upon daemonizing, wait on mtab update to terminate in parent

This fixes the race in between the mtab update attempts of mount and umount
when we do a lazy umount right after mounting, in order to hide the given fs
instance; yet this way we still avoid the deadlock of the fs and mount which
we can hit if we wait unconditionally for the mtab update to terminate (cf.
bz #511).

Signed-off-by: Csaba Henk <csaba@gluster.com>
Signed-off-by: Anand Avati <avati@gluster.com>

BUG: 2690 (race between mtab updates of mount and umount)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=2690

5 files changed, 52 insertions, 33 deletions

diff --git a/contrib/apple/daemon.c b/contrib/apple/daemon.c
index 9389201a1af..07dbbc400b3 100644
--- a/contrib/apple/daemon.c
+++ b/contrib/apple/daemon.c
@@ -44,7 +44,7 @@
 #include <unistd.h>
 
 int
-os_daemon(nochdir, noclose)
+os_daemon_return(nochdir, noclose)
 	int nochdir, noclose;
 {
 	struct sigaction osa, sa;
@@ -52,6 +52,7 @@ os_daemon(nochdir, noclose)
 	pid_t newgrp;
 	int oerrno;
 	int osa_ok;
+	int ret;
 
 	/* A SIGHUP may be thrown when the parent exits below. */
 	sigemptyset(&sa.sa_mask);
@@ -59,14 +60,9 @@ os_daemon(nochdir, noclose)
 	sa.sa_flags = 0;
 	osa_ok = sigaction(SIGHUP, &sa, &osa);
 
-	switch (fork()) {
-	case -1:
-		return (-1);
-	case 0:
-		break;
-	default:
-		_exit(0);
-	}
+	ret = fork();
+	if (ret)
+		return ret;
 
 	newgrp = setsid();
 	oerrno = errno;
@@ -90,3 +86,15 @@ os_daemon(nochdir, noclose)
 	}
 	return (0);
 }
+
+int
+os_daemon(int nochdir, int noclose)
+{
+	int ret;
+
+	ret = os_daemon_return(nochdir, noclose);
+	if (ret <= 0)
+		return ret;
+
+	_exit(0);
+}
diff --git a/contrib/apple/daemon.h b/contrib/apple/daemon.h
index 7a2824b6a47..aa88d9baa56 100644
--- a/contrib/apple/daemon.h
+++ b/contrib/apple/daemon.h
@@ -17,4 +17,5 @@
    <http://www.gnu.org/licenses/>.
 */
 
+int os_daemon_return(int nochdir, int noclose);
 int os_daemon(int nochdir, int noclose);
diff --git a/contrib/fuse-include/fuse-mount.h b/contrib/fuse-include/fuse-mount.h
index ca571ce5e30..9f83faf02a0 100644
--- a/contrib/fuse-include/fuse-mount.h
+++ b/contrib/fuse-include/fuse-mount.h
@@ -8,4 +8,5 @@
 */
 
 void gf_fuse_unmount (const char *mountpoint, int fd);
-int gf_fuse_mount (const char *mountpoint, char *fsname, char *mnt_param);
+int gf_fuse_mount (const char *mountpoint, char *fsname, char *mnt_param,
+                   pid_t *mtab_pid);
diff --git a/contrib/fuse-lib/mount.c b/contrib/fuse-lib/mount.c
index 47592a62dd8..f922b07d44b 100644
--- a/contrib/fuse-lib/mount.c
+++ b/contrib/fuse-lib/mount.c
@@ -97,7 +97,8 @@ static
 #endif
 int
 fuse_mnt_add_mount (const char *progname, const char *fsname,
-                    const char *mnt, const char *type, const char *opts)
+                    const char *mnt, const char *type, const char *opts,
+                    pid_t *mtab_pid)
 {
         int res;
         int status;
@@ -125,19 +126,22 @@ fuse_mnt_add_mount (const char *progname, const char *fsname,
                 char templ[] = "/tmp/fusermountXXXXXX";
                 char *tmp;
 
