From: Eric Wheeler Date: Fri, 26 Feb 2016 22:39:06 +0000 (-0800) Subject: bcache: fix race of writeback thread starting before complete initialization X-Git-Tag: firefly_0821_release~176^2~4^2~50^2~87 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=b58e781068d9a5fd6b0ee77f595c3dbaa0d2b7aa;p=firefly-linux-kernel-4.4.55.git bcache: fix race of writeback thread starting before complete initialization commit 07cc6ef8edc47f8b4fc1e276d31127a0a5863d4d upstream. The bch_writeback_thread might BUG_ON in read_dirty() if dc->sb==BDEV_STATE_DIRTY and bch_sectors_dirty_init has not yet completed its related initialization. This patch downs the dc->writeback_lock until after initialization is complete, thus preventing bch_writeback_thread from proceeding prematurely. See this thread: http://thread.gmane.org/gmane.linux.kernel.bcache.devel/3453 Signed-off-by: Eric Wheeler Tested-by: Marc MERLIN Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index f3f98c3d7f67..6b07a0c8c729 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -1015,8 +1015,12 @@ int bch_cached_dev_attach(struct cached_dev *dc, struct cache_set *c) */ atomic_set(&dc->count, 1); - if (bch_cached_dev_writeback_start(dc)) + /* Block writeback thread, but spawn it */ + down_write(&dc->writeback_lock); + if (bch_cached_dev_writeback_start(dc)) { + up_write(&dc->writeback_lock); return -ENOMEM; + } if (BDEV_STATE(&dc->sb) == BDEV_STATE_DIRTY) { bch_sectors_dirty_init(dc); @@ -1028,6 +1032,9 @@ int bch_cached_dev_attach(struct cached_dev *dc, struct cache_set *c) bch_cached_dev_run(dc); bcache_device_link(&dc->disk, c, "bdev"); + /* Allow the writeback thread to proceed */ + up_write(&dc->writeback_lock); + pr_info("Caching %s as %s on set %pU", bdevname(dc->bdev, buf), dc->disk.disk->disk_name, dc->disk.c->sb.set_uuid);