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libmdb: Do not use the MDB_txbody.mtb_txnid field.

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Get txn->mt_txnid from the meta page instead.  Otherwise it
and txn->mt_toggle could become inconsistent, since read-only
txns fetched both from MDB_txbody without mutex proteciton.
This commit is contained in:
Hallvard Furuseth 2012-04-12 07:34:13 +02:00
parent d1738c3e6b
commit 4a0b30499c
1 changed files with 12 additions and 4 deletions
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16
libraries/libmdb/mdb.c
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@ -511,11 +511,17 @@ typedef struct MDB_txbody {
*/
pthread_mutex_t mtb_mutex;
#endif
#if MDB_VERSION == 1
/** The ID of the last transaction committed to the database.
* This is recorded here only for convenience; the value can always
* be determined by reading the main database meta pages.
*
* Value is unused, but maintained for backwards compatibility.
* Drop this or mtb_me_toggle when changing MDB_VERSION.
* (Reading both should have been done atomically.)
*/
txnid_t mtb_txnid;
#endif
/** The number of slots that have been used in the reader table.
* This always records the maximum count, it is not decremented
* when readers release their slots.
@ -536,7 +542,9 @@ typedef struct MDB_txninfo {
#define mti_version mt1.mtb.mtb_version
#define mti_mutex mt1.mtb.mtb_mutex
#define mti_rmname mt1.mtb.mtb_rmname
#if MDB_VERSION == 1
#define mti_txnid mt1.mtb.mtb_txnid
#endif
#define mti_numreaders mt1.mtb.mtb_numreaders
#define mti_me_toggle mt1.mtb.mtb_me_toggle
char pad[(sizeof(MDB_txbody)+CACHELINE-1) & ~(CACHELINE-1)];
@ -1565,18 +1573,19 @@ mdb_txn_renew0(MDB_txn *txn)
pthread_setspecific(env->me_txkey, r);
}
txn->mt_toggle = env->me_txns->mti_me_toggle;
txn->mt_txnid = env->me_txns->mti_txnid;
txn->mt_txnid = r->mr_txnid = env->me_metas[txn->mt_toggle]->mm_txnid;
/* This happens if a different process was the
* last writer to the DB.
*/
if (env->me_wtxnid < txn->mt_txnid)
mt_dbflag = DB_STALE;
r->mr_txnid = txn->mt_txnid;
txn->mt_u.reader = r;
} else {
LOCK_MUTEX_W(env);
txn->mt_txnid = env->me_txns->mti_txnid;
txn->mt_toggle = env->me_txns->mti_me_toggle;
txn->mt_txnid = env->me_metas[txn->mt_toggle]->mm_txnid;
if (env->me_wtxnid < txn->mt_txnid)
mt_dbflag = DB_STALE;
txn->mt_txnid++;
@ -1584,7 +1593,6 @@ mdb_txn_renew0(MDB_txn *txn)
if (txn->mt_txnid == mdb_debug_start)
mdb_debug = 1;
#endif
txn->mt_toggle = env->me_txns->mti_me_toggle;
txn->mt_u.dirty_list = env->me_dirty_list;
txn->mt_u.dirty_list[0].mid = 0;
txn->mt_free_pgs = env->me_free_pgs;