as-iosched: properly protect ioc_gone and ioc count

If we have multiple tasks freeing io contexts when as-iosched
is being unloaded, we could complete() ioc_gone twice. Fix that by
protecting ioc_gone complete() and clearing with a spinlock for
just that purpose. Doesn't matter from a performance perspective,
since it'll only enter that path when ioc_gone != NULL (when as-iosched
is being rmmod'ed).

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/block/as-iosched.c b/block/as-iosched.c
index 743f33a01a07..9735acb5b4f5 100644
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -151,6 +151,7 @@ enum arq_state {
 
 static DEFINE_PER_CPU(unsigned long, ioc_count);
 static struct completion *ioc_gone;
+static DEFINE_SPINLOCK(ioc_gone_lock);
 
 static void as_move_to_dispatch(struct as_data *ad, struct request *rq);
 static void as_antic_stop(struct as_data *ad);
@@ -164,8 +165,19 @@ static void free_as_io_context(struct as_io_context *aic)
 {
         kfree(aic);
         elv_ioc_count_dec(ioc_count);
-        if (ioc_gone && !elv_ioc_count_read(ioc_count))
-                complete(ioc_gone);
+        if (ioc_gone) {
+                /*
+                 * AS scheduler is exiting, grab exit lock and check
+                 * the pending io context count. If it hits zero,
+                 * complete ioc_gone and set it back to NULL.
+                 */
+                spin_lock(&ioc_gone_lock);
+                if (ioc_gone && !elv_ioc_count_read(ioc_count)) {
+                        complete(ioc_gone);
+                        ioc_gone = NULL;
+                }
+                spin_unlock(&ioc_gone_lock);
+        }
 }
 
 static void as_trim(struct io_context *ioc)
@@ -1493,7 +1505,7 @@ static void __exit as_exit(void)
         /* ioc_gone's update must be visible before reading ioc_count */
         smp_wmb();
         if (elv_ioc_count_read(ioc_count))
-                wait_for_completion(ioc_gone);
+                wait_for_completion(&all_gone);
         synchronize_rcu();
 }