elevator: lookup mq vs non-mq elevators

If an IO scheduler is selected via elevator= and it doesn't match
the driver in question wrt blk-mq support, then we fail to boot.

The elevator= parameter is deprecated and only supported for
non-mq devices. Augment the elevator lookup API so that we
pass in if we're looking for an mq capable scheduler or not,
so that we only ever return a valid type for the queue in
question.

Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=196695
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 21 insertions, 23 deletions

diff --git a/block/elevator.c b/block/elevator.c
index 7ae50eb2732b..77856bf29568 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -83,12 +83,15 @@ bool elv_bio_merge_ok(struct request *rq, struct bio *bio)
 }
 EXPORT_SYMBOL(elv_bio_merge_ok);
 
-static struct elevator_type *elevator_find(const char *name)
+/*
+ * Return scheduler with name 'name' and with matching 'mq capability
+ */
+static struct elevator_type *elevator_find(const char *name, bool mq)
 {
         struct elevator_type *e;
 
         list_for_each_entry(e, &elv_list, list) {
-                if (!strcmp(e->elevator_name, name))
+                if (!strcmp(e->elevator_name, name) && (mq == e->uses_mq))
                         return e;
         }
 
@@ -100,25 +103,25 @@ static void elevator_put(struct elevator_type *e)
         module_put(e->elevator_owner);
 }
 
-static struct elevator_type *elevator_get(const char *name, bool try_loading)
+static struct elevator_type *elevator_get(struct request_queue *q,
+                                          const char *name, bool try_loading)
 {
         struct elevator_type *e;
 
         spin_lock(&elv_list_lock);
 
-        e = elevator_find(name);
+        e = elevator_find(name, q->mq_ops != NULL);
         if (!e && try_loading) {
                 spin_unlock(&elv_list_lock);
                 request_module("%s-iosched", name);
                 spin_lock(&elv_list_lock);
-                e = elevator_find(name);
+                e = elevator_find(name, q->mq_ops != NULL);
         }
 
         if (e && !try_module_get(e->elevator_owner))
                 e = NULL;
 
         spin_unlock(&elv_list_lock);
-
         return e;
 }
 
@@ -144,8 +147,12 @@ void __init load_default_elevator_module(void)
         if (!chosen_elevator[0])
                 return;
 
+        /*
+         * Boot parameter is deprecated, we haven't supported that for MQ.
+         * Only look for non-mq schedulers from here.
+         */
         spin_lock(&elv_list_lock);
-        e = elevator_find(chosen_elevator);
+        e = elevator_find(chosen_elevator, false);
         spin_unlock(&elv_list_lock);
 
         if (!e)
@@ -202,7 +209,7 @@ int elevator_init(struct request_queue *q, char *name)
         q->boundary_rq = NULL;
 
         if (name) {
-                e = elevator_get(name, true);
+                e = elevator_get(q, name, true);
                 if (!e)
                         return -EINVAL;
         }
@@ -214,7 +221,7 @@ int elevator_init(struct request_queue *q, char *name)
          * allowed from async.
          */
         if (!e && !q->mq_ops && *chosen_elevator) {
-                e = elevator_get(chosen_elevator, false);
+                e = elevator_get(q, chosen_elevator, false);
                 if (!e)
                         printk(KERN_ERR "I/O scheduler %s not found\n",
                                                         chosen_elevator);
@@ -229,17 +236,17 @@ int elevator_init(struct request_queue *q, char *name)
                  */
                 if (q->mq_ops) {
                         if (q->nr_hw_queues == 1)
-                                e = elevator_get("mq-deadline", false);
+                                e = elevator_get(q, "mq-deadline", false);
                         if (!e)
                                 return 0;
                 } else
-                        e = elevator_get(CONFIG_DEFAULT_IOSCHED, false);
+                        e = elevator_get(q, CONFIG_DEFAULT_IOSCHED, false);
 
                 if (!e) {
                         printk(KERN_ERR
                                 "Default I/O scheduler not found. " \
                                 "Using noop.\n");
-                        e = elevator_get("noop", false);
+                        e = elevator_get(q, "noop", false);
                 }
         }
 
@@ -905,7 +912,7 @@ int elv_register(struct elevator_type *e)
 
         /* register, don't allow duplicate names */
         spin_lock(&elv_list_lock);
-        if (elevator_find(e->elevator_name)) {
+        if (elevator_find(e->elevator_name, e->uses_mq)) {
                 spin_unlock(&elv_list_lock);
                 if (e->icq_cache)
                         kmem_cache_destroy(e->icq_cache);
@@ -1066,7 +1073,7 @@ static int __elevator_change(struct request_queue *q, const char *name)
                 return elevator_switch(q, NULL);
 
         strlcpy(elevator_name, name, sizeof(elevator_name));
-        e = elevator_get(strstrip(elevator_name), true);
+        e = elevator_get(q, strstrip(elevator_name), true);
         if (!e)
                 return -EINVAL;
 
@@ -1076,15 +1083,6 @@ static int __elevator_change(struct request_queue *q, const char *name)
                 return 0;
         }
 
-        if (!e->uses_mq && q->mq_ops) {
-                elevator_put(e);
-                return -EINVAL;
-        }
-        if (e->uses_mq && !q->mq_ops) {
-                elevator_put(e);
-                return -EINVAL;
-        }
-
         return elevator_switch(q, e);
 }