[LTP] [PATCH v2] lib: shell: Fix timeout process races
Cyril Hrubis
chrubis@suse.cz
Mon Sep 20 14:21:46 CEST 2021
There were actually several races in the shell library timeout handling.
This commit fixes hopefully all of them by:
* Reimplementing the backgroud timer in C
* Making sure that the timer has started before we leave test setup
The rewrite of the backround timer to C allows us to run all the timeout
logic in a single process, which simplifies the whole problem greatly
since previously we had chain of processes that estabilished signal
handlers to kill it's descendants, which in the end had a few races in
it.
The race that caused the problems is, as far as I can tell, in the way
how shell spawns it's children. I haven't checked the shell code, but I
guess that when shell runs a process in bacground it does vfork()
+ exec() and because signals are ignored during the operation. My guess
that signals are disabled between vfork() and exec(). If the SIGTERM
arrives at that point it gets lost.
That means that we created a race window in the shell library each time
we started a new process. The rewrite to C simplifies the code but we
still end up with a single place where this can happen and that is when
we execute the tst_timeout_kill binary. This is now fixed in the shell
library by waiting until the background process gets to a sleep state.
Reported-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
---
testcases/lib/.gitignore | 1 +
testcases/lib/Makefile | 2 +-
testcases/lib/tst_test.sh | 47 ++++++--------------
testcases/lib/tst_timeout_kill.c | 75 ++++++++++++++++++++++++++++++++
4 files changed, 90 insertions(+), 35 deletions(-)
create mode 100644 testcases/lib/tst_timeout_kill.c
Changes in v2:
- simplify the message printing
- fix .gitignore entry
diff --git a/testcases/lib/.gitignore b/testcases/lib/.gitignore
index 5a0e8cba2..9625d9043 100644
--- a/testcases/lib/.gitignore
+++ b/testcases/lib/.gitignore
@@ -14,3 +14,4 @@
/tst_sleep
/tst_supported_fs
/tst_hexdump
+/tst_timeout_kill
diff --git a/testcases/lib/Makefile b/testcases/lib/Makefile
index 179b47479..d6b4c7a91 100644
--- a/testcases/lib/Makefile
+++ b/testcases/lib/Makefile
@@ -11,6 +11,6 @@ INSTALL_TARGETS := *.sh
MAKE_TARGETS := tst_sleep tst_random tst_checkpoint tst_rod tst_kvcmp\
tst_device tst_net_iface_prefix tst_net_ip_prefix tst_net_vars\
tst_getconf tst_supported_fs tst_check_drivers tst_get_unused_port\
- tst_get_median tst_hexdump tst_get_free_pids
+ tst_get_median tst_hexdump tst_get_free_pids tst_timeout_kill
include $(top_srcdir)/include/mk/generic_leaf_target.mk
diff --git a/testcases/lib/tst_test.sh b/testcases/lib/tst_test.sh
index 8f69b0551..2556b28f5 100644
--- a/testcases/lib/tst_test.sh
+++ b/testcases/lib/tst_test.sh
@@ -474,27 +474,6 @@ _tst_multiply_timeout()
return 0
}
-_tst_kill_test()
-{
- local i=10
-
- trap '' TERM
- tst_res TBROK "Test timed out, sending SIGTERM! If you are running on slow machine, try exporting LTP_TIMEOUT_MUL > 1"
- kill -TERM -$pid
- tst_sleep 100ms
-
- while kill -0 $pid >/dev/null 2>&1 && [ $i -gt 0 ]; do
- tst_res TINFO "Test is still running, waiting ${i}s"
- sleep 1
- i=$((i-1))
- done
-
- if kill -0 $pid >/dev/null 2>&1; then
- tst_res TBROK "Test still running, sending SIGKILL"
- kill -KILL -$pid
- fi
-}
-
_tst_cleanup_timer()
{
if [ -n "$_tst_setup_timer_pid" ]; then
@@ -503,18 +482,6 @@ _tst_cleanup_timer()
fi
}
-_tst_timeout_process()
-{
- local sleep_pid
-
- sleep $sec &
- sleep_pid=$!
- trap "kill $sleep_pid; exit" TERM
- wait $sleep_pid
- trap - TERM
- _tst_kill_test
-}
-
_tst_setup_timer()
{
TST_TIMEOUT=${TST_TIMEOUT:-300}
@@ -539,9 +506,21 @@ _tst_setup_timer()
_tst_cleanup_timer
- _tst_timeout_process &
+ tst_timeout_kill $sec $pid &
_tst_setup_timer_pid=$!
+
+ while true; do
+ local state
+
+ state=$(cut -d' ' -f3 "/proc/$_tst_setup_timer_pid/stat")
+
+ if [ "$state" = "S" ]; then
+ break;
+ fi
+
+ tst_sleep 1ms
+ done
}
tst_require_root()
diff --git a/testcases/lib/tst_timeout_kill.c b/testcases/lib/tst_timeout_kill.c
new file mode 100644
index 000000000..d55367d31
--- /dev/null
+++ b/testcases/lib/tst_timeout_kill.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2021 Cyril Hrubis <chrubis@suse.cz>
+ */
+
+#include <stdio.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+
+static void print_help(const char *name)
+{
+ fprintf(stderr, "usage: %s timeout pid\n", name);
+}
+
+#define print_msg(fmt, ...) fprintf(stderr, fmt "\n", ##__VA_ARGS__)
+
+int main(int argc, char *argv[])
+{
+ int timeout, pid, ret, i;
+
+ if (argc != 3) {
+ print_help(argv[0]);
+ return 1;
+ }
+
+ timeout = atoi(argv[1]);
+ pid = atoi(argv[2]);
+
+ if (timeout < 0) {
+ fprintf(stderr, "Invalid timeout '%s'\n", argv[1]);
+ print_help(argv[0]);
+ return 1;
+ }
+
+ if (pid <= 1) {
+ fprintf(stderr, "Invalid pid '%s'\n", argv[2]);
+ print_help(argv[0]);
+ return 1;
+ }
+
+ if (timeout)
+ sleep(timeout);
+
+ print_msg("Test timed out, sending SIGTERM!");
+ print_msg("If you are running on slow machine, try exporting LTP_TIMEOUT_MUL > 1");
+
+ ret = kill(-pid, SIGTERM);
+ if (ret) {
+ print_msg("kill(%i) failed: %s", -pid, strerror(errno));
+ return 1;
+ }
+
+ usleep(100000);
+
+ i = 10;
+
+ while (!kill(-pid, 0) && i-- > 0) {
+ print_msg("Test is still running...");
+ sleep(1);
+ }
+
+ if (!kill(-pid, 0)) {
+ print_msg("Test is still running, sending SIGKILL");
+ ret = kill(-pid, SIGKILL);
+ if (ret) {
+ print_msg("kill(%i) failed: %s", -pid, strerror(errno));
+ return 1;
+ }
+ }
+
+ return 0;
+}
--
2.32.0
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