We sometimes erroneously detected processes in other sessions as belonging to our session. Conseque…

build/install-chroot.sh

 #!/bin/bash -e
 
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This script installs Debian-derived distributions in a chroot environment.
 # It can for example be used to have an accurate 32bit build and test
 # environment when otherwise working on a 64bit machine.
 # N. B. it is unlikely that this script will ever work on anything other than a
@@ skipping 479 matching lines @@
   case "$1" in
     --)             shift; break;;
     -h|--help)      shift; help;;
     -l|--list)      shift; list;;
     -c|--clean)     shift; clean "${chroot}";;
     -C|--clean-all) shift; clean;;
     *)              break;;
   esac
 done
 
+# Start a new chroot session and keep track of the session id. We inject this
+# id into all processes that run inside the chroot. Unless they go out of their
+# way to clear their environment, we can then later identify our child and
+# grand-child processes by scanning their environment.
 session="$(schroot -c "${chroot}" -b)"
+export CHROOT_SESSION_ID="${session}"
 
 if [ $# -eq 0 ]; then
+  # Run an interactive shell session
   schroot -c "${session}" -r -p
 else
+  # Run a command inside of the chroot environment
   p="$1"; shift
   schroot -c "${session}" -r -p "$p" -- "$@"
 fi
 rc=$?
 
+# Compute the inode of the root directory inside of the chroot environment.
 i=$(schroot -c "${session}" -r -p ls -- -id /proc/self/root/. |
      awk '{ print $1 }') 2>/dev/null
+other_pids=
 while [ -n "$i" ]; do
-  pids=$(ls -id1 /proc/*/root/. 2>/dev/null |
+  # Identify processes by the inode number of their root directory. Then
+  # remove all processes that we know belong to other sessions. We use
+  # "sort | uniq -u" to do what amounts to a "set substraction operation".
+  pids=$({ ls -id1 /proc/*/root/. 2>/dev/null |
          sed -e 's,^[^0-9]*'$i'.*/\([1-9][0-9]*\)/.*$,\1,
                  t
-                 d') >/dev/null 2>&1
-  [ -z "$pids" ] && break
-  kill -9 $pids
+                 d';
+         echo "${other_pids}";
+         echo "${other_pids}"; } | sort | uniq -u) >/dev/null 2>&1
+  # Kill all processes that are still left running in the session. This is
+  # typically an assortment of daemon processes that were started
+  # automatically. They result in us being unable to tear down the session
+  # cleanly.
+  [ -z "${pids}" ] && break
+  for j in $pids; do
+    # Unfortunately, the way that schroot sets up sessions has the
+    # side-effect of being unable to tell one session apart from another.
+    # This can result in us attempting to kill processes in other sessions.
+    # We make a best-effort to avoid doing so.
+    k="$( ( xargs -0 -n1 </proc/$j/environ ) 2>/dev/null |
+         sed 's/^CHROOT_SESSION_ID=/x/;t1;d;:1;q')"
+    if [ -n "${k}" -a "${k#x}" != "${session}" ]; then
+      other_pids="${other_pids}
+${j}"
+      continue
+    fi
+    kill -9 $pids
+  done
 done
+# End the chroot session. This should clean up all temporary files. But if we
+# earlier failed to terminate all (daemon) processes inside of the session,
+# deleting the session could fail. When that happens, the user has to manually
+# clean up the stale files by invoking us with "--clean" after having killed
+# all running processes.
 schroot -c "${session}" -e
 exit $rc
 EOF
 sudo chown root:root /usr/local/bin/"${target%bit}"
 sudo chmod 755 /usr/local/bin/"${target%bit}"
 
 # Add the standard Ubuntu update repositories if requested.
 [ "${alt_repos}" = "y" -a \
   -r "/var/lib/chroot/${target}/etc/apt/sources.list" ] &&
 sudo sed -i '/^deb .* [^ -]\+ main$/p
@@ skipping 277 matching lines @@
 
 For Chrome, this probably means you want to make your "out" directory a
 symbolic link that points somewhere inside of "${HOME}/chroot".
 
 You still need to run "gclient runhooks" whenever you switch from building
 outside of the chroot to inside of the chroot. But you will find that you
 don't have to repeatedly erase and then completely rebuild all your object
 and binary files.
 
 EOF