[tip:perf/core] perf top: Support lookup of symbols in other mount namespaces.

[tip-bot for Krister Johansen]

Commit-ID:  868a832918f621b7576655c00067f20326ef3931
Gitweb:     http://git.kernel.org/tip/868a832918f621b7576655c00067f20326ef3931
Author:     Krister Johansen <kjlx@xxxxxxxxxxxxxxxxxx>
AuthorDate: Wed, 5 Jul 2017 18:48:12 -0700
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Tue, 25 Jul 2017 22:43:16 -0300

perf top: Support lookup of symbols in other mount namespaces.

The perf top command needs to unshare its fs from the helper threads in
order to successfully setns(2) during its symbol lookup.  It also needs
to impelement a force flag to ignore ownership of perf-<pid>.map files.

Signed-off-by: Krister Johansen <kjlx@xxxxxxxxxxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Brendan Gregg <brendan.d.gregg@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas-Mich Richter <tmricht@xxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1499305693-1599-6-git-send-email-kjlx@xxxxxxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/Documentation/perf-top.txt |  4 ++++
 tools/perf/builtin-top.c              | 15 +++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/tools/perf/Documentation/perf-top.txt b/tools/perf/Documentation/perf-top.txt
index e71d638..d864ea6 100644
--- a/tools/perf/Documentation/perf-top.txt
+++ b/tools/perf/Documentation/perf-top.txt
@@ -237,6 +237,10 @@ Default is to monitor all CPUS.
 --hierarchy::
 	Enable hierarchy output.
 
+--force::
+	Don't do ownership validation.
+
+
 INTERACTIVE PROMPTING KEYS
 --------------------------
 
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index e5a8f24..ee954bd 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -587,6 +587,13 @@ static void *display_thread_tui(void *arg)
 		.refresh	= top->delay_secs,
 	};
 
+	/* In order to read symbols from other namespaces perf to  needs to call
+	 * setns(2).  This isn't permitted if the struct_fs has multiple users.
+	 * unshare(2) the fs so that we may continue to setns into namespaces
+	 * that we're observing.
+	 */
+	unshare(CLONE_FS);
+
 	perf_top__sort_new_samples(top);
 
 	/*
@@ -628,6 +635,13 @@ static void *display_thread(void *arg)
 	struct perf_top *top = arg;
 	int delay_msecs, c;
 
+	/* In order to read symbols from other namespaces perf to  needs to call
+	 * setns(2).  This isn't permitted if the struct_fs has multiple users.
+	 * unshare(2) the fs so that we may continue to setns into namespaces
+	 * that we're observing.
+	 */
+	unshare(CLONE_FS);
+
 	display_setup_sig();
 	pthread__unblock_sigwinch();
 repeat:
@@ -1206,6 +1220,7 @@ int cmd_top(int argc, const char **argv)
 		    "Show raw trace event output (do not use print fmt or plugins)"),
 	OPT_BOOLEAN(0, "hierarchy", &symbol_conf.report_hierarchy,
 		    "Show entries in a hierarchy"),
+	OPT_BOOLEAN(0, "force", &symbol_conf.force, "don't complain, do it"),
 	OPT_END()
 	};
 	const char * const top_usage[] = {