perf callchain: Reference count maps

If dso__load_kcore frees all of the existing maps, but one has already
been attached to a callchain cursor node, then we can get a SIGSEGV in
any function that happens to try to use this invalid cursor.  Use the
existing map refcount mechanism to forestall cleanup of a map until the
cursor iterates past the node.

Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: stable@kernel.org
Fixes: 84c2cafa2889 ("perf tools: Reference count struct map")
Link: http://lkml.kernel.org/r/20170106062331.GB2707@templeofstupid.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

3 files changed, 22 insertions, 2 deletions

diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
index 42922512c1c6..8b610dd9e2f6 100644
--- a/tools/perf/util/callchain.c
+++ b/tools/perf/util/callchain.c
@@ -437,7 +437,7 @@ fill_node(struct callchain_node *node, struct callchain_cursor *cursor)
                 }
                 call->ip = cursor_node->ip;
                 call->ms.sym = cursor_node->sym;
-                call->ms.map = cursor_node->map;
+                call->ms.map = map__get(cursor_node->map);
 
                 if (cursor_node->branch) {
                         call->branch_count = 1;
@@ -477,6 +477,7 @@ add_child(struct callchain_node *parent,
 
                 list_for_each_entry_safe(call, tmp, &new->val, list) {
                         list_del(&call->list);
+                        map__zput(call->ms.map);
                         free(call);
                 }
                 free(new);
@@ -761,6 +762,7 @@ merge_chain_branch(struct callchain_cursor *cursor,
                                         list->ms.map, list->ms.sym,
                                         false, NULL, 0, 0);
                 list_del(&list->list);
+                map__zput(list->ms.map);
                 free(list);
         }
 
@@ -811,7 +813,8 @@ int callchain_cursor_append(struct callchain_cursor *cursor,
         }
 
         node->ip = ip;
-        node->map = map;
+        map__zput(node->map);
+        node->map = map__get(map);
         node->sym = sym;
         node->branch = branch;
         node->nr_loop_iter = nr_loop_iter;
@@ -1142,11 +1145,13 @@ static void free_callchain_node(struct callchain_node *node)
 
         list_for_each_entry_safe(list, tmp, &node->parent_val, list) {
                 list_del(&list->list);
+                map__zput(list->ms.map);
                 free(list);
         }
 
         list_for_each_entry_safe(list, tmp, &node->val, list) {
                 list_del(&list->list);
+                map__zput(list->ms.map);
                 free(list);
         }
 
@@ -1210,6 +1215,7 @@ int callchain_node__make_parent_list(struct callchain_node *node)
                                 goto out;
                         *new = *chain;
                         new->has_children = false;
+                        map__get(new->ms.map);
                         list_add_tail(&new->list, &head);
                 }
                 parent = parent->parent;
@@ -1230,6 +1236,7 @@ int callchain_node__make_parent_list(struct callchain_node *node)
 out:
         list_for_each_entry_safe(chain, new, &head, list) {
                 list_del(&chain->list);
+                map__zput(chain->ms.map);
                 free(chain);
         }
         return -ENOMEM;
diff --git a/tools/perf/util/callchain.h b/tools/perf/util/callchain.h
index 35c8e379530f..4f4b60f1558a 100644
--- a/tools/perf/util/callchain.h
+++ b/tools/perf/util/callchain.h
@@ -5,6 +5,7 @@
 #include <linux/list.h>
 #include <linux/rbtree.h>
 #include "event.h"
+#include "map.h"
 #include "symbol.h"
 
 #define HELP_PAD "\t\t\t\t"
@@ -184,8 +185,13 @@ int callchain_merge(struct callchain_cursor *cursor,
  */
 static inline void callchain_cursor_reset(struct callchain_cursor *cursor)
 {
+        struct callchain_cursor_node *node;
+
         cursor->nr = 0;
         cursor->last = &cursor->first;
+
+        for (node = cursor->first; node != NULL; node = node->next)
+                map__zput(node->map);
 }
 
 int callchain_cursor_append(struct callchain_cursor *cursor, u64 ip,
diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index 6770a9645609..7d1b7d33e644 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -1,6 +1,7 @@
 #include "util.h"
 #include "build-id.h"
 #include "hist.h"
+#include "map.h"
 #include "session.h"
 #include "sort.h"
 #include "evlist.h"
@@ -1019,6 +1020,10 @@ int hist_entry_iter__add(struct hist_entry_iter *iter, struct addr_location *al,
                          int max_stack_depth, void *arg)
 {
         int err, err2;
+        struct map *alm = NULL;
+
+        if (al && al->map)
+                alm = map__get(al->map);
 
         err = sample__resolve_callchain(iter->sample, &callchain_cursor, &iter->parent,
                                         iter->evsel, al, max_stack_depth);
@@ -1058,6 +1063,8 @@ out:
         if (!err)
                 err = err2;
 
+        map__put(alm);
+
         return err;
 }