Subclass tq_lock to eliminate a lockdep warning

When taskq_dispatch() calls taskq_thread_spawn() to create a new thread
for a taskq, linux lockdep warns of possible recursive locking.  This is
a false positive.

One such call chain is as follows, when a taskq needs more threads:
	taskq_dispatch->taskq_thread_spawn->taskq_dispatch

The initial taskq_dispatch() holds tq_lock on the taskq that needed more
worker threads.  The later call into taskq_dispatch() takes
dynamic_taskq->tq_lock.  Without subclassing, lockdep believes these
could potentially be the same lock and complains.  A similar case occurs
when taskq_dispatch() then calls task_alloc().

This patch uses spin_lock_irqsave_nested() when taking tq_lock, with one
of two new lock subclasses:

subclass              taskq
TQ_LOCK_DYNAMIC       dynamic_taskq
TQ_LOCK_GENERAL       any other

Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #480

diff --git a/include/sys/taskq.h b/include/sys/taskq.h
index a43a86da651470d42ffc7858164a620e7d516146..5830fe2dd1b3cd9d90a71ef929c38f1bd3c93e93 100644 (file)
--- a/include/sys/taskq.h
+++ b/include/sys/taskq.h
@@ -55,6 +55,14 @@
 #define TQ_NEW                 0x04000000
 #define TQ_FRONT               0x08000000
 
+/* spin_lock(lock) and spin_lock_nested(lock,0) are equivalent,
+ * so TQ_LOCK_DYNAMIC must not evaluate to 0
+ */
+typedef enum tq_lock_role {
+       TQ_LOCK_GENERAL =       0,
+       TQ_LOCK_DYNAMIC =       1,
+} tq_lock_role_t;
+
 typedef unsigned long taskqid_t;
 typedef void (task_func_t)(void *);
 
@@ -81,6 +89,7 @@ typedef struct taskq {
        struct list_head        tq_delay_list; /* delayed task_t's */
        wait_queue_head_t       tq_work_waitq; /* new work waitq */
        wait_queue_head_t       tq_wait_waitq; /* wait waitq */
+       tq_lock_role_t          tq_lock_class; /* class used when taking tq_lock */
 } taskq_t;
 
 typedef struct taskq_ent {

diff --git a/module/spl/spl-taskq.c b/module/spl/spl-taskq.c
index 2c2e3ad465abc2fad764816edb53723892595db6..588dbc8a4044b52e1d2ec3b1fe8e012b2ce73076 100644 (file)
--- a/module/spl/spl-taskq.c
+++ b/module/spl/spl-taskq.c
@@ -113,7 +113,8 @@ retry:
                 */
                spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
                schedule_timeout(HZ / 100);
-               spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+               spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+                   tq->tq_lock_class);
                if (count < 100) {
                        count++;
                        goto retry;
@@ -122,7 +123,8 @@ retry:
 
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
        t = kmem_alloc(sizeof(taskq_ent_t), task_km_flags(flags));
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
 
        if (t) {
                taskq_init_ent(t);
@@ -188,7 +190,8 @@ task_expire(unsigned long data)
        taskq_t *tq = t->tqent_taskq;
        struct list_head *l;
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
 
        if (t->tqent_flags & TQENT_FLAG_CANCEL) {
                ASSERT(list_empty(&t->tqent_list));
@@ -379,7 +382,8 @@ taskq_wait_id_check(taskq_t *tq, taskqid_t id)
        int active = 0;
        int rc;
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
        rc = (taskq_find(tq, id, &active) == NULL);
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
 
@@ -402,7 +406,8 @@ taskq_wait_outstanding_check(taskq_t *tq, taskqid_t id)
 {
        int rc;
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
        rc = (id < tq->tq_lowest_id);
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
 
@@ -429,7 +434,8 @@ taskq_wait_check(taskq_t *tq)
 {
        int rc;
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
        rc = (tq->tq_lowest_id == tq->tq_next_id);
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
 
@@ -474,7 +480,8 @@ taskq_member(taskq_t *tq, void *t)
 {
        int found;
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
        found = taskq_member_impl(tq, t);
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
 
@@ -497,7 +504,8 @@ taskq_cancel_id(taskq_t *tq, taskqid_t id)
 
        ASSERT(tq);
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
        t = taskq_find(tq, id, &active);
        if (t && !active) {
                list_del_init(&t->tqent_list);
@@ -519,7 +527,8 @@ taskq_cancel_id(taskq_t *tq, taskqid_t id)
                if (timer_pending(&t->tqent_timer)) {
                        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
                        del_timer_sync(&t->tqent_timer);
-                       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+                       spin_lock_irqsave_nested(&tq->tq_lock,
+                           tq->tq_lock_flags, tq->tq_lock_class);
                }
 
                if (!(t->tqent_flags & TQENT_FLAG_PREALLOC))
@@ -549,7 +558,8 @@ taskq_dispatch(taskq_t *tq, task_func_t func, void *arg, uint_t flags)
        ASSERT(tq);
        ASSERT(func);
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
 
