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android: Fix background command PID detection

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Close the race between the background command and the detection of its
PID by freezing it while we detect the PID, then resuming it.
This commit is contained in:
Douglas Raillard 2022-04-05 15:44:18 +01:00 committed by Marc Bonnici
parent 14b4e2069b
commit 900531b417
1 changed files with 32 additions and 16 deletions
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48
devlib/utils/android.py
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@ -654,33 +654,49 @@ def adb_background_shell(conn, command,
"""Runs the specified command in a subprocess, returning the the Popen object."""
device = conn.device
adb_server = conn.adb_server
busybox = conn.busybox
_check_env()
stdout, stderr, command = redirect_streams(stdout, stderr, command)
if as_root:
command = 'echo {} | su'.format(quote(command))
command = f'{busybox} printf "%s" {quote(command)} | su'
# Attach a unique UUID to the command line so it can be looked for without
# any ambiguity with ps
uuid_ = uuid.uuid4().hex
uuid_var = 'BACKGROUND_COMMAND_UUID={}'.format(uuid_)
command = "{} sh -c {}".format(uuid_var, quote(command))
def with_uuid(cmd):
# Attach a unique UUID to the command line so it can be looked for
# without any ambiguity with ps
uuid_ = uuid.uuid4().hex
# Unset the var, since not all connection types set it. This will avoid
# anyone depending on that value.
cmd = f'DEVLIB_CMD_UUID={uuid_}; unset DEVLIB_CMD_UUID; {cmd}'
# Ensure we have an sh -c layer so that the UUID will appear on the
# command line parameters of at least one command.
cmd = f'exec {busybox} sh -c {quote(cmd)}'
return (uuid_, cmd)
# Freeze the command with SIGSTOP to avoid racing with PID detection.
command = f"{busybox} kill -STOP $$ && exec {busybox} sh -c {quote(command)}"
command_uuid, command = with_uuid(command)
adb_cmd = get_adb_command(device, 'shell', adb_server)
full_command = '{} {}'.format(adb_cmd, quote(command))
full_command = f'{adb_cmd} {quote(command)}'
logger.debug(full_command)
p = subprocess.Popen(full_command, stdout=stdout, stderr=stderr, stdin=subprocess.PIPE, shell=True)
# Out of band PID lookup, to avoid conflicting needs with stdout redirection
find_pid = '{} ps -A -o pid,args | grep {}'.format(conn.busybox, quote(uuid_var))
ps_out = conn.execute(find_pid)
pids = [
int(line.strip().split(' ', 1)[0])
for line in ps_out.splitlines()
]
# The line we are looking for is the first one, since it was started before
# any look up command
pid = sorted(pids)[0]
grep_cmd = f'{busybox} grep {quote(command_uuid)}'
# Find the PID and release the blocked background command with SIGCONT.
# We get multiple PIDs:
# * One from the grep command itself, but we remove it with another grep command.
# * One for each sh -c layer in the command itself.
#
# For each of the parent layer, we issue SIGCONT as it is harmless and
# avoids having to rely on PID ordering (which could be misleading if PIDs
# got recycled).
find_pid = f'''pids=$({busybox} ps -A -o pid,args | {grep_cmd} | {busybox} grep -v {quote(grep_cmd)} | {busybox} awk '{{print $1}}') && {busybox} printf "%s" "$pids" && {busybox} kill -CONT $pids'''
pids = conn.execute(find_pid, as_root=as_root)
# We choose the highest PID as the "control" PID. It actually does not
# really matter which one we pick, as they are all equivalent sh -c layers.
pid = max(map(int, pids.split()))
return (p, pid)
def adb_kill_server(timeout=30, adb_server=None):