writeback: don't warn on an unregistered BDI in __mark_inode_dirty

mainline inclusion
from mainline-v5.11-rc1
commit f7387170
category: bugfix
bugzilla: 109280
CVE: NA

-----------------------------------------------

BDIs get unregistered during device removal, and this WARN can be
trivially triggered by hot-removing a NVMe device while running fsx
It is otherwise harmless as we still hold a BDI reference, and the
writeback has been shut down already.

Link: https://lore.kernel.org/r/20200928122613.434820-1-hch@lst.deSigned-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJan Kara <jack@suse.cz>

conflicts:
fs/fs-writeback.c
Signed-off-by: NYe Bin <yebin10@huawei.com>
Reviewed-by: NZhang Yi <yi.zhang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/fs-writeback.c

@@ -2219,10 +2219,6 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 
 			wb = locked_inode_to_wb_and_lock_list(inode);
 
-			WARN(bdi_cap_writeback_dirty(wb->bdi) &&
-			     !test_bit(WB_registered, &wb->state),
-			     "bdi-%s not registered\n", wb->bdi->name);
-
 			inode->dirtied_when = jiffies;
 			if (dirtytime)
 				inode->dirtied_time_when = jiffies;