Am 15.10.2015 um 21:02 schrieb David Turner:
On Thu, 2015-10-15 at 05:35 +0200, René Scharfe wrote:
Am 15.10.2015 um 00:07 schrieb David Turner:
From: Keith McGuigan <[email protected]>
During merges, we would previously free entries that we no longer need
in the destination index. But those entries might also be stored in
the dir_entry cache, and when a later call to add_to_index found them,
they would be used after being freed.
To prevent this, add a ref count for struct cache_entry. Whenever
a cache entry is added to a data structure, the ref count is incremented;
when it is removed from the data structure, it is decremented. When
it hits zero, the cache_entry is freed.
Signed-off-by: Keith McGuigan <[email protected]>
Signed-off-by: David Turner <[email protected]>
---
Fix type of ref_count (from unsigned int to int).
cache.h | 27 +++++++++++++++++++++++++++
name-hash.c | 7 ++++++-
read-cache.c | 6 +++++-
split-index.c | 13 ++++++++-----
unpack-trees.c | 6 ++++--
5 files changed, 50 insertions(+), 9 deletions(-)
diff --git a/cache.h b/cache.h
index 752031e..7906026 100644
--- a/cache.h
+++ b/cache.h
@@ -149,6 +149,7 @@ struct stat_data {
struct cache_entry {
struct hashmap_entry ent;
+ int ref_count; /* count the number of refs to this in dir_hash */
struct stat_data ce_stat_data;
unsigned int ce_mode;
unsigned int ce_flags;
@@ -213,6 +214,32 @@ struct cache_entry {
struct pathspec;
/*
+ * Increment the cache_entry reference count. Should be called
+ * whenever a pointer to a cache_entry is retained in a data structure,
+ * thus marking it as alive.
+ */
+static inline void add_ce_ref(struct cache_entry *ce)
+{
+ assert(ce != NULL && ce->ref_count >= 0);
+ ce->ref_count++;
+}
+
+/*
+ * Decrement the cache_entry reference count. Should be called whenever
+ * a pointer to a cache_entry is dropped. Once the counter drops to 0
+ * the cache_entry memory will be safely freed.
+ */
+static inline void drop_ce_ref(struct cache_entry *ce)
+{
+ if (ce != NULL) {
+ assert(ce->ref_count >= 0);
Shouldn't this be "> 0" to prevent double frees?
No. If the ref_count is 1, then there is still some reference to the
ce. If it is 0, there is no reference to it, and the next check (< 1)
will succeed and the ce will get freed.
+ if (--ce->ref_count < 1) {
+ free(ce);
+ }
+ }
+}
OK, let me think out loud, step by step:
Given ref_count == 1 then the assert passes, ref_count gets decremented
to 0, which is less than 1, so ce is freed.
Given ref_count == 0 then the assert passes, refcount gets decremented
to -1, which is less than 1, so ce is freed again.
Where did I go wrong?
René
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