linux-kernel - [PATCH v2 tip/perf/core 5/6] perf top: support lookup of symbols in other mount namespaces.

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Date:   Wed,  5 Jul 2017 18:48:12 -0700
From:   Krister Johansen <kjlx@...pleofstupid.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Brendan Gregg <brendan.d.gregg@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Thomas-Mich Richter <tmricht@...ux.vnet.ibm.com>,
        Krister Johansen <kjlx@...pleofstupid.com>
Subject: [PATCH v2 tip/perf/core 5/6] 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@...pleofstupid.com>
---
 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 6052376..ef2aef4 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -586,6 +586,13 @@ 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.
+	 */
+	(void) unshare(CLONE_FS);
+
 	perf_top__sort_new_samples(top);
 
 	/*
@@ -627,6 +634,13 @@ 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.
+	 */
+	(void) unshare(CLONE_FS);
+
 	display_setup_sig();
 	pthread__unblock_sigwinch();
 repeat:
@@ -1205,6 +1219,7 @@ 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[] = {
-- 
2.7.4