cfq-iosched: don't call wbt_disable_default() with IRQs disabled

wbt_disable_default() calls del_timer_sync() to wait for the wbt
timer to finish before disabling throttling. We can't do this with
IRQs disable. This fixes a lockdep splat on boot, if non-root
cgroups are used.

Reported-by: Gabriel C <nix.or.die@gmail.com>
Fixes: 87760e5eef35 ("block: hook up writeback throttling")
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index c73a6fcaeb9d52c7e2aa1ebbcf725e86cdc707f4..838f07e2b64a207c0f4d46477a4ffb81d0e4a60b 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3758,7 +3758,7 @@ static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 }
 
 #ifdef CONFIG_CFQ_GROUP_IOSCHED
-static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
+static bool check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
 {
        struct cfq_data *cfqd = cic_to_cfqd(cic);
        struct cfq_queue *cfqq;
@@ -3775,15 +3775,7 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
         * spuriously on a newly created cic but there's no harm.
         */
        if (unlikely(!cfqd) || likely(cic->blkcg_serial_nr == serial_nr))
-               return;
-
-       /*
-        * If we have a non-root cgroup, we can depend on that to
-        * do proper throttling of writes. Turn off wbt for that
-        * case, if it was enabled by default.
-        */
-       if (nonroot_cg)
-               wbt_disable_default(cfqd->queue);
+               return nonroot_cg;
 
        /*
         * Drop reference to queues.  New queues will be assigned in new
@@ -3804,9 +3796,13 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
        }
 
        cic->blkcg_serial_nr = serial_nr;
+       return nonroot_cg;
 }
 #else
-static inline void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio) { }
+static inline bool check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
+{
+       return false;
+}
 #endif  /* CONFIG_CFQ_GROUP_IOSCHED */
 
 static struct cfq_queue **
@@ -4448,11 +4444,12 @@ cfq_set_request(struct request_queue *q, struct request *rq, struct bio *bio,
        const int rw = rq_data_dir(rq);
        const bool is_sync = rq_is_sync(rq);
        struct cfq_queue *cfqq;
+       bool disable_wbt;
 
        spin_lock_irq(q->queue_lock);
 
        check_ioprio_changed(cic, bio);
-       check_blkcg_changed(cic, bio);
+       disable_wbt = check_blkcg_changed(cic, bio);
 new_queue:
        cfqq = cic_to_cfqq(cic, is_sync);
        if (!cfqq || cfqq == &cfqd->oom_cfqq) {
@@ -4488,6 +4485,10 @@ new_queue:
        rq->elv.priv[0] = cfqq;
        rq->elv.priv[1] = cfqq->cfqg;
        spin_unlock_irq(q->queue_lock);
+
+       if (disable_wbt)
+               wbt_disable_default(q);
+
        return 0;
 }