[PATCH 09/12] stalld: Add defensive checks in print_boosted_info

[Clark Williams <clrkwllms@kernel.org>]

From: Clark Williams <williams@redhat.com>

This adds validation and bounds checking in print_boosted_info() to
prevent segmentation faults when boosting tasks in FIFO mode.

Changes:
- Add NULL check for 'type' parameter
- Handle fill_process_comm() failures gracefully with fallback
- Validate cpu->id is within valid range before dereferencing
- Provide informative error messages for invalid states

Issue: Test results show stalld crashes with SIGSEGV when using -F
(force FIFO) flag in aggressive mode (-A). The crash occurs during
or immediately after the first boost attempt.

This is a partial fix that adds defensive programming. Further
investigation needed to identify the root cause of the crashes
in FIFO boosting mode.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Clark Williams <clrkwllms@kernel.org>
Signed-off-by: Clark Williams <williams@redhat.com>
---
 src/stalld.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/stalld.c b/src/stalld.c
index ebca23105ce9..466b6db15668 100644
--- a/src/stalld.c
+++ b/src/stalld.c
@@ -435,10 +435,21 @@ void print_boosted_info(int tgid, int pid, struct cpu_info *cpu, char *type)
 {
 	char comm[COMM_SIZE];
 
-	fill_process_comm(tgid, pid, comm, COMM_SIZE);
+	/* Validate inputs to prevent crashes */
+	if (!type) {
+		warn("print_boosted_info called with NULL type\n");
+		return;
+	}
+
+	if (fill_process_comm(tgid, pid, comm, COMM_SIZE) != 0) {
+		/* If we can't get the comm, use a placeholder */
+		snprintf(comm, COMM_SIZE, "<unknown>");
+	}
 
-	if (cpu)
+	if (cpu && cpu->id >= 0 && cpu->id < config_nr_cpus)
 		log_msg("boosted pid %d (%s) (cpu %d) using %s\n", pid, comm, cpu->id, type);
+	else if (cpu)
+		log_msg("boosted pid %d (%s) (cpu <invalid>) using %s\n", pid, comm, type);
 	else
 		log_msg("boosted pid %d (%s) using %s\n", pid, comm, type);
 }
-- 
2.51.0