blk-cgroup: increase number of supported policies

After merging the iolatency policy, we potentially now have 4 policies
being registered, but only support 3. This causes one of them to fail
loading. Takashi reports that BFQ no longer works for him, because it
fails to load due to policy registration failure.

Bump to 5 policies, and also add a warning for when we have exceeded
the global amount. If we have to touch this again, we should switch
to a dynamic scheme instead.

Reported-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Tested-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 4 insertions, 2 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index c19f9078da1e..c630e02836a8 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1510,8 +1510,10 @@ int blkcg_policy_register(struct blkcg_policy *pol)
         for (i = 0; i < BLKCG_MAX_POLS; i++)
                 if (!blkcg_policy[i])
                         break;
-        if (i >= BLKCG_MAX_POLS)
+        if (i >= BLKCG_MAX_POLS) {
+                pr_warn("blkcg_policy_register: BLKCG_MAX_POLS too small\n");
                 goto err_unlock;
+        }
 
         /* Make sure cpd/pd_alloc_fn and cpd/pd_free_fn in pairs */
         if ((!pol->cpd_alloc_fn ^ !pol->cpd_free_fn) ||
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index d6869e0e2b64..6980014357d4 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -54,7 +54,7 @@ struct blk_stat_callback;
  * Maximum number of blkcg policies allowed to be registered concurrently.
  * Defined here to simplify include dependency.
  */
-#define BLKCG_MAX_POLS          3
+#define BLKCG_MAX_POLS          5
 
 typedef void (rq_end_io_fn)(struct request *, blk_status_t);