perf symbols: Find symbols in different mount namespace

Teach perf how to resolve symbols from binaries that are in a different
mount namespace from the tool.  This allows perf to generate meaningful
stack traces even if the binary resides in a different mount namespace
from the tool.

Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
Tested-by: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1499305693-1599-2-git-send-email-kjlx@templeofstupid.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

8 files changed, 180 insertions, 0 deletions

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 4e7ab611377a..beda40ed63b0 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -1236,6 +1236,7 @@ void dso__delete(struct dso *dso)
         dso_cache__free(dso);
         dso__free_a2l(dso);
         zfree(&dso->symsrc_filename);
+        nsinfo__zput(dso->nsinfo);
         pthread_mutex_destroy(&dso->lock);
         free(dso);
 }
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index bd061ba7b47c..78ec637fc68b 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -10,6 +10,7 @@
 #include <linux/types.h>
 #include <linux/bitops.h>
 #include "map.h"
+#include "namespaces.h"
 #include "build-id.h"
 
 enum dso_binary_type {
@@ -187,6 +188,7 @@ struct dso {
                 void     *priv;
                 u64      db_id;
         };
+        struct nsinfo   *nsinfo;
         refcount_t       refcnt;
         char             name[0];
 };
diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
index 2179b2deb730..5dc60ca5a294 100644
--- a/tools/perf/util/map.c
+++ b/tools/perf/util/map.c
@@ -16,6 +16,7 @@
 #include "machine.h"
 #include <linux/string.h>
 #include "srcline.h"
+#include "namespaces.h"
 #include "unwind.h"
 
 static void __maps__insert(struct maps *maps, struct map *map);
@@ -200,6 +201,7 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
                         if (type != MAP__FUNCTION)
                                 dso__set_loaded(dso, map->type);
                 }
+                dso->nsinfo = nsinfo__get(thread->nsinfo);
                 dso__put(dso);
         }
         return map;
diff --git a/tools/perf/util/namespaces.c b/tools/perf/util/namespaces.c
index 67dcbcc73c7d..bcc6bb19cf10 100644
--- a/tools/perf/util/namespaces.c
+++ b/tools/perf/util/namespaces.c
@@ -9,9 +9,13 @@
 #include "namespaces.h"
 #include "util.h"
 #include "event.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sched.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <unistd.h>
 
 struct namespaces *namespaces__new(struct namespaces_event *event)
 {
@@ -35,3 +39,126 @@ void namespaces__free(struct namespaces *namespaces)
 {
         free(namespaces);
 }
+
+void nsinfo__init(struct nsinfo *nsi)
+{
+        char oldns[PATH_MAX];
+        char *newns = NULL;
+        struct stat old_stat;
+        struct stat new_stat;
+
+        if (snprintf(oldns, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
+                return;
+
+        if (asprintf(&newns, "/proc/%d/ns/mnt", nsi->pid) == -1)
+                return;
+
+        if (stat(oldns, &old_stat) < 0)
+                goto out;
+
+        if (stat(newns, &new_stat) < 0)
+                goto out;
+
+        /* Check if the mount namespaces differ, if so then indicate that we
+         * want to switch as part of looking up dso/map data.
+         */
+        if (old_stat.st_ino != new_stat.st_ino) {
+                nsi->need_setns = true;
+                nsi->mntns_path = newns;
+                newns = NULL;
+        }
+
+out:
+        free(newns);
+}
+
+struct nsinfo *nsinfo__new(pid_t pid)
+{
+        struct nsinfo *nsi = calloc(1, sizeof(*nsi));
+
+        if (nsi != NULL) {
+                nsi->pid = pid;
+                nsi->need_setns = false;
+                nsinfo__init(nsi);
+                refcount_set(&nsi->refcnt, 1);
+        }
+
+        return nsi;
+}
+
+void nsinfo__delete(struct nsinfo *nsi)
+{
+        zfree(&nsi->mntns_path);
+        free(nsi);
+}
+
+struct nsinfo *nsinfo__get(struct nsinfo *nsi)
+{
+        if (nsi)
+                refcount_inc(&nsi->refcnt);
+        return nsi;
+}
+
+void nsinfo__put(struct nsinfo *nsi)
+{
+        if (nsi && refcount_dec_and_test(&nsi->refcnt))
+                nsinfo__delete(nsi);
+}
+
+void nsinfo__mountns_enter(struct nsinfo *nsi, struct nscookie *nc)
+{
+        char curpath[PATH_MAX];
+        int oldns = -1;
+        int newns = -1;
+
+        if (nc == NULL)
+                return;
+
+        nc->oldns = -1;
+        nc->newns = -1;
+
+        if (!nsi || !nsi->need_setns)
+                return;
+
+        if (snprintf(curpath, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
+                return;
+
+        oldns = open(curpath, O_RDONLY);
+        if (oldns < 0)
+                return;
+
+        newns = open(nsi->mntns_path, O_RDONLY);
+        if (newns < 0)
+                goto errout;
+
+        if (setns(newns, CLONE_NEWNS) < 0)
+                goto errout;
+
+        nc->oldns = oldns;
+        nc->newns = newns;
+        return;
+
+errout:
+        if (oldns > -1)
+                close(oldns);
+        if (newns > -1)
+                close(newns);
+}
+
+void nsinfo__mountns_exit(struct nscookie *nc)
+{
+        if (nc == NULL || nc->oldns == -1 || nc->newns == -1)
+                return;
+
+        setns(nc->oldns, CLONE_NEWNS);
+
+        if (nc->oldns > -1) {
+                close(nc->oldns);
+                nc->oldns = -1;
+        }
+
+        if (nc->newns > -1) {
+                close(nc->newns);
+                nc->newns = -1;
+        }
+}
diff --git a/tools/perf/util/namespaces.h b/tools/perf/util/namespaces.h
index 468f1e9a1484..b20f6ead7b2d 100644
--- a/tools/perf/util/namespaces.h
+++ b/tools/perf/util/namespaces.h
@@ -11,6 +11,7 @@
 
