Re: [PATCH v2] test: Wait for output to flush out in enable_pid

Kris Van Hees
2025-07-30T14:18:26Z

I still see intermittent FAILs. I wonder whether there is a potentially unsafe
contruct at work (see below).

On Sat, Jun 28, 2025 at 06:30:50PM -0400, eugene.loh@oracle.com wrote:
> From: Eugene Loh <eugene.loh@oracle.com>
>
> Our luck with this test has been quite good, but it sometimes fails
> to show its last lines of output. That is, we send a USR1 to the
> trigger processes to set off the final output and we immediately
> cat the output files. If there is any delay in handling the signal,
> the last output will be missing.
>
> Have the processes terminate themselves when their last output is
> flushed; then wait for those processes. Also, skip testing altogether if
> there is only a single processor to run the two, hard-spinning processes.
>
> Signed-off-by: Eugene Loh <eugene.loh@oracle.com>
> ---
> test/unittest/usdt/tst.enable_pid.sh | 17 ++++++++++++-----
> test/unittest/usdt/tst.enable_pid.x | 8 ++++++++
> 2 files changed, 20 insertions(+), 5 deletions(-)
> create mode 100755 test/unittest/usdt/tst.enable_pid.x
>
> diff --git a/test/unittest/usdt/tst.enable_pid.sh b/test/unittest/usdt/tst.enable_pid.sh
> index 7f4f68698..296cfb382 100755
> --- a/test/unittest/usdt/tst.enable_pid.sh
> +++ b/test/unittest/usdt/tst.enable_pid.sh
> @@ -33,6 +33,8 @@ EOF
> cat > main.c <<EOF
> #include <signal.h>
> #include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> #include "prov.h"
>
> /* We check if the is-enabled probe is or is not enabled (or unknown). */
> @@ -41,7 +43,7 @@ cat > main.c <<EOF
> #define ENABLED_UNK 3
>
> /* Start with the previous probe "unknown". */
> -int prv = ENABLED_UNK;
> +int prv = ENABLED_UNK, nepochs_left = 4;
> long long num = 0;
>
> /* Report how many times the previous case was encountered. */
> @@ -71,6 +73,9 @@ static void mark_epoch(int sig) {
> report();
> printf("=== epoch ===\n");
> fflush(stdout);
> + nepochs_left--;
> + if (nepochs_left <= 0)
> + exit(0);

I wonder whether this could still cause some output to get lost. I would
actually move the conditional and exit to the end of the loop in main(),
so that we check nepochs_left and exit when <= 0 outside of the interrupt
handler.

I am running a long sequence of this test to see if that helps/fixes it.

> }
>
> int
> @@ -79,7 +84,7 @@ main(int argc, char **argv)
> struct sigaction act;
>
> /* Set USR1 to mark epochs. */
> - act.sa_flags = 0;
> + memset(&act, 0, sizeof(act));
> act.sa_handler = mark_epoch;
> if (sigaction(SIGUSR1, &act, NULL)) {
> printf("set handler failed\n");
> @@ -172,13 +177,15 @@ for pid in 1 $pid1 $pid2 '*'; do
> kill -USR1 $pid2
> done
>
> +# Wait for the processes.
> +wait $pid1
> +wait $pid2
> +
> +# Dump the output.
> echo done
> echo "========== out 1"; cat out.1
> echo "========== out 2"; cat out.2
>
> echo success
>
> -kill -TERM $pid1
> -kill -TERM $pid2
> -
> exit 0
> diff --git a/test/unittest/usdt/tst.enable_pid.x b/test/unittest/usdt/tst.enable_pid.x
> new file mode 100755
> index 000000000..9506674ee
> --- /dev/null
> +++ b/test/unittest/usdt/tst.enable_pid.x
> @@ -0,0 +1,8 @@
> +#!/bin/sh
> +
> +if [ `grep -c ^processor /proc/cpuinfo` -lt 2 ]; then
> + echo test should have at least two processors
> + exit 2
> +fi
> +
> +exit 0
> --
> 2.43.5
>