geo-rep: Fix sync hang with tarssh

Problem:
Geo-rep sync hangs when tarssh is used as sync
engine at heavy workload.

Analysis and Root cause:
It's found out that the tar process was hung.
When debugged further, it's found out that stderr
buffer of tar process on master was full i.e., 64k.
When the buffer was copied to a file from /proc/pid/fd/2,
the hang is resolved.

This can happen when files picked by tar process
to sync doesn't exist on master anymore. If this count
increases around 1k, the stderr buffer is filled up.

Fix:
The tar process is executed using Popen with stderr as PIPE.
The final execution is something like below.

tar | ssh <args> root@slave tar --overwrite -xf - -C <path>

It was waiting on ssh process first using communicate() and then tar.
Note that communicate() reads stdout and stderr. So when stderr of tar
process is filled up, there is no one to read until untar via ssh is
completed. This can't happen and leads to deadlock.
Hence we should be waiting on both process parallely, so that stderr is
read on both processes.

Backport of:
 > Patch: https://review.gluster.org/22684/
 > Change-Id: I609c7cc5c07e210c504771115b4d551a2e891adf
 > BUG: 1707728
 > Signed-off-by: Kotresh HR <khiremat@redhat.com>

Change-Id: I609c7cc5c07e210c504771115b4d551a2e891adf
fixes: bz#1709738
Signed-off-by: Kotresh HR <khiremat@redhat.com>

3 files changed, 163 insertions, 4 deletions

diff --git a/geo-replication/syncdaemon/resource.py b/geo-replication/syncdaemon/resource.py
index 522279bb7e1..b16db607967 100644
--- a/geo-replication/syncdaemon/resource.py
+++ b/geo-replication/syncdaemon/resource.py
@@ -1540,15 +1540,29 @@ class SSH(object):
 
         p0.stdin.close()
         p0.stdout.close()  # Allow p0 to receive a SIGPIPE if p1 exits.
-        # wait for tar to terminate, collecting any errors, further
-        # waiting for transfer to complete
-        _, stderr1 = p1.communicate()
 
         # stdin and stdout of p0 is already closed, Reset to None and
         # wait for child process to complete
         p0.stdin = None
         p0.stdout = None
-        p0.communicate()
+
+        def wait_for_tar(p0):
+            _, stderr = p0.communicate()
+            if log_err:
+                for errline in stderr.strip().split("\n")[:-1]:
+                    if "No such file or directory" not in errline:
+                        logging.error(lf("SYNC Error",
+                                         sync_engine="Tarssh",
+                                         error=errline))
+
+        t = syncdutils.Thread(target=wait_for_tar, args=(p0, ))
+        # wait for tar to terminate, collecting any errors, further
+        # waiting for transfer to complete
+        t.start()
+
+        # wait for ssh process
+        _, stderr1 = p1.communicate()
+        t.join()
 
