], nerr->message);
> nih_free(nerr);
> - unlock_mutex(&thread_mutex);
> return false;
> }
> }
>
> - unlock_mutex(&thread_mutex);
> return true;
> }
>
> @@ -254,7 +234,6 @@ static int do_chown_cgroup(const char *controller, const
> char *cgroup_path,
>
> uid_t caller_nsuid = get_ns_uid(origuid);
>
> - lock_mutex(&thread_mutex);
> if (socketpair(AF_UNIX, SOCK_DGRAM, 0, sv) < 0) {
> SYSERROR("Error creating socketpair");
> goto out;
> @@ -316,7 +295,6 @@ static int do_chown_cgroup(const char *controller, const
> char *cgroup_path,
> out:
> close(sv[0]);
> close(sv[1]);
> - unlock_mutex(&thread_mutex);
> if (ret == 1 && *buf == '1')
> return 0;
> return -1;
> @@ -335,23 +313,26 @@ static int chown_cgroup_wrapper(void *data)
> return do_chown_cgroup(arg->controller, arg->cgroup_path, arg->origuid);
> }
>
> +/*
> + * Called during container startup. The cgmanager socket is open
> + */
> static bool lxc_cgmanager_chmod(const char *controller,
> const char *cgroup_path, const char *file, int mode)
> {
> - lock_mutex(&thread_mutex);
> if (cgmanager_chmod_sync(NULL, cgroup_manager, controller,
> cgroup_path, file, mode) != 0) {
> NihError *nerr;
> nerr = nih_error_get();
> ERROR("call to cgmanager_chmod_sync failed: %s", nerr->message);
> nih_free(nerr);
> - unlock_mutex(&thread_mutex);
> return false;
> }
> - unlock_mutex(&thread_mutex);
> return true;
> }
>
> +/*
> + * Called during container startup. The cgmanager socket is open
> + */
> static bool chown_cgroup(const char *controller, const char *cgroup_path,
> struct lxc_conf *conf)
> {
> @@ -384,26 +365,30 @@ static bool chown_cgroup(const char *controller, const
> char *cgroup_path,
> static void cgm_remove_cgroup(const char *controller, const char *path)
> {
> int existed;
> - lock_mutex(&thread_mutex);
> if ( cgmanager_remove_sync(NULL, cgroup_manager, controller,
> path, CG_REMOVE_RECURSIVE, &existed) != 0) {
> NihError *nerr;
> nerr = nih_error_get();
> ERROR("call to cgmanager_remove_sync failed: %s",
> nerr->message);
> nih_free(nerr);
> - unlock_mutex(&thread_mutex);
> ERROR("Error removing %s:%s", controller, path);
> }
> - unlock_mutex(&thread_mutex);
> if (existed == -1)
> INFO("cgroup removal attempt: %s:%s did not exist", controller,
> path);
> }
>
> +/*
> + * We are starting up a container. We open the cgmanager socket, and leave
> it
> + * open (and mutex held) for the rest of container startup.
