perf tools: Retry mapping buffers readonly on EACCES

Persistent event buffers may only be mmapped readonly. Thus, retry
mapping it readonly if mmap returns EACCES after trying to mmap
writable.

[ namhyung: Don't write to readonly mmap'ed buffers. ]
Signed-off-by: Robert Richter <robert.richter@linaro.org>
Signed-off-by: Robert Richter <rric@kernel.org>

tools/perf/builtin-record.c

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index a41ac415..f3f7483 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -152,8 +152,8 @@
 	}
 
 	md->prev = old;
-	perf_mmap__write_tail(md, old);
-
+	if (!rec->opts.mmap_ro)
+		perf_mmap__write_tail(md, old);
 out:
 	return rc;
 }
@@ -226,7 +226,12 @@
 		goto out;
 	}
 
-	if (perf_evlist__mmap(evlist, opts->mmap_pages, false) < 0) {
+try_again2:
+	if (perf_evlist__mmap(evlist, opts->mmap_pages, opts->mmap_ro) < 0) {
+		if (!opts->mmap_ro && errno == EACCES) {
+			opts->mmap_ro = true;
+			goto try_again2;
+		}
 		if (errno == EPERM) {
 			pr_err("Permission error mapping pages.\n"
 			       "Consider increasing "

tools/perf/builtin-top.c

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index e37521f..bef7b1d 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -894,8 +894,12 @@
 			goto out_err;
 		}
 	}
-
-	if (perf_evlist__mmap(evlist, opts->mmap_pages, false) < 0) {
+try_again2:
+	if (perf_evlist__mmap(evlist, opts->mmap_pages, opts->mmap_ro) < 0) {
+		if (!opts->mmap_ro && errno == EACCES) {
+			opts->mmap_ro = true;
+			goto try_again2;
+		}
 		ui__error("Failed to mmap with %d (%s)\n",
 			    errno, strerror(errno));
 		goto out_err;

tools/perf/perf.h

diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index cf20187..dca43c72 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -224,6 +224,7 @@
 	bool	     sample_weight;
 	bool	     sample_time;
 	bool	     period;
+	bool	     mmap_ro;
 	unsigned int freq;
 	unsigned int mmap_pages;
 	unsigned int user_freq;