[PATCH 1/2] alloc_tag: add timestamp to codetag iterator

[David Wang <00107082@163.com>]

Codetag iterator use <id,address> pair to guarantee the
validness. But both id and address can be reused, there is
theoretical possibility when module inserted right after
another module removed, kmalloc return an address kfree by
previous module and IDR key reuse the key recently removed.

Add timestamp to codetag_module and code_iterator, the
timestamp is generated by a clock which is strickly
incremented whenever a module is loaded. An iterator is
valid if and only if its timestamp match codetag_module's.

Signed-off-by: David Wang <00107082@163.com>
---
 include/linux/codetag.h |  1 +
 lib/codetag.c           | 12 ++++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/linux/codetag.h b/include/linux/codetag.h
index d14dbd26b370..61d43c3fbd19 100644
--- a/include/linux/codetag.h
+++ b/include/linux/codetag.h
@@ -54,6 +54,7 @@ struct codetag_iterator {
 	struct codetag_module *cmod;
 	unsigned long mod_id;
 	struct codetag *ct;
+	unsigned long timestamp;
 };
 
 #ifdef MODULE
diff --git a/lib/codetag.c b/lib/codetag.c
index 42aadd6c1454..973bfa5dd5db 100644
--- a/lib/codetag.c
+++ b/lib/codetag.c
@@ -13,6 +13,8 @@ struct codetag_type {
 	struct idr mod_idr;
 	struct rw_semaphore mod_lock; /* protects mod_idr */
 	struct codetag_type_desc desc;
+	/* generates timestamp for module load */
+	unsigned long clock;
 };
 
 struct codetag_range {
@@ -23,6 +25,7 @@ struct codetag_range {
 struct codetag_module {
 	struct module *mod;
 	struct codetag_range range;
+	unsigned long timestamp;
 };
 
 static DEFINE_MUTEX(codetag_lock);
@@ -48,6 +51,7 @@ struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype)
 		.cmod = NULL,
 		.mod_id = 0,
 		.ct = NULL,
+		.timestamp = 0,
 	};
 
 	return iter;
@@ -91,11 +95,13 @@ struct codetag *codetag_next_ct(struct codetag_iterator *iter)
 		if (!cmod)
 			break;
 
-		if (cmod != iter->cmod) {
+		if (!iter->cmod || iter->timestamp != cmod->timestamp) {
 			iter->cmod = cmod;
+			iter->timestamp = cmod->timestamp;
 			ct = get_first_module_ct(cmod);
-		} else
+		} else {
 			ct = get_next_module_ct(iter);
+		}
 
 		if (ct)
 			break;
@@ -190,6 +196,8 @@ static int codetag_module_init(struct codetag_type *cttype, struct module *mod)
 	cmod->range = range;
 
 	down_write(&cttype->mod_lock);
+	cttype->clock++;
+	cmod->timestamp = cttype->clock;
 	err = idr_alloc(&cttype->mod_idr, cmod, 0, 0, GFP_KERNEL);
 	if (err >= 0) {
 		cttype->count += range_size(cttype, &range);
-- 
2.39.2