Merge tag 'irq-api-2022-02-21' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into i2c/for-mergewindow

Provide a tag for maintainers to pull the generic_handle_irq_safe() API.

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);