ext4: move percpu_rwsem protection into ext4_writepages()

Move protection by percpu_rwsem from ext4_do_writepages() to
ext4_writepages(). We will not want to grab this protection during
transaction commits as that would be prone to deadlocks and the
protection is not needed. Move the shutdown state checking as well since
we want to be able to complete commit while the shutdown is in progress.

Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20221207112722.22220-7-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/inode.c

@@ -2727,10 +2727,6 @@ static int ext4_do_writepages(struct mpage_da_data *mpd)
 	struct blk_plug plug;
 	bool give_up_on_write = false;
 
-	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
-		return -EIO;
-
-	percpu_down_read(&sbi->s_writepages_rwsem);
 	trace_ext4_writepages(inode, wbc);
 
 	/*
@@ -2940,20 +2936,28 @@ static int ext4_do_writepages(struct mpage_da_data *mpd)
 out_writepages:
 	trace_ext4_writepages_result(inode, wbc, ret,
 				     nr_to_write - wbc->nr_to_write);
-	percpu_up_read(&sbi->s_writepages_rwsem);
 	return ret;
 }
 
 static int ext4_writepages(struct address_space *mapping,
 			   struct writeback_control *wbc)
 {
+	struct super_block *sb = mapping->host->i_sb;
 	struct mpage_da_data mpd = {
 		.inode = mapping->host,
 		.wbc = wbc,
 		.can_map = 1,
 	};
+	int ret;
+
+	if (unlikely(ext4_forced_shutdown(EXT4_SB(sb))))
+		return -EIO;
 
-	return ext4_do_writepages(&mpd);
+	percpu_down_read(&EXT4_SB(sb)->s_writepages_rwsem);
+	ret = ext4_do_writepages(&mpd);
+	percpu_up_read(&EXT4_SB(sb)->s_writepages_rwsem);
+
+	return ret;
 }
 
 static int ext4_dax_writepages(struct address_space *mapping,