[PATCH 3/4] perf sched: Fix NULL dereference in latency_runtime_event

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

latency_runtime_event() passes the return value of
machine__findnew_thread() directly to thread_atoms_search() at line
1216, before checking for NULL at line 1220.  thread_atoms_search()
calls pid_cmp() which dereferences the thread pointer via
thread__tid(), causing a NULL pointer dereference if the allocation
fails.

All other callers of thread_atoms_search() in this file
(latency_switch_event, latency_wakeup_event,
latency_migrate_task_event) correctly check for NULL first.

Move the atoms assignment after the NULL check to match the pattern
used by the other callers.

Fixes: b91fc39f4ad7 ("perf machine: Protect the machine->threads with a rwlock")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Assisted-by: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/builtin-sched.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 13b801496a01271e..36da451447b5e59f 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -1213,13 +1213,15 @@ static int latency_runtime_event(struct perf_sched *sched,
 	const u32 pid	   = perf_sample__intval(sample, "pid");
 	const u64 runtime  = perf_sample__intval(sample, "runtime");
 	struct thread *thread = machine__findnew_thread(machine, -1, pid);
-	struct work_atoms *atoms = thread_atoms_search(&sched->atom_root, thread, &sched->cmp_pid);
+	struct work_atoms *atoms;
 	u64 timestamp = sample->time;
 	int cpu = sample->cpu, err = -1;
 
 	if (thread == NULL)
 		return -1;
 
+	atoms = thread_atoms_search(&sched->atom_root, thread, &sched->cmp_pid);
+
 	/* perf.data is untrusted input — CPU may be absent or corrupted */
 	if (cpu >= MAX_CPUS || cpu < 0) {
 		pr_warning("WARNING: at offset %#" PRIx64 ": out-of-bound sample CPU %d, skipping sample\n",
-- 
2.54.0