perf/core: Fix memory leak triggered by perf --namespace

perf with --namespace key leaks various memory objects including namespaces

  4.14.0+
  pid_namespace          1     12   2568   12    8
  user_namespace         1     39    824   39    8
  net_namespace          1      5   6272    5    8

This happen because perf_fill_ns_link_info() struct patch ns_path:
during initialization ns_path incremented counters on related mnt and dentry,
but without lost path_put nobody decremented them back.
Leaked dentry is name of related namespace,
and its leak does not allow to free unused namespace.

Signed-off-by: Vasily Averin <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Hari Bathini <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: commit e422267 ("perf: Add PERF_RECORD_NAMESPACES to include namespaces related info")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: vaverin

kernel/events/core.c

@@ -6756,6 +6756,7 @@ static void perf_fill_ns_link_info(struct perf_ns_link_info *ns_link_info,
 		ns_inode = ns_path.dentry->d_inode;
 		ns_link_info->dev = new_encode_dev(ns_inode->i_sb->s_dev);
 		ns_link_info->ino = ns_inode->i_ino;
+		path_put(&ns_path);
 	}
 }