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authorVolker Lendecke <vl@samba.org>2012-01-08 19:04:39 +0100
committerVolker Lendecke <vlendec@samba.org>2012-01-18 14:48:04 +0100
commit333c92384b0680b8f8e5198dd68d49b249b34ec7 (patch)
tree8042feeb87bf2a0f763b0972facca268a935a8c6 /source3
parent45e61fcf61ed9863fbe2b116fe0763fc139bbe0d (diff)
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s3: Enforce a lock order in dbwrap
This makes sure we do not deadlock from doing two dbwrap_fetch_locked in two processes in different orders. At open time, we assign a strict order to all databases. lock_order 1 will be locked first, lock_order 2 second. No two records of the same lock order may be locked at the same time.
Diffstat (limited to 'source3')
-rw-r--r--source3/lib/dbwrap/dbwrap.c81
-rw-r--r--source3/lib/dbwrap/dbwrap_open.c3
-rw-r--r--source3/lib/dbwrap/dbwrap_private.h1
-rw-r--r--source3/lib/dbwrap/dbwrap_rbt.c1
4 files changed, 85 insertions, 1 deletions
diff --git a/source3/lib/dbwrap/dbwrap.c b/source3/lib/dbwrap/dbwrap.c
index c551bfdeca..e443fa5eb3 100644
--- a/source3/lib/dbwrap/dbwrap.c
+++ b/source3/lib/dbwrap/dbwrap.c
@@ -75,11 +75,90 @@ NTSTATUS dbwrap_record_delete(struct db_record *rec)
return rec->delete_rec(rec);
}
+struct dbwrap_lock_order_state {
+ uint8_t *plock_order_mask;
+ uint8_t bitmask;
+};
+
+static int dbwrap_lock_order_state_destructor(
+ struct dbwrap_lock_order_state *s)
+{
+ *s->plock_order_mask &= ~s->bitmask;
+ return 0;
+}
+
+static struct dbwrap_lock_order_state *dbwrap_check_lock_order(
+ struct db_context *db, TALLOC_CTX *mem_ctx)
+{
+ /*
+ * Store the lock_order of currently locked records as bits in
+ * "lock_order_mask". We only use levels 1,2,3 right now, so a
+ * single uint8_t is enough.
+ */
+ static uint8_t lock_order_mask;
+
+ struct dbwrap_lock_order_state *state;
+ uint8_t idx;
+ int used;
+
+ if (db->lock_order == 0) {
+ /*
+ * lock order 0 is for example for dbwrap_rbt without
+ * real locking. Return state nevertheless to avoid
+ * special cases.
+ */
+ return talloc(mem_ctx, struct dbwrap_lock_order_state);
+ }
+
+ /*
+ * We fill bits from the high bits, to be able to use
+ * "ffs(lock_order_mask)"
+ */
+ idx = sizeof(lock_order_mask)*8 - db->lock_order;
+
+ used = ffs(lock_order_mask);
+
+ DEBUG(1, ("used=%d, lock_order=%d, idx=%d\n", used,
+ (int)db->lock_order, (int)idx));
+
+ if ((used != 0) && (used-1 <= idx)) {
+ DEBUG(0, ("Lock order violation: Trying %d, order_mask=%x\n",
+ (int)db->lock_order, (int)lock_order_mask));
+ return NULL;
+ }
+
+ state = talloc(mem_ctx, struct dbwrap_lock_order_state);
+ if (state == NULL) {
+ DEBUG(1, ("talloc failed\n"));
+ return NULL;
+ }
+ state->bitmask = 1 << idx;
+ state->plock_order_mask = &lock_order_mask;
+
+ talloc_set_destructor(state, dbwrap_lock_order_state_destructor);
+ lock_order_mask |= state->bitmask;
+
+ return state;
+}
+
struct db_record *dbwrap_fetch_locked(struct db_context *db,
TALLOC_CTX *mem_ctx,
TDB_DATA key)
{
- return db->fetch_locked(db, mem_ctx, key);
+ struct db_record *rec;
+ struct dbwrap_lock_order_state *lock_order;
+
+ lock_order = dbwrap_check_lock_order(db, talloc_tos());
+ if (lock_order == NULL) {
+ return NULL;
+ }
+ rec = db->fetch_locked(db, mem_ctx, key);
+ if (rec == NULL) {
+ TALLOC_FREE(lock_order);
+ return NULL;
+ }
+ (void)talloc_steal(rec, lock_order);
+ return rec;
}
struct dbwrap_fetch_state {
diff --git a/source3/lib/dbwrap/dbwrap_open.c b/source3/lib/dbwrap/dbwrap_open.c
index 23d299511b..af24ed8847 100644
--- a/source3/lib/dbwrap/dbwrap_open.c
+++ b/source3/lib/dbwrap/dbwrap_open.c
@@ -124,5 +124,8 @@ struct db_context *db_open(TALLOC_CTX *mem_ctx,
result = db_open_tdb(mem_ctx, name, hash_size,
tdb_flags, open_flags, mode);
}
+ if (result != NULL) {
+ result->lock_order = lock_order;
+ }
return result;
}
diff --git a/source3/lib/dbwrap/dbwrap_private.h b/source3/lib/dbwrap/dbwrap_private.h
index d0b3279368..111f02dc6b 100644
--- a/source3/lib/dbwrap/dbwrap_private.h
+++ b/source3/lib/dbwrap/dbwrap_private.h
@@ -56,6 +56,7 @@ struct db_context {
int (*exists)(struct db_context *db,TDB_DATA key);
int (*wipe)(struct db_context *db);
void *private_data;
+ enum dbwrap_lock_order lock_order;
bool persistent;
};
diff --git a/source3/lib/dbwrap/dbwrap_rbt.c b/source3/lib/dbwrap/dbwrap_rbt.c
index 2460418d1d..4fbb0bc1a0 100644
--- a/source3/lib/dbwrap/dbwrap_rbt.c
+++ b/source3/lib/dbwrap/dbwrap_rbt.c
@@ -435,6 +435,7 @@ struct db_context *db_open_rbt(TALLOC_CTX *mem_ctx)
result->exists = db_rbt_exists;
result->wipe = db_rbt_wipe;
result->parse_record = db_rbt_parse_record;
+ result->lock_order = 0;
return result;
}