blk-stat: don't use this_cpu_ptr() in a preemptable section

If PREEMPT_RCU is enabled, rcu_read_lock() isn't strong enough
for us to use this_cpu_ptr() in that section. Use the safer
get/put_cpu_ptr() variants instead.

Reported-by: Mike Galbraith <efault@gmx.de>
Fixes: 34dbad5d26e2 ("blk-stat: convert to callback-based statistics reporting")
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 10 insertions, 7 deletions

diff --git a/block/blk-stat.c b/block/blk-stat.c
index 6c2f40940439..c52356d90fe3 100644
--- a/block/blk-stat.c
+++ b/block/blk-stat.c
@@ -96,13 +96,16 @@ void blk_stat_add(struct request *rq)
 
         rcu_read_lock();
         list_for_each_entry_rcu(cb, &q->stats->callbacks, list) {
-                if (blk_stat_is_active(cb)) {
-                        bucket = cb->bucket_fn(rq);
-                        if (bucket < 0)
-                                continue;
-                        stat = &this_cpu_ptr(cb->cpu_stat)[bucket];
-                        __blk_stat_add(stat, value);
-                }
+                if (!blk_stat_is_active(cb))
+                        continue;
+
+                bucket = cb->bucket_fn(rq);
+                if (bucket < 0)
+                        continue;
+
+                stat = &get_cpu_ptr(cb->cpu_stat)[bucket];
+                __blk_stat_add(stat, value);
+                put_cpu_ptr(cb->cpu_stat);
         }
         rcu_read_unlock();
 }