-                /* mtab update done async, just log if fails */
-                res = fork ();
-                if (res)
-                        exit (res == -1 ? 1 : 0);
-                res = fork ();
-                if (res) {
-                        if (res != -1)
-                                res = waitpid (res, &status, 0);
-                        if (res == -1)
-                                GFFUSE_LOGERR ("%s: /etc/mtab update failed",
-                                               progname);
-
-                        exit (0);
+                if (!mtab_pid) {
+                        /* mtab update done async, just log if fails */
+                        res = fork ();
+                        if (res)
+                                exit (res == -1 ? 1 : 0);
+                        res = fork ();
+                        if (res) {
+                                if (res != -1) {
+                                        if (!(res == waitpid (res, &status, 0)
+                                              && status == 0))
+                                                GFFUSE_LOGERR ("%s: /etc/mtab "
+                                                               "update failed",
+                                                               progname);
+                                }
+                                exit (0);
+                        }
                 }
 
                 sigprocmask (SIG_SETMASK, &oldmask, NULL);
@@ -165,13 +169,16 @@ fuse_mnt_add_mount (const char *progname, const char *fsname,
                                progname, strerror (errno));
                 exit (1);
         }
-        res = waitpid (res, &status, 0);
+        if (mtab_pid) {
+                *mtab_pid = res;
+                res = 0;
+        } else {
+                if (!(res == waitpid (res, &status, 0) && status == 0))
+                        res = -1;
+        }
         if (res == -1)
                 GFFUSE_LOGERR ("%s: waitpid: %s", progname, strerror (errno));
 
-        if (status != 0)
-                res = -1;
-
  out_restore:
         sigprocmask (SIG_SETMASK, &oldmask, NULL);
         return res;
@@ -519,7 +526,7 @@ gf_fuse_unmount (const char *mountpoint, int fd)
 
 #ifndef FUSE_UTIL
 static int
-fuse_mount_sys (const char *mountpoint, char *fsname, char *mnt_param)
+fuse_mount_sys (const char *mountpoint, char *fsname, char *mnt_param, pid_t *mtab_pid)
 {
         int fd = -1, ret = -1;
         unsigned mounted = 0;
@@ -573,7 +580,7 @@ fuse_mount_sys (const char *mountpoint, char *fsname, char *mnt_param)
                 }
 
                 ret = fuse_mnt_add_mount ("fuse", source, newmnt, fstype,
-                                          mnt_param);
+                                          mnt_param, mtab_pid);
                 FREE (newmnt);
                 if (ret == -1) {
                         GFFUSE_LOGERR ("failed to add mtab entry");
@@ -625,13 +632,14 @@ escape (char *s)
 }
 
 int
-gf_fuse_mount (const char *mountpoint, char *fsname, char *mnt_param)
+gf_fuse_mount (const char *mountpoint, char *fsname, char *mnt_param,
+               pid_t *mtab_pid)
 {
         int fd = -1, rv = -1;
         char *fm_mnt_params = NULL, *p = NULL;
         char *efsname = NULL;
 
-        fd = fuse_mount_sys (mountpoint, fsname, mnt_param);
+        fd = fuse_mount_sys (mountpoint, fsname, mnt_param, mtab_pid);
         if (fd == -1) {
                 gf_log ("glusterfs-fuse", GF_LOG_INFO,
                         "direct mount failed (%s), "
diff --git a/contrib/macfuse/mount_darwin.c b/contrib/macfuse/mount_darwin.c
index 9d87fca3596..c485583e96b 100644
--- a/contrib/macfuse/mount_darwin.c
+++ b/contrib/macfuse/mount_darwin.c
@@ -133,7 +133,8 @@ Return:
 }
 
 int
-gf_fuse_mount (const char *mountpoint, char *fsname, char *mnt_param)
+gf_fuse_mount (const char *mountpoint, char *fsname, char *mnt_param,
+               pid_t *mtab_pid /* not used on OS X */)
 {
     int fd, pid;
     int result;