[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/as-iosched.c b/block/as-iosched.c
index 296708c..e25a5d7 100644 (file)
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -1844,9 +1844,10 @@ static void __exit as_exit(void)
        DECLARE_COMPLETION(all_gone);
        elv_unregister(&iosched_as);
        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();
        kmem_cache_destroy(arq_pool);
 }

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 67d446d..01820b1 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2439,9 +2439,10 @@ static void __exit cfq_exit(void)
        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();
 }