        /* Taskq being destroyed and all tasks drained */
        if (!(tq->tq_flags & TASKQ_ACTIVE))
@@ -605,7 +615,8 @@ taskq_dispatch_delay(taskq_t *tq, task_func_t func, void *arg,
        ASSERT(tq);
        ASSERT(func);
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
 
        /* Taskq being destroyed and all tasks drained */
        if (!(tq->tq_flags & TASKQ_ACTIVE))
@@ -648,7 +659,8 @@ taskq_dispatch_ent(taskq_t *tq, task_func_t func, void *arg, uint_t flags,
        ASSERT(tq);
        ASSERT(func);
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
 
        /* Taskq being destroyed and all tasks drained */
        if (!(tq->tq_flags & TASKQ_ACTIVE)) {
@@ -740,13 +752,14 @@ taskq_thread_spawn_task(void *arg)
 
        (void) taskq_thread_create(tq);
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
        tq->tq_nspawn--;
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
 }
 
 /*
- * Spawn addition threads for dynamic taskqs (TASKQ_DYNMAIC) the current
+ * Spawn addition threads for dynamic taskqs (TASKQ_DYNAMIC) the current
  * number of threads is insufficient to handle the pending tasks.  These
  * new threads must be created by the dedicated dynamic_taskq to avoid
  * deadlocks between thread creation and memory reclaim.  The system_taskq
@@ -810,6 +823,7 @@ taskq_thread(void *args)
        int seq_tasks = 0;
 
        ASSERT(tqt);
+       ASSERT(tqt->tqt_tq);
        tq = tqt->tqt_tq;
        current->flags |= PF_NOFREEZE;
 
@@ -821,7 +835,8 @@ taskq_thread(void *args)
        sigprocmask(SIG_BLOCK, &blocked, NULL);
        flush_signals(current);
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
 
        /* Immediately exit if more threads than allowed were created. */
        if (tq->tq_nthreads >= tq->tq_maxthreads)
@@ -848,7 +863,8 @@ taskq_thread(void *args)
                        schedule();
                        seq_tasks = 0;
 
-                       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+                       spin_lock_irqsave_nested(&tq->tq_lock,
+                           tq->tq_lock_flags, tq->tq_lock_class);
                        remove_wait_queue(&tq->tq_work_waitq, &wait);
                } else {
                        __set_current_state(TASK_RUNNING);
@@ -877,7 +893,8 @@ taskq_thread(void *args)
                        /* Perform the requested task */
                        t->tqent_func(t->tqent_arg);
 
-                       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+                       spin_lock_irqsave_nested(&tq->tq_lock,
+                           tq->tq_lock_flags, tq->tq_lock_class);
                        tq->tq_nactive--;
                        list_del_init(&tqt->tqt_active_list);
                        tqt->tqt_task = NULL;
@@ -999,9 +1016,11 @@ taskq_create(const char *name, int nthreads, pri_t pri,
        INIT_LIST_HEAD(&tq->tq_delay_list);
        init_waitqueue_head(&tq->tq_work_waitq);
        init_waitqueue_head(&tq->tq_wait_waitq);
+       tq->tq_lock_class = TQ_LOCK_GENERAL;
 
        if (flags & TASKQ_PREPOPULATE) {
-               spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+               spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+                   tq->tq_lock_class);
 
                for (i = 0; i < minalloc; i++)
                        task_done(tq, task_alloc(tq, TQ_PUSHPAGE | TQ_NEW));
@@ -1040,7 +1059,8 @@ taskq_destroy(taskq_t *tq)
        taskq_ent_t *t;
 
        ASSERT(tq);
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
        tq->tq_flags &= ~TASKQ_ACTIVE;
        spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
 
@@ -1053,7 +1073,8 @@ taskq_destroy(taskq_t *tq)
 
        taskq_wait(tq);
 
-       spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+       spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+           tq->tq_lock_class);
 
        /*
         * Signal each thread to exit and block until it does.  Each thread
@@ -1069,7 +1090,8 @@ taskq_destroy(taskq_t *tq)
 
                kthread_stop(thread);
 
-               spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
+               spin_lock_irqsave_nested(&tq->tq_lock, tq->tq_lock_flags,
+                   tq->tq_lock_class);
        }
 
        while (!list_empty(&tq->tq_free_list)) {
@@ -1113,6 +1135,12 @@ spl_taskq_init(void)
                return (1);
        }
 
+       /* This is used to annotate tq_lock, so
+        *      taskq_dispatch -> taskq_thread_spawn -> taskq_dispatch
+        * does not trigger a lockdep warning re: possible recursive locking
+        */
+       dynamic_taskq->tq_lock_class = TQ_LOCK_DYNAMIC;
+
        return (0);
 }