[PATCH 4/9] perf sched replay: Realloc the memory of pid_to_task stepwise to adapt to the different pid_max configurations

[Yunlong Song]

Although the memory of pid_to_task can be allocated via calloc according
to the value of /proc/sys/kernel/pid_max, it cannot handle the case when
pid_max is changed after 'perf sched record' has created its perf.data.
If the new pid_max configured in 'perf sched replay' is smaller than the
old pid_max configured in 'perf sched record', then it will cause the
assertion failure problem. To solve this problem, we realloc the memory
of pid_to_task stepwise once the passed-in pid parameter in register_pid
is larger than the current pid_max.

Example:

Test environment: x86_64 with 160 cores

 $ cat /proc/sys/kernel/pid_max
 163840
 $ perf sched record ls
 $ echo 5000 > /proc/sys/kernel/pid_max
 $ cat /proc/sys/kernel/pid_max
 5000

Before this patch:

 $ perf sched replay
 run measurement overhead: 221 nsecs
 sleep measurement overhead: 55356 nsecs
 the run test took 1000011 nsecs
 the sleep test took 1060940 nsecs
 perf: builtin-sched.c:337: register_pid: Assertion `!(pid >= (unsigned
 long)pid_max)' failed.
 Aborted

After this patch:

 $ perf sched replay
 run measurement overhead: 221 nsecs
 sleep measurement overhead: 55611 nsecs
 the run test took 1000026 nsecs
 the sleep test took 1060486 nsecs
 nr_run_events:        10
 nr_sleep_events:      1562
 nr_wakeup_events:     5
 task      0 (                  :1:         1), nr_events: 1
 task      1 (                  :2:         2), nr_events: 1
 task      2 (                  :3:         3), nr_events: 1
 task      3 (                  :5:         5), nr_events: 1
 ...

Signed-off-by: Yunlong Song <yunlong.song@xxxxxxxxxx>
---
 tools/perf/builtin-sched.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 20d887b..dd71481 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -334,7 +334,12 @@ static struct task_desc *register_pid(struct perf_sched *sched,
 			pid_max = MAX_PID;
 		BUG_ON((sched->pid_to_task = calloc(pid_max, sizeof(struct task_desc *))) == NULL);
 	}
-	BUG_ON(pid >= (unsigned long)pid_max);
+	if (pid >= (unsigned long)pid_max) {
+		BUG_ON((sched->pid_to_task = realloc(sched->pid_to_task, (pid + 1) *
+			sizeof(struct task_desc *))) == NULL);
+		while (pid >= (unsigned long)pid_max)
+			sched->pid_to_task[pid_max++] = NULL;
+	}
 
 	task = sched->pid_to_task[pid];
 
-- 
1.8.5.2

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