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

9 files changed, 101 insertions, 48 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;
diff --git a/glusterfsd/src/Makefile.am b/glusterfsd/src/Makefile.am
index 537eda0bbdd..2056ca89806 100644
--- a/glusterfsd/src/Makefile.am
+++ b/glusterfsd/src/Makefile.am
@@ -1,9 +1,6 @@
 sbin_PROGRAMS = glusterfsd
 
-glusterfsd_SOURCES = glusterfsd.c glusterfsd-mgmt.c
-if GF_DARWIN_HOST_OS
-glusterfsd_SOURCES += $(CONTRIBDIR)/apple/daemon.c
-endif
+glusterfsd_SOURCES = glusterfsd.c glusterfsd-mgmt.c $(CONTRIBDIR)/apple/daemon.c
 glusterfsd_LDADD = $(top_builddir)/libglusterfs/src/libglusterfs.la \
 	$(top_builddir)/rpc/rpc-lib/src/libgfrpc.la \
 	$(top_builddir)/rpc/xdr/src/libgfxdr.la \
@@ -14,10 +11,7 @@ noinst_HEADERS = glusterfsd.h glusterfsd-mem-types.h
 AM_CFLAGS = -fPIC -Wall -D_FILE_OFFSET_BITS=64 -D_GNU_SOURCE -D$(GF_HOST_OS)\
 	-I$(top_srcdir)/libglusterfs/src -DDATADIR=\"$(localstatedir)\" \
 	-DCONFDIR=\"$(sysconfdir)/glusterfs\" $(GF_GLUSTERFS_CFLAGS) \
-	-I$(top_srcdir)/rpc/rpc-lib/src -I$(top_srcdir)/rpc/xdr/src
-if GF_DARWIN_HOST_OS
-AM_CFLAGS += -I$(CONTRIBDIR)/apple
-endif
+	-I$(top_srcdir)/rpc/rpc-lib/src -I$(top_srcdir)/rpc/xdr/src -I$(CONTRIBDIR)/apple
 
 CLEANFILES = 
 
diff --git a/glusterfsd/src/glusterfsd.c b/glusterfsd/src/glusterfsd.c
index 9406d74ac63..2d2024409ee 100644
--- a/glusterfsd/src/glusterfsd.c
+++ b/glusterfsd/src/glusterfsd.c
@@ -25,6 +25,7 @@
 #include <sys/types.h>
 #include <sys/resource.h>
 #include <sys/file.h>
+#include <sys/wait.h>
 #include <netdb.h>
 #include <signal.h>
 #include <libgen.h>
@@ -75,11 +76,7 @@
 #include <fnmatch.h>
 #include "rpc-clnt.h"
 
-#ifdef GF_DARWIN_HOST_OS
 #include "daemon.h"
-#else
-#define os_daemon(u, v) daemon (u, v)
-#endif
 
 
 /* using argp for command line parsing */
@@ -315,6 +312,16 @@ create_fuse_mount (glusterfs_ctx_t *ctx)
                 break;
         }
 
+        if (!cmd_args->no_daemon_mode) {
+                 ret = dict_set_static_ptr (master->options, "sync-mtab",
+                                            "enable");
+                if (ret < 0) {
+                        gf_log ("glusterfsd", GF_LOG_ERROR,
+                                "failed to set dict value for key sync-mtab");
+                        goto err;
+                }
+        }
+
         ret = xlator_init (master);
         if (ret) {
                 gf_log ("", GF_LOG_DEBUG, "failed to initialize fuse translator");
@@ -1310,6 +1317,7 @@ daemonize (glusterfs_ctx_t *ctx)
 {
         int            ret = -1;
         cmd_args_t    *cmd_args = NULL;
+        int            cstatus = 0;
 
         cmd_args = &ctx->cmd_args;
 
@@ -1323,11 +1331,24 @@ daemonize (glusterfs_ctx_t *ctx)
         if (cmd_args->debug_mode)
                 goto postfork;
 
-        ret = os_daemon (0, 0);
-        if (ret == -1) {
+        ret = os_daemon_return (0, 0);
+        switch (ret) {
+        case -1:
                 gf_log ("daemonize", GF_LOG_ERROR,
                         "Daemonization failed: %s", strerror(errno));
                 goto out;
+        case 0:
+                break;
+        default:
+                if (ctx->mtab_pid > 0) {
+                        ret = waitpid (ctx->mtab_pid, &cstatus, 0);
+                        if (!(ret == ctx->mtab_pid && cstatus == 0)) {
+                                gf_log ("daemonize", GF_LOG_ERROR,
+                                        "/etc/mtab update failed");
+                                exit (1);
+                        }
+                }
+                _exit (0);
         }
 
 postfork:
diff --git a/libglusterfs/src/glusterfs.h b/libglusterfs/src/glusterfs.h
index 56b5e2b9c30..5553009b194 100644
--- a/libglusterfs/src/glusterfs.h
+++ b/libglusterfs/src/glusterfs.h
@@ -340,6 +340,7 @@ struct _glusterfs_ctx {
         int                 graph_id; /* Incremented per graph, value should
                                          indicate how many times the graph has
                                          got changed */
+        pid_t               mtab_pid; /* pid of the process which updates the mtab */
 };
 typedef struct _glusterfs_ctx glusterfs_ctx_t;
 
diff --git a/xlators/mount/fuse/src/fuse-bridge.c b/xlators/mount/fuse/src/fuse-bridge.c
index d34a747f4bb..dafc0a93cd3 100644
--- a/xlators/mount/fuse/src/fuse-bridge.c
+++ b/xlators/mount/fuse/src/fuse-bridge.c
@@ -3485,6 +3485,8 @@ init (xlator_t *this_xl)
         int                i = 0;
         int                xl_name_allocated = 0;
         int                fsname_allocated = 0;
+        glusterfs_ctx_t   *ctx = NULL;
+        gf_boolean_t       sync_mtab = _gf_false;
 
         if (this_xl == NULL)
                 return -1;
@@ -3492,6 +3494,10 @@ init (xlator_t *this_xl)
         if (this_xl->options == NULL)
                 return -1;
 
+        ctx = glusterfs_ctx_get ();
+        if (!ctx)
+                return -1;
+
         options = this_xl->options;
 
         if (this_xl->name == NULL) {
@@ -3604,6 +3610,14 @@ init (xlator_t *this_xl)
                 priv->fuse_dump_fd = ret;
         }
 
+        sync_mtab = _gf_false;
+        ret = dict_get_str (options, "sync-mtab", &value_string);
+        if (ret == 0) {
+                ret = gf_string2boolean (value_string,
+                                         &sync_mtab);
+                GF_ASSERT (ret == 0);
+        }
+
         cmd_args = &this_xl->ctx->cmd_args;
         fsname = cmd_args->volfile;
         if (!fsname && cmd_args->volfile_server) {
@@ -3630,7 +3644,8 @@ init (xlator_t *this_xl)
 
         priv->fd = gf_fuse_mount (priv->mount_point, fsname,
                                   "allow_other,default_permissions,"
-                                  "max_read=131072");
+                                  "max_read=131072",
+                                  sync_mtab ? &ctx->mtab_pid : NULL);
         if (priv->fd == -1)
                 goto cleanup_exit;
 
@@ -3727,5 +3742,8 @@ struct volume_options options[] = {
         { .key  = {"client-pid"},
           .type = GF_OPTION_TYPE_INT
         },
+        { .key  = {"sync-mtab"},
+          .type = GF_OPTION_TYPE_BOOL
+        },
         { .key = {NULL} },
 };