Fix race condition when starting env_syncer in enter_chroot.sh.
Sometimes, two processes might start the env_syncer at the same time.
If this occurs, then the pid file will get overwritten and one of the
processes won't be killed.
I've also fixed the env_syncer to properly daemonize, such that
cbuildbot won't wait on the env_syncer to be killed before exiting.
This requires closing stdin, stderr, and stdout.
BUG=chromium-os:17680
TEST=Reproduce hang, and verify that this fixes the hang. Verify that
multiple chroots can be entered at the same time and that the
env_syncer is killed when the last chroot exits. Verify that
cbuildbot is not kept hanging even if the env_syncer doesn't
exit.
Change-Id: I3cb9fbdf47a406e818e12cf91593b8e3481aa578
Reviewed-on: http://gerrit.chromium.org/gerrit/4232
Reviewed-by: Ryan Cui <rcui@chromium.org>
Tested-by: David James <davidjames@chromium.org>
diff --git a/enter_chroot.sh b/enter_chroot.sh
index 8fa593a..79e2f49 100755
--- a/enter_chroot.sh
+++ b/enter_chroot.sh
@@ -136,6 +136,10 @@
sudo chown ${USER} ${FLAGS_chroot}/${file} 1>&2
done
+ # Drop stdin, stderr, stdout, and chroot lock.
+ # This is needed for properly daemonizing the process.
+ exec 0>&- 1>&- 2>&- 200>&-
+
while true; do
# Sync files
for file in ${sync_files}; do
@@ -186,19 +190,20 @@
# Don't use sudo -v since that has issues on machines w/ no password.
sudo echo "" > /dev/null
- # Syncer proc, but only the first time
- if ! [ -f "${SYNCERPIDFILE}" ] || \
- ! [ -d /proc/$(cat "${SYNCERPIDFILE}") ]; then
- debug "Starting sync process"
- env_sync_proc &
- echo $! > "${SYNCERPIDFILE}"
- disown $!
- fi
-
(
flock 200
echo $$ >> "$LOCKFILE"
+ # If there isn't a syncer daemon started already, start one. This daemon
+ # is killed by the enter_chroot that exits last.
+ if ! [ -f "${SYNCERPIDFILE}" ] || \
+ ! [ -d /proc/$(cat "${SYNCERPIDFILE}") ]; then
+ debug "Starting sync process"
+ env_sync_proc &
+ echo $! > "${SYNCERPIDFILE}"
+ disown $!
+ fi
+
debug "Mounting chroot environment."
ensure_mounted none "-t proc" /proc
ensure_mounted none "-t sysfs" /sys
