[CRIU] [PATCH] cgroup: open cgroup mount point

[Andrew Vagin]

Otherwise it can disappear in any moment.

For example the test system executes tests concurrently and sometimes one
test looks up a mount point, which has been mounted by another test.

==================================== ERROR ====================================
Test: zdtm/live/static/inotify00, Namespace: 1
Dump log   : /var/lib/jenkins/jobs/CRIU-dump/workspace/test/dump/inotify00/15535/1/dump.log
--------------------------------- grep Error ---------------------------------
(00.021951) Error (cgroup.c:409): cg: failed walking /var/lib/jenkins/jobs/CRIU-dump/workspace/test/dump/signalfd00/15538/1/.criu.cgmounts.UGj28v/ for empty cgroups
(00.021967) Error (cr-dump.c:1601): Dump core (pid: 15535) failed with -1
(00.025509) Error (cr-dump.c:1914): Dumping FAILED.
------------------------------------- END -------------------------------------
================================= ERROR OVER =================================

Reported-by: Jenkins Criuovich
Cc: Tycho Andersen <tycho.andersen at canonical.com>
Signed-off-by: Andrew Vagin <avagin at openvz.org>
---
 cgroup.c | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/cgroup.c b/cgroup.c
index 5114935..16abb64 100644
--- a/cgroup.c
+++ b/cgroup.c
@@ -14,6 +14,7 @@
 #include "proc_parse.h"
 #include "util.h"
 #include "fdset.h"
+#include "util-pie.h"
 #include "protobuf.h"
 #include "protobuf/core.pb-c.h"
 #include "protobuf/cgroup.pb-c.h"
@@ -168,10 +169,11 @@ int parse_cg_info(void)
 	return 0;
 }
 
-static int get_cgroup_mount_point(const char *controller, char *path)
+static int open_cgroup_mount_point(const char *controller)
 {
 	struct mount_info *m;
 	char name[1024];
+	int fd;
 
 	for (m = cg_mntinfo; m != NULL; m = m->next) {
 		if (strcmp(m->fstype->name, "cgroup") == 0) {
@@ -199,8 +201,14 @@ static int get_cgroup_mount_point(const char *controller, char *path)
 
 			if (strcmp(name, controller) == 0) {
 				/* skip the leading '.' in mountpoint */
-				strcpy(path, m->mountpoint + 1);
-				return 0;
+
+				fd = open(m->mountpoint + 1, O_DIRECTORY);
+				if (fd < 0) {
+					pr_perror("Unable to open %s", m->mountpoint + 1);
+					continue;
+				}
+
+				return fd;
 			}
 		}
 	}
@@ -346,11 +354,11 @@ static int collect_cgroups(struct list_head *ctls)
 {
 	struct cg_ctl *cc;
 	int ret = 0;
+	int fd = -1;
 
 	list_for_each_entry(cc, ctls, l) {
 		char path[PATH_MAX];
-		char *name, mount_point[PATH_MAX], prefix[] = ".criu.cgmounts.XXXXXX";
-		bool temp_mount = false;
+		char *name, prefix[] = ".criu.cgmounts.XXXXXX";
 		struct cg_controller *cg;
 
 		if (strstartswith(cc->name, "name="))
@@ -358,13 +366,13 @@ static int collect_cgroups(struct list_head *ctls)
 		else
 			name = cc->name;
 
-		if (get_cgroup_mount_point(name, mount_point) < 0) {
+		fd = open_cgroup_mount_point(name);
+		if (fd < 0) {
 			/* Someone is trying to dump a process that is in
 			 * a controller that isn't mounted, so we mount it for
 			 * them.
 			 */
 			char opts[1024];
-			temp_mount = true;
 
 			if (mkdtemp(prefix) == NULL) {
 				pr_perror("can't make dir for cg mounts\n");
@@ -382,10 +390,12 @@ static int collect_cgroups(struct list_head *ctls)
 				return -1;
 			}
 
-			strcpy(mount_point, prefix);
+			fd = open_detach_mount(prefix);
+			if (fd < 0)
+				return -1;
 		}
 
-		snprintf(path, PATH_MAX, "%s/%s", mount_point, cc->path);
+		snprintf(path, PATH_MAX, "/proc/self/fd/%d/%s", fd, cc->path);
 
 		current_controller = NULL;
 
@@ -420,10 +430,7 @@ static int collect_cgroups(struct list_head *ctls)
 		}
 
 out:
-		if (temp_mount) {
-			umount(prefix);
-			rmdir(prefix);
-		}
+		close_safe(&fd);
 
 		if (ret < 0)
 			return ret;
-- 
1.9.3