FreeBSD: fix panic due to tqid overflow

The 32-bit counter eventually wraps to 0 which is a sentinel for invalid
id.

Make it 64-bit on LP64 platforms and 0-check otherwise.

Note: Linux counterpart uses id stored per queue instead of a global.
I did not check going that way is feasible with the goal being the
minimal fix doing the job.

Reported by:	YAMAMOTO Shigeru <shigeru@os-hackers.jp>
Reviewed by:	mav
Differential Revision:	https://reviews.freebsd.org/D26759

1 files changed, 32 insertions, 10 deletions

diff --git a/sys/contrib/openzfs/module/os/freebsd/spl/spl_taskq.c b/sys/contrib/openzfs/module/os/freebsd/spl/spl_taskq.c
index 1050816cd968..bc24a562f8fb 100644
--- a/sys/contrib/openzfs/module/os/freebsd/spl/spl_taskq.c
+++ b/sys/contrib/openzfs/module/os/freebsd/spl/spl_taskq.c
@@ -67,7 +67,7 @@ static unsigned long tqenthash;
 static unsigned long tqenthashlock;
 static struct sx *tqenthashtbl_lock;
 
-static uint32_t tqidnext = 1;
+static taskqid_t tqidnext;
 
 #define	TQIDHASH(tqid) (&tqenthashtbl[(tqid) & tqenthash])
 #define	TQIDHASHLOCK(tqid) (&tqenthashtbl_lock[((tqid) & tqenthashlock)])
@@ -90,7 +90,6 @@ system_taskq_init(void *arg)
 	    M_TASKQ, M_WAITOK | M_ZERO);
 	for (i = 0; i < tqenthashlock + 1; i++)
 		sx_init_flags(&tqenthashtbl_lock[i], "tqenthash", SX_DUPOK);
-	tqidnext = 1;
 	taskq_zone = uma_zcreate("taskq_zone", sizeof (taskq_ent_t),
 	    NULL, NULL, NULL, NULL,
 	    UMA_ALIGN_CACHE, 0);
@@ -121,6 +120,28 @@ system_taskq_fini(void *arg)
 SYSUNINIT(system_taskq_fini, SI_SUB_CONFIGURE, SI_ORDER_ANY, system_taskq_fini,
     NULL);
 
+#ifdef __LP64__
+static taskqid_t
+__taskq_genid(void)
+{
+
+	return (atomic_fetchadd_long(&tqidnext, 1) + 1);
+}
+#else
+static taskqid_t
+__taskq_genid(void)
+{
+	taskqid_t tqid;
+
+	for (;;) {
+		tqid = atomic_fetchadd_int(&tqidnext, 1) + 1;
+		if (__predict_true(tqid != 0))
+			break;
+	}
+	return (tqid);
+}
+#endif
+
 static taskq_ent_t *
 taskq_lookup(taskqid_t tqid)
 {
@@ -140,8 +161,10 @@ taskq_lookup(taskqid_t tqid)
 static taskqid_t
 taskq_insert(taskq_ent_t *ent)
 {
-	taskqid_t tqid = atomic_fetchadd_int(&tqidnext, 1);
+	taskqid_t tqid;
 
+	tqid = __taskq_genid();
+	VERIFY(tqid);
 	ent->tqent_id = tqid;
 	ent->tqent_registered = B_TRUE;
 	sx_xlock(TQIDHASHLOCK(tqid));
@@ -289,7 +312,7 @@ taskq_dispatch_delay(taskq_t *tq, task_func_t func, void *arg,
     uint_t flags, clock_t expire_time)
 {
 	taskq_ent_t *task;
-	taskqid_t tid;
+	taskqid_t tqid;
 	clock_t timo;
 	int mflag;
 
@@ -310,13 +333,13 @@ taskq_dispatch_delay(taskq_t *tq, task_func_t func, void *arg,
 	task->tqent_type = TIMEOUT_TASK;
 	task->tqent_cancelled = B_FALSE;
 	refcount_init(&task->tqent_rc, 1);
-	tid = taskq_insert(task);
+	tqid = taskq_insert(task);
 	TIMEOUT_TASK_INIT(tq->tq_queue, &task->tqent_timeout_task, 0,
 	    taskq_run, task);
 
 	taskqueue_enqueue_timeout(tq->tq_queue, &task->tqent_timeout_task,
 	    timo);
-	return (tid);
+	return (tqid);
 }
 
 taskqid_t
@@ -324,7 +347,7 @@ taskq_dispatch(taskq_t *tq, task_func_t func, void *arg, uint_t flags)
 {
 	taskq_ent_t *task;
 	int mflag, prio;
-	taskqid_t tid;
+	taskqid_t tqid;
 
 	if ((flags & (TQ_SLEEP | TQ_NOQUEUE)) == TQ_SLEEP)
 		mflag = M_WAITOK;
@@ -344,11 +367,10 @@ taskq_dispatch(taskq_t *tq, task_func_t func, void *arg, uint_t flags)
 	task->tqent_arg = arg;
 	task->tqent_cancelled = B_FALSE;
 	task->tqent_type = NORMAL_TASK;
-	tid = taskq_insert(task);
+	tqid = taskq_insert(task);
 	TASK_INIT(&task->tqent_task, prio, taskq_run, task);
 	taskqueue_enqueue(tq->tq_queue, &task->tqent_task);
-	VERIFY(tid);
-	return (tid);
+	return (tqid);
 }
 
 static void