linux-kernel - [PATCH tip/perf/core 5/7] perf top: support lookup of symbols in other mount namespaces.

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Date:   Fri, 30 Jun 2017 19:18:57 -0700
From:   Krister Johansen <kjlx@...pleofstupid.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Krister Johansen <kjlx@...pleofstupid.com>
Subject: [PATCH tip/perf/core 5/7] 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/builtin-top.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 2bcfa46..c918fef 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