[PATCH 1/2] iosched: fix typo and barrier()
On rmmod path, cfq/as waits to make sure all io-contexts was
freed. However, it's using complete(), not wait_for_completion().
I think barrier() is not enough in here. To avoid the following case,
this patch replaces barrier() with smb_wmb().
cpu0 visibility cpu1
[ioc_gnone=NULL,ioc_count=1]
ioc_gnone = &all_gone NULL,ioc_count=1
atomic_read(&ioc_count) NULL,ioc_count=1
wait_for_completion() NULL,ioc_count=0 atomic_sub_and_test()
NULL,ioc_count=0 if ( && ioc_gone)
[ioc_gone==NULL,
so doesn't call complete()]
&all_gone,ioc_count=0
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Jens Axboe <axboe@suse.de>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 67d446d..01820b1 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2439,9 +2439,10 @@
DECLARE_COMPLETION(all_gone);
elv_unregister(&iosched_cfq);
ioc_gone = &all_gone;
- barrier();
+ /* ioc_gone's update must be visible before reading ioc_count */
+ smp_wmb();
if (atomic_read(&ioc_count))
- complete(ioc_gone);
+ wait_for_completion(ioc_gone);
synchronize_rcu();
cfq_slab_kill();
}