Never, *ever* hold a mutex lock in the message database where there may

be traversals being attempted. Yes, this was from bitter experience (and
an out of control server :-). Also allow callers to break out of a tdb_chainlock
with sigalarm if desired.
Jeremy.
(This used to be commit a7781f91d8c1177210bffc199cd2f3b7ff993eaf)

3 files changed, 17 insertions, 0 deletions

diff --git a/source3/tdb/tdb.c b/source3/tdb/tdb.c
index 40e7dcd42c..5bb75ffe07 100644
--- a/source3/tdb/tdb.c
+++ b/source3/tdb/tdb.c
@@ -34,6 +34,7 @@
 #include <errno.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
+#include <signal.h>
 #include "tdb.h"
 #include "spinlock.h"
 #else
@@ -160,6 +161,18 @@ struct list_struct {
 	*/
 };
 
+/***************************************************************
+ Allow a caller to set a "alarm" flag that tdb can check to abort
+ a blocking lock on SIGALRM.
+***************************************************************/
+
+static sig_atomic_t *palarm_fired;
+
+void tdb_set_lock_alarm(sig_atomic_t *palarm)
+{
+	palarm_fired = palarm;
+}
+
 /* a byte range locking function - return 0 on success
    this functions locks/unlocks 1 byte at the specified offset.
 
@@ -186,6 +199,8 @@ static int tdb_brlock(TDB_CONTEXT *tdb, tdb_off offset,
 
 	do {
 		ret = fcntl(tdb->fd,lck_type,&fl);
+		if (ret == -1 && errno == EINTR && palarm_fired && *palarm_fired)
+			break;
 	} while (ret == -1 && errno == EINTR);
 
 	if (ret == -1) {
diff --git a/source3/tdb/tdb.h b/source3/tdb/tdb.h
index 8cc908703f..42b88aeb16 100644
--- a/source3/tdb/tdb.h
+++ b/source3/tdb/tdb.h
@@ -126,6 +126,7 @@ int tdb_lockall(TDB_CONTEXT *tdb);
 void tdb_unlockall(TDB_CONTEXT *tdb);
 
 /* Low level locking functions: use with care */
+void tdb_set_lock_alarm(sig_atomic_t *palarm);
 int tdb_chainlock(TDB_CONTEXT *tdb, TDB_DATA key);
 int tdb_chainunlock(TDB_CONTEXT *tdb, TDB_DATA key);
 
diff --git a/source3/tdb/tdbbackup.c b/source3/tdb/tdbbackup.c
index f59f98a90f..36ba7db918 100644
--- a/source3/tdb/tdbbackup.c
+++ b/source3/tdb/tdbbackup.c
@@ -53,6 +53,7 @@
 #include <sys/stat.h>
 #include <sys/time.h>
 #include <ctype.h>
+#include <signal.h>
 #include "tdb.h"
 
 static int failed;