> + */
> static void *cgm_init(const char *name)
> {
> struct cgm_data *d;
>
> - cgm_dbus_connect();
> + if (!cgm_dbus_connect()) {
> + ERROR("Error connecting to cgroup manager");
> + return NULL;
> + }
> d = malloc(sizeof(*d));
> if (!d)
> return NULL;
> @@ -429,6 +414,10 @@ err1:
> return NULL;
> }
>
> +/*
> + * Called after a failed container startup. The cgmanager socket was just
> + * closed at end of lxc_spawn. We need to re-open
> + */
> static void cgm_destroy(void *hdata)
> {
> struct cgm_data *d = hdata;
> @@ -436,7 +425,10 @@ static void cgm_destroy(void *hdata)
>
> if (!d)
> return;
> - cgm_dbus_connect();
> + if (!cgm_dbus_connect()) {
> + ERROR("Error connecting to cgroup manager");
> + return;
> + }
> for (i = 0; i < nr_subsystems; i++)
> cgm_remove_cgroup(subsystems[i], d->cgroup_path);
>
> @@ -457,6 +449,9 @@ static inline void cleanup_cgroups(char *path)
> cgm_remove_cgroup(subsystems[i], path);
> }
>
> +/*
> + * Called during container startup. The cgmanager socket is open
> + */
> static inline bool cgm_create(void *hdata)
> {
> struct cgm_data *d = hdata;
> @@ -527,17 +522,14 @@ next:
> static bool lxc_cgmanager_enter(pid_t pid, const char *controller,
> const char *cgroup_path)
> {
> - lock_mutex(&thread_mutex);
> if (cgmanager_move_pid_sync(NULL, cgroup_manager, controller,
> cgroup_path, pid) != 0) {
> NihError *nerr;
> nerr = nih_error_get();
> ERROR("call to cgmanager_move_pid_sync failed: %s",
> nerr->message);
> nih_free(nerr);
> - unlock_mutex(&thread_mutex);
> return false;
> }
> - unlock_mutex(&thread_mutex);
> return true;
> }
>
> @@ -552,6 +544,9 @@ static bool do_cgm_enter(pid_t pid, const char
> *cgroup_path)
> return true;
> }
>
> +/*
> + * called during container startup. cgmanager socket is open
> + */
> static inline bool cgm_enter(void *hdata, pid_t pid)
> {
> struct cgm_data *d = hdata;
> @@ -570,6 +565,11 @@ static const char *cgm_get_cgroup(void *hdata, const
> char *subsystem)
> return d->cgroup_path;
> }
>
> +/*
> + * nrtasks is called by the utmp helper by the container monitor.
> + * cgmanager socket was closed after cgroup setup was complete, so we need
> + * to reopen here.
> + */
> static int cgm_get_nrtasks(void *hdata)
> {
> struct cgm_data *d = hdata;
> @@ -579,21 +579,28 @@ static int cgm_get_nrtasks(void *hdata)
> if (!d || !d->cgroup_path)
> return false;
>
> - lock_mutex(&thread_mutex);
> + if (!cgm_dbus_connect()) {
> + ERROR("Error connecting to cgroup manager");
> + return false;
> + }
> if (cgmanager_get_tasks_sync(NULL, cgroup_manager, subsystems[0],
> d->cgroup_path, &pids, &pids_len) != 0) {
> NihError *nerr;
> nerr = nih_error_get();
> ERROR("call to cgmanager_get_tasks_sync failed: %s",
> nerr->message);
> nih_free(nerr);
> - unlock_mutex(&thread_mutex);
> + cgm_dbus_disconnect();
> return -1;
> }
> - unlock_mutex(&thread_mutex);
> nih_free(pids);
> + cgm_dbus_disconnect();
> return pids_len;
> }
>
> +/*
> + * cgm_get is called to get container cgroup settings. cgmanager is not
> + * connected.
