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-rw-r--r--tools/perf/util/synthetic-events.c19
1 files changed, 19 insertions, 0 deletions
diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 70f095624a0b..b654de0841f8 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -1784,6 +1784,25 @@ int __machine__synthesize_threads(struct machine *machine, struct perf_tool *too
perf_event__handler_t process, bool needs_mmap,
bool data_mmap, unsigned int nr_threads_synthesize)
{
+ /*
+ * When perf runs in non-root PID namespace, and the namespace's proc FS
+ * is not mounted, nsinfo__is_in_root_namespace() returns false.
+ * In this case, the proc FS is coming for the parent namespace, thus
+ * perf tool will wrongly gather process info from its parent PID
+ * namespace.
+ *
+ * To avoid the confusion that the perf tool runs in a child PID
+ * namespace but it synthesizes thread info from its parent PID
+ * namespace, returns failure with warning.
+ */
+ if (!nsinfo__is_in_root_namespace()) {
+ pr_err("Perf runs in non-root PID namespace but it tries to ");
+ pr_err("gather process info from its parent PID namespace.\n");
+ pr_err("Please mount the proc file system properly, e.g. ");
+ pr_err("add the option '--mount-proc' for unshare command.\n");
+ return -EPERM;
+ }
+
if (target__has_task(target))
return perf_event__synthesize_thread_map(tool, threads, process, machine,
needs_mmap, data_mmap);