buffer: clear BH_Write_EIO when a buffer is forgotten

BH_Write_EIO records that the last write of this buffer failed.  It is
cleared when the buffer is written again, but a filesystem freeing a
metadata block never writes it again.  It calls bforget() and hands the
block back to the allocator, so the flag outlives the block it refers to.

That does not matter much today, because the write error is also recorded
by clearing BH_Uptodate and the buffer is discarded soon after.  It starts
to matter in the rest of this series, which stops clearing BH_Uptodate on
write error and makes BH_Write_EIO the way a failed metadata write is
reported.

bforget() is where a filesystem says it no longer cares about this
buffer's contents, so clear the error there alongside the dirty flag.

Suggested-by: Jan Kara <jack@suse.cz>
Acked-by: Weidong Zhu <weizhu@fiu.edu>
Signed-off-by: Chao Shi <coshi036@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/ebe0b4f179ccdac7a9400fe2611623ce218c8d87.1785951556.git.coshi036@gmail.com
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

fs/buffer.c

@@ -1062,6 +1062,7 @@ EXPORT_SYMBOL(__brelse);
 void __bforget(struct buffer_head *bh)
 {
 	clear_buffer_dirty(bh);
+	clear_buffer_write_io_error(bh);
 	remove_assoc_queue(bh);
 	__brelse(bh);
 }