 #include "../perf.h"
 #include <linux/list.h>
+#include <linux/refcount.h>
 
 struct namespaces_event;
 
@@ -23,4 +24,36 @@ struct namespaces {
 struct namespaces *namespaces__new(struct namespaces_event *event);
 void namespaces__free(struct namespaces *namespaces);
 
+struct nsinfo {
+        pid_t                   pid;
+        bool                    need_setns;
+        char                    *mntns_path;
+        refcount_t              refcnt;
+};
+
+struct nscookie {
+        int                     oldns;
+        int                     newns;
+};
+
+void nsinfo__init(struct nsinfo *nsi);
+struct nsinfo *nsinfo__new(pid_t pid);
+void nsinfo__delete(struct nsinfo *nsi);
+
+struct nsinfo *nsinfo__get(struct nsinfo *nsi);
+void nsinfo__put(struct nsinfo *nsi);
+
+void nsinfo__mountns_enter(struct nsinfo *nsi, struct nscookie *nc);
+void nsinfo__mountns_exit(struct nscookie *nc);
+
+static inline void __nsinfo__zput(struct nsinfo **nsip)
+{
+        if (nsip) {
+                nsinfo__put(*nsip);
+                *nsip = NULL;
+        }
+}
+
+#define nsinfo__zput(nsi) __nsinfo__zput(&nsi)
+
 #endif  /* __PERF_NAMESPACES_H */
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index e7a98dbd2aed..60a9eaa372ef 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -18,6 +18,8 @@
 #include "symbol.h"
 #include "strlist.h"
 #include "intlist.h"
+#include "namespaces.h"
+#include "vdso.h"
 #include "header.h"
 #include "path.h"
 #include "sane_ctype.h"
@@ -1436,9 +1438,17 @@ int dso__load(struct dso *dso, struct map *map)
         struct symsrc *syms_ss = NULL, *runtime_ss = NULL;
         bool kmod;
         unsigned char build_id[BUILD_ID_SIZE];
+        struct nscookie nsc;
 
+        nsinfo__mountns_enter(dso->nsinfo, &nsc);
         pthread_mutex_lock(&dso->lock);
 
+        /* The vdso files always live in the host container, so don't go looking
+         * for them in the container's mount namespace.
+         */
+        if (dso__is_vdso(dso))
+                nsinfo__mountns_exit(&nsc);
+
         /* check again under the dso->lock */
         if (dso__loaded(dso, map->type)) {
                 ret = 1;
@@ -1584,6 +1594,7 @@ out_free:
 out:
         dso__set_loaded(dso, map->type);
         pthread_mutex_unlock(&dso->lock);
+        nsinfo__mountns_exit(&nsc);
 
         return ret;
 }
diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
index 378c418ca0c1..aee9a42102ba 100644
--- a/tools/perf/util/thread.c
+++ b/tools/perf/util/thread.c
@@ -59,6 +59,8 @@ struct thread *thread__new(pid_t pid, pid_t tid)
                 list_add(&comm->list, &thread->comm_list);
                 refcount_set(&thread->refcnt, 1);
                 RB_CLEAR_NODE(&thread->rb_node);
+                /* Thread holds first ref to nsdata. */
+                thread->nsinfo = nsinfo__new(pid);
         }
 
         return thread;
@@ -91,6 +93,7 @@ void thread__delete(struct thread *thread)
                 comm__free(comm);
         }
         unwind__finish_access(thread);
+        nsinfo__zput(thread->nsinfo);
 
         free(thread);
 }
diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
index 4eb849e9098f..cb1a5dd5c2b9 100644
--- a/tools/perf/util/thread.h
+++ b/tools/perf/util/thread.h
@@ -34,6 +34,7 @@ struct thread {
 
         void                    *priv;
         struct thread_stack     *ts;
+        struct nsinfo           *nsinfo;
 #ifdef HAVE_LIBUNWIND_SUPPORT
         void                            *addr_space;
         struct unwind_libunwind_ops     *unwind_libunwind_ops;