Re: [PATCH v1 6/8] perf scripts: Add perf-stuck, to tell where a running perf is stuck

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
- [Medium] Time-of-check to time-of-use race condition when accessing process statistics leads to script crash.
- [Medium] Incorrect parsing of /proc/[pid]/stat for processes with spaces in their name.
- [Medium] Unsanitized output of process command lines allows terminal escape sequence injection.
- [Medium] Arithmetic evaluation failure due to awk outputting scientific notation for large CPU times.
--

commit bb6bb44a87ff31de8100a51a6f3b35196458dff1
Author: Arnaldo Carvalho de Melo <acme@redhat.com>

perf scripts: Add perf-stuck, to tell where a running perf is stuck

This commit introduces the perf-stuck.sh script and an accompanying gdb script
to help identify where a running perf process is stuck. It samples /proc/<pid>
at fixed intervals to distinguish between spinning, blocking, and recursion,
and can automatically attach gdb if no progress is made.

> diff --git a/tools/perf/scripts/perf-stuck.sh b/tools/perf/scripts/perf-stuck.sh
> new file mode 100755
> index 0000000000000..8b284bcf5e313
> --- /dev/null
> +++ b/tools/perf/scripts/perf-stuck.sh
> @@ -0,0 +1,165 @@

[ ... ]

> +hz=$(getconf CLK_TCK)
> +psz=$(getconf PAGESIZE)
> +prev_cpu=
> +prev_stack=
> +prev_progress=
> +stuck=0
> +gdb_done=
> +nsample=0
> +
> +echo "watching $pid ($(tr '\0' ' ' < /proc/"$pid"/cmdline)) every ${interval}s"

[Severity: Medium]
Does directly printing the process command line allow for terminal escape
sequence injection?

The tr command does not sanitize non-printable characters, which could allow
a process launched with malicious ANSI escape sequences in its command line
arguments to corrupt the local terminal when monitored.

> +
> +while :; do
> +	if [ ! -d /proc/"$pid" ]; then
> +		echo "$(date +%T) process gone"
> +		break
> +	fi
> +
> +	stat=($(awk '{print $3, $14 + $15, $24}' /proc/"$pid"/stat))

[Severity: Medium]
If the monitored process has a space in its command name (e.g., "(my script)"),
will awk split the name into multiple fields using its default whitespace
delimiter, incorrectly shifting positional variables like $14 and $24?

[Severity: Medium]
If the process terminates immediately after the directory check on the previous
lines, but before the awk command reads the file, will awk return an empty
output?

Because set -u is enabled, accessing the unbound stat[0] variable below
would cause the script to abruptly crash instead of cleanly exiting.

> +	state=${stat[0]}
> +	cpu=${stat[1]}
> +	# field 24 is the resident set size in pages
> +	rss=$(( stat[2] * psz / 1024 ))
> +
> +	stack=$(awk '/\[stack\]/{print $1; exit}' /proc/"$pid"/maps)

[ ... ]

> +	if [ -n "$prev_cpu" ]; then
> +		cpu_delta=$(( cpu - prev_cpu ))

[Severity: Medium]
If the sum of utime and stime ($14 + $15) calculated by awk above exceeds
1,000,000 ticks, will awk format the output in scientific notation (e.g.,
1e+06) based on the default OFMT?

If so, the bash arithmetic context here will be unable to parse this format,
causing a fatal syntax error and crashing the script when monitoring
long-running processes.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260913023459.112654-1-acme@kernel.org?part=6