         if log_err:
             for errline in stderr1.strip().split("\n")[:-1]:
diff --git a/tests/00-geo-rep/georep-stderr-hang.t b/tests/00-geo-rep/georep-stderr-hang.t
new file mode 100644
index 00000000000..496f0e6577d
--- /dev/null
+++ b/tests/00-geo-rep/georep-stderr-hang.t
@@ -0,0 +1,128 @@
+#!/bin/bash
+
+. $(dirname $0)/../include.rc
+. $(dirname $0)/../volume.rc
+. $(dirname $0)/../geo-rep.rc
+. $(dirname $0)/../env.rc
+
+SCRIPT_TIMEOUT=500
+
+AREQUAL_PATH=$(dirname $0)/../utils
+test "`uname -s`" != "Linux" && {
+    CFLAGS="$CFLAGS -lintl";
+}
+build_tester $AREQUAL_PATH/arequal-checksum.c $CFLAGS
+
+### Basic Tests with Distribute Replicate volumes
+
+##Cleanup and start glusterd
+cleanup;
+TEST glusterd;
+TEST pidof glusterd
+
+
+##Variables
+GEOREP_CLI="$CLI volume geo-replication"
+master=$GMV0
+SH0="127.0.0.1"
+slave=${SH0}::${GSV0}
+num_active=2
+num_passive=2
+master_mnt=$M0
+slave_mnt=$M1
+
+############################################################
+#SETUP VOLUMES AND GEO-REPLICATION
+############################################################
+
+##create_and_start_master_volume
+TEST $CLI volume create $GMV0 $H0:$B0/${GMV0}1;
+TEST $CLI volume start $GMV0
+
+##create_and_start_slave_volume
+TEST $CLI volume create $GSV0 $H0:$B0/${GSV0}1;
+TEST $CLI volume start $GSV0
+TEST $CLI volume set $GSV0 performance.stat-prefetch off
+TEST $CLI volume set $GSV0 performance.quick-read off
+TEST $CLI volume set $GSV0 performance.readdir-ahead off
+TEST $CLI volume set $GSV0 performance.read-ahead off
+
+##Mount master
+TEST glusterfs -s $H0 --volfile-id $GMV0 $M0
+
+##Mount slave
+TEST glusterfs -s $H0 --volfile-id $GSV0 $M1
+
+############################################################
+#BASIC GEO-REPLICATION TESTS
+############################################################
+
+TEST create_georep_session $master $slave
+EXPECT_WITHIN $GEO_REP_TIMEOUT 1 check_status_num_rows "Created"
+
+#Config gluster-command-dir
+TEST $GEOREP_CLI $master $slave config gluster-command-dir ${GLUSTER_CMD_DIR}
+
+#Config gluster-command-dir
+TEST $GEOREP_CLI $master $slave config slave-gluster-command-dir ${GLUSTER_CMD_DIR}
+
+#Set changelog roll-over time to 45 secs
+TEST $CLI volume set $GMV0 changelog.rollover-time 45
+
+#Wait for common secret pem file to be created
+EXPECT_WITHIN $GEO_REP_TIMEOUT  0 check_common_secret_file
+
+#Verify the keys are distributed
+EXPECT_WITHIN $GEO_REP_TIMEOUT  0 check_keys_distributed
+
+#Set sync-jobs to 1
+TEST $GEOREP_CLI $master $slave config sync-jobs 1
+
+#Start_georep
+TEST $GEOREP_CLI $master $slave start
+
+touch $M0
+EXPECT_WITHIN $GEO_REP_TIMEOUT  1 check_status_num_rows "Active"
+EXPECT_WITHIN $GEO_REP_TIMEOUT  1 check_status_num_rows "Changelog Crawl"
+
+#Check History Crawl.
+TEST $GEOREP_CLI $master $slave stop
+TEST create_data_hang "rsync_hang"
+TEST create_data "history_rsync"
+TEST $GEOREP_CLI $master $slave start
+EXPECT_WITHIN $GEO_REP_TIMEOUT  1 check_status_num_rows "Active"
+
+#Verify arequal for whole volume
+EXPECT_WITHIN $GEO_REP_TIMEOUT "x0" arequal_checksum ${master_mnt} ${slave_mnt}
+
+#Stop Geo-rep
+TEST $GEOREP_CLI $master $slave stop
+
+#Config tarssh as sync-engine
+TEST $GEOREP_CLI $master $slave config sync-method tarssh
+
+#Create tarssh hang data
+TEST create_data_hang "tarssh_hang"
+TEST create_data "history_tar"
+
+TEST $GEOREP_CLI $master $slave start
+EXPECT_WITHIN $GEO_REP_TIMEOUT  1 check_status_num_rows "Active"
+
+#Verify arequal for whole volume
+EXPECT_WITHIN $GEO_REP_TIMEOUT "x0" arequal_checksum ${master_mnt} ${slave_mnt}
+
+#Stop Geo-rep
+TEST $GEOREP_CLI $master $slave stop
+
+#Delete Geo-rep
+TEST $GEOREP_CLI $master $slave delete
+
+#Cleanup are-equal binary
+TEST rm $AREQUAL_PATH/arequal-checksum
+
+#Cleanup authorized keys
+sed -i '/^command=.*SSH_ORIGINAL_COMMAND#.*/d' ~/.ssh/authorized_keys
+sed -i '/^command=.*gsyncd.*/d' ~/.ssh/authorized_keys
+
+cleanup;
+#G_TESTDEF_TEST_STATUS_NETBSD7=BAD_TEST,BUG=000000
diff --git a/tests/geo-rep.rc b/tests/geo-rep.rc
index 2035b9fe106..e4f014eb6f8 100644
--- a/tests/geo-rep.rc
+++ b/tests/geo-rep.rc
@@ -101,6 +101,23 @@ function create_data()
     chown 1000:1000 ${master_mnt}/${prefix}_chown_f1_ಸಂತಸ
 }
 
+function create_data_hang()
+{
+    prefix=$1
+    mkdir ${master_mnt}/${prefix}
+    cd ${master_mnt}/${prefix}
+    # ~1k files is required with 1 sync-job and hang happens if
+    # stderr buffer of tar/ssh executed with Popen is full (i.e., 64k).
+    # 64k is hit when ~800 files were  not found while syncing data
+    # from master. So around 1k files is required to hit the condition.
+    for i in {1..1000}
+    do
+        echo "test data" > file$i
+        mv -f file$i file
+    done
+    cd -
+}
+
 function chown_file_ok()
 {
     local file_owner=$(stat --format "%u:%g" "$1")