> + */
> static int cgm_get(const char *filename, char *value, size_t len, const char
> *name, const char *lxcpath)
> {
> char *result, *controller, *key, *cgroup;
> @@ -610,8 +617,11 @@ static int cgm_get(const char *filename, char *value,
> size_t len, const char *na
> cgroup = lxc_cmd_get_cgroup_path(name, lxcpath, controller);
> if (!cgroup)
> return -1;
> - cgm_dbus_connect();
> - lock_mutex(&thread_mutex);
> + if (!cgm_dbus_connect()) {
> + ERROR("Error connecting to cgroup manager");
> + free(cgroup);
> + return -1;
> + }
> if (cgmanager_get_value_sync(NULL, cgroup_manager, controller, cgroup,
> filename, &result) != 0) {
> /*
> * must consume the nih error
> @@ -622,11 +632,9 @@ static int cgm_get(const char *filename, char *value,
> size_t len, const char *na
> nerr = nih_error_get();
> nih_free(nerr);
> free(cgroup);
> - unlock_mutex(&thread_mutex);
> cgm_dbus_disconnect();
> return -1;
> }
> - unlock_mutex(&thread_mutex);
> cgm_dbus_disconnect();
> free(cgroup);
> newlen = strlen(result);
> @@ -653,7 +661,6 @@ static int cgm_do_set(const char *controller, const char
> *file,
> const char *cgroup, const char *value)
> {
> int ret;
> - lock_mutex(&thread_mutex);
> ret = cgmanager_set_value_sync(NULL, cgroup_manager, controller,
> cgroup, file, value);
> if (ret != 0) {
> @@ -663,10 +670,12 @@ static int cgm_do_set(const char *controller, const
> char *file,
> nih_free(nerr);
> ERROR("Error setting cgroup %s limit %s", file, cgroup);
> }
> - unlock_mutex(&thread_mutex);
> return ret;
> }
>
> +/*
> + * cgm_set is called to change cgroup settings. cgmanager is not connected
> + */
> static int cgm_set(const char *filename, const char *value, const char
> *name, const char *lxcpath)
> {
> char *controller, *key, *cgroup;
> @@ -686,7 +695,11 @@ static int cgm_set(const char *filename, const char
> *value, const char *name, co
> controller, lxcpath, name);
> return -1;
> }
> - cgm_dbus_connect();
> + if (!cgm_dbus_connect()) {
> + ERROR("Error connecting to cgroup manager");
> + free(cgroup);
> + return -1;
> + }
> ret = cgm_do_set(controller, filename, cgroup, value);
> cgm_dbus_disconnect();
> free(cgroup);
> @@ -759,6 +772,11 @@ out_free:
> return false;
> }
>
> +/*
> + * called during cgroup.c:cgroup_ops_init(), at startup. No threads.
> + * We check whether we can talk to cgmanager, escape to root cgroup if
> + * we are root, then close the connection.
> + */
> struct cgroup_ops *cgm_ops_init(void)
> {
> if (!collect_subsytems())
> @@ -767,8 +785,11 @@ struct cgroup_ops *cgm_ops_init(void)
> goto err1;
>
> // root; try to escape to root cgroup
> - if (geteuid() == 0 && !lxc_cgmanager_escape())
> + if (geteuid() == 0 && !lxc_cgmanager_escape()) {
> + cgm_dbus_disconnect();
> goto err2;
> + }
> + cgm_dbus_disconnect();
>
> return &cgmanager_ops;
>
> @@ -779,6 +800,10 @@ err1:
> return NULL;
> }
>
> +/*
> + * unfreeze is called by the command api after killing a container.
> + * cgmanager is not connected.
> + */
> static bool cgm_unfreeze(void *hdata)
> {
> struct cgm_data *d = hdata;
> @@ -786,7 +811,10 @@ static bool cgm_unfreeze(void *hdata)
> if (!d || !d->cgroup_path)
> return false;
>
> - lock_mutex(&thread_mutex);
> + if (!cgm_dbus_connect()) {
> + ERROR("Error connecting to cgroup manager");
> + return false;
> + }
> if (cgmanager_set_value_sync(NULL, cgroup_manager, "freezer",
> d->cgroup_path,
> "freezer.state", "THAWED") != 0) {
> NihError *nerr;
> @@ -794,13 +822,17 @@ static bool cgm_unfreeze(void *hdata)
> ERROR("call to cgmanager_set_value_sync failed: %s",
> nerr->message);
> nih_free(nerr);
> ERROR("Error unfreezing %s", d->cgroup_path);
