perf jitdump: Fixup in_pidns member when java agent and 'perf record' are not in the same pidns

When running 'perf record' outside a container and the java agent inside
a container the jit_repipe_code_load() and friends will emit
PERF_RECORD_MMAP2 entries for the jitdump records and will check if we
need to fixup the pid/tid:

nspid = jr->load.pid;
pid = jr_entry_pid(jd, jr);
tid = jr_entry_tid(jd, jr);

The jr_entry_pid() function looks if we're in the same pidns:

static pid_t jr_entry_pid(struct jit_buf_desc *jd, union jr_entry *jr)
{
if (jd->nsi && nsinfo__in_pidns(jd->nsi))
return nsinfo__tgid(jd->nsi);
return jr->load.pid;
}

But since the thread, populated from perf.data records, try to figure
out if in the same pidns by actually trying, on the system where 'perf
inject' is running to open a procfs file (a bug that remains to be
fixed), assuming that if it is not possible that is because that thread
terminated and thus we can't get its namespace info and tolerates
nsinfo__init() failing, noting only that that namespace can't be
entered, so don't even try.

But we can kinda get at least that info (thread->nsinfo->in_pidns) from
the data in the perf.data file, namely the pid and tid in the
PERF_RECORD_MMAP2 for the jit-<PID>.dump file generated from the java
agent, if the PERF_RECORD_MMAP2->pid is the same as what is in the
jitdump file, then we're in the same namespace, otherwise we need to use
the PERF_RECORD_MMAP2->pid.

This all has to be revamped for this jitdump + running perf from
outside, as the meaning of in_pidns is being abused, the initialization
of nsinfo->pid with the value coming from the PERF_RECORD_MMAP2 data is
wrong as it is the pid _outside_ the container since perf was running
there.

The hack in this patch at least produces the expected result in this
scenario by following the assumptions in the current codebase for
finding maps and for generating the PERF_RECORD_MMAP2 for the ELF files
synthesized from the jitdump records in jit_repipe_code_load(), etc.s

Reported-by: Francesco Nigro <[e-mail]>
Reported-by: Ilan Green <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Clark Williams <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Yonatan Goldschmidt <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/jitdump.c

···
  * as captured in the RECORD_MMAP record
  */
 static int
-jit_detect(const char *mmap_name, pid_t pid, struct nsinfo *nsi)
+jit_detect(const char *mmap_name, pid_t pid, struct nsinfo *nsi, bool *in_pidns)
  {
 	char *p;
 	char *end = NULL;
···
 	if (!end)
 		return -1;
 
+	*in_pidns = pid == nsinfo__nstgid(nsi);
 	/*
 	 * pid does not match mmap pid
 	 * pid==0 in system-wide mode (synthesized)
+	 *
+	 * If the pid in the file name is equal to the nstgid, then
+	 * the agent ran inside a container and perf outside the
+	 * container, so record it for further use in jit_inject().
 	 */
-	if (pid && pid2 && pid != nsinfo__nstgid(nsi))
+	if (pid && !(pid2 == pid || *in_pidns))
 		return -1;
 	/*
 	 * validate suffix
···
 	struct nsinfo *nsi;
 	struct evsel *first;
 	struct jit_buf_desc jd;
+	bool in_pidns = false;
 	int ret;
 
 	thread = machine__findnew_thread(machine, pid, tid);
···
 	/*
 	 * first, detect marker mmap (i.e., the jitdump mmap)
 	 */
-	if (jit_detect(filename, pid, nsi)) {
+	if (jit_detect(filename, pid, nsi, &in_pidns)) {
 		nsinfo__put(nsi);
 
 		/*
···
 	jd.output  = output;
 	jd.machine = machine;
 	jd.nsi = nsi;
+
+	if (in_pidns)
+		nsinfo__set_in_pidns(nsi);
 
 	/*
 	 * track sample_type to compute id_all layout