[PATCH 1/2] iosched: fix typo and barrier() (fba82272) · Commits · 戴 / test

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>

block/as-iosched.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -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);
		}

block/cfq-iosched.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -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();
		}

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