> - unlock_mutex(&thread_mutex);
> + cgm_dbus_disconnect();
> return false;
> }
> - unlock_mutex(&thread_mutex);
> + cgm_dbus_disconnect();
> return true;
> }
>
> +/*
> + * setup_limits is called during startup. cgmanager is connected, and mutex
> + * is held
> + */
> static bool cgm_setup_limits(void *hdata, struct lxc_list *cgroup_settings,
> bool do_devices)
> {
> struct cgm_data *d = hdata;
> @@ -888,7 +920,10 @@ static bool cgm_attach(const char *name, const char
> *lxcpath, pid_t pid)
> goto out;
> }
>
> - cgm_dbus_connect();
> + if (!cgm_dbus_connect()) {
> + ERROR("Error connecting to cgroup manager");
> + goto out;
> + }
> if (!(pass = do_cgm_enter(pid, cgroup)))
> ERROR("Failed to enter group %s", cgroup);
> cgm_dbus_disconnect();
> diff --git a/src/lxc/cgroup.c b/src/lxc/cgroup.c
> index 23c8c96..63a2ad4 100644
> --- a/src/lxc/cgroup.c
> +++ b/src/lxc/cgroup.c
> @@ -168,14 +168,6 @@ int lxc_cgroup_get(const char *filename, char *value,
> size_t len, const char *na
> return -1;
> }
>
> -void restart_cgroups(void)
> -{
> - if (ops && ops->disconnect)
> - ops->disconnect();
> - ops = NULL;
> - cgroup_ops_init();
> -}
> -
> void cgroup_disconnect(void)
> {
> if (ops && ops->disconnect)
> diff --git a/src/lxc/cgroup.h b/src/lxc/cgroup.h
> index 8cba030..3e222a8 100644
> --- a/src/lxc/cgroup.h
> +++ b/src/lxc/cgroup.h
> @@ -65,7 +65,6 @@ extern bool cgroup_create_legacy(struct lxc_handler
> *handler);
> extern int cgroup_nrtasks(struct lxc_handler *handler);
> extern const char *cgroup_get_cgroup(struct lxc_handler *handler, const char
> *subsystem);
> extern bool cgroup_unfreeze(struct lxc_handler *handler);
> -extern void restart_cgroups(void);
> extern void cgroup_disconnect(void);
>
> #endif
> diff --git a/src/lxc/lxccontainer.c b/src/lxc/lxccontainer.c
> index b0ae44b..b7adebe 100644
> --- a/src/lxc/lxccontainer.c
> +++ b/src/lxc/lxccontainer.c
> @@ -637,7 +637,6 @@ static bool lxcapi_start(struct lxc_container *c, int
> useinit, char * const argv
> open("/dev/null", O_RDWR);
> open("/dev/null", O_RDWR);
> setsid();
> - restart_cgroups();
> } else {
> if (!am_single_threaded()) {
> ERROR("Cannot start non-daemonized container when
> threaded");
> diff --git a/src/lxc/start.c b/src/lxc/start.c
> index 97c8207..eb1c659 100644
> --- a/src/lxc/start.c
> +++ b/src/lxc/start.c
> @@ -773,6 +773,7 @@ static int lxc_spawn(struct lxc_handler *handler)
> {
> int failed_before_rename = 0;
> const char *name = handler->name;
> + bool cgroups_connected = false;
> int saved_ns_fd[LXC_NS_MAX];
> int preserve_mask = 0, i;
> int netpipepair[2], nveths;
> @@ -842,6 +843,8 @@ static int lxc_spawn(struct lxc_handler *handler)
> goto out_delete_net;
> }
>
> + cgroups_connected = true;
> +
> if (!cgroup_create(handler)) {
> ERROR("failed creating cgroups");
> goto out_delete_net;
> @@ -953,6 +956,7 @@ static int lxc_spawn(struct lxc_handler *handler)
> }
>
> cgroup_disconnect();
> + cgroups_connected = false;
>
> /* Tell the child to complete its initialization and wait for
> * it to exec or return an error. (the child will never
> @@ -981,6 +985,8 @@ static int lxc_spawn(struct lxc_handler *handler)
> return 0;
>
> out_delete_net:
> + if (cgroups_connected)
> + cgroup_disconnect();
> if (handler->clone_flags & CLONE_NEWNET)
> lxc_delete_network(handler);
> out_abort:
> --
> 1.9.0
>
> _______________________________________________
> lxc-devel mailing list
> [email protected]
> http://lists.linuxcontainers.org/listinfo/lxc-devel
--
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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