ext4: fix bug_on in ext4_writepages

we got issue as follows:
EXT4-fs error (device loop0): ext4_mb_generate_buddy:1141: group 0, block bitmap and bg descriptor inconsistent: 25 vs 31513 free cls
------------[ cut here ]------------
kernel BUG at fs/ext4/inode.c:2708!
invalid opcode: 0000 [raspberrypi#1] PREEMPT SMP KASAN PTI
CPU: 2 PID: 2147 Comm: rep Not tainted 5.18.0-rc2-next-20220413+ raspberrypi#155
RIP: 0010:ext4_writepages+0x1977/0x1c10
RSP: 0018:ffff88811d3e7880 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffff88811c098000
RDX: 0000000000000000 RSI: ffff88811c098000 RDI: 0000000000000002
RBP: ffff888128140f50 R08: ffffffffb1ff6387 R09: 0000000000000000
R10: 0000000000000007 R11: ffffed10250281ea R12: 0000000000000001
R13: 00000000000000a4 R14: ffff88811d3e7bb8 R15: ffff888128141028
FS:  00007f443aed9740(0000) GS:ffff8883aef00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020007200 CR3: 000000011c2a4000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 do_writepages+0x130/0x3a0
 filemap_fdatawrite_wbc+0x83/0xa0
 filemap_flush+0xab/0xe0
 ext4_alloc_da_blocks+0x51/0x120
 __ext4_ioctl+0x1534/0x3210
 __x64_sys_ioctl+0x12c/0x170
 do_syscall_64+0x3b/0x90

It may happen as follows:
1. write inline_data inode
vfs_write
  new_sync_write
    ext4_file_write_iter
      ext4_buffered_write_iter
        generic_perform_write
          ext4_da_write_begin
            ext4_da_write_inline_data_begin -> If inline data size too
            small will allocate block to write, then mapping will has
            dirty page
                ext4_da_convert_inline_data_to_extent ->clear EXT4_STATE_MAY_INLINE_DATA
2. fallocate
do_vfs_ioctl
  ioctl_preallocate
    vfs_fallocate
      ext4_fallocate
        ext4_convert_inline_data
          ext4_convert_inline_data_nolock
            ext4_map_blocks -> fail will goto restore data
            ext4_restore_inline_data
              ext4_create_inline_data
              ext4_write_inline_data
              ext4_set_inode_state -> set inode EXT4_STATE_MAY_INLINE_DATA
3. writepages
__ext4_ioctl
  ext4_alloc_da_blocks
    filemap_flush
      filemap_fdatawrite_wbc
        do_writepages
          ext4_writepages
            if (ext4_has_inline_data(inode))
              BUG_ON(ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA))

The root cause of this issue is we destory inline data until call
ext4_writepages under delay allocation mode.  But there maybe already
convert from inline to extent.  To solve this issue, we call
filemap_flush first..

Cc: [email protected]
Signed-off-by: Ye Bin <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

Author: Ye Bin

fs/ext4/inline.c

@@ -2005,6 +2005,18 @@ int ext4_convert_inline_data(struct inode *inode)
 	if (!ext4_has_inline_data(inode)) {
 		ext4_clear_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
 		return 0;
+	} else if (!ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)) {
+		/*
+		 * Inode has inline data but EXT4_STATE_MAY_INLINE_DATA is
+		 * cleared. This means we are in the middle of moving of
+		 * inline data to delay allocated block. Just force writeout
+		 * here to finish conversion.
+		 */
+		error = filemap_flush(inode->i_mapping);
+		if (error)
+			return error;
+		if (!ext4_has_inline_data(inode))
+			return 0;
 	}
 
 	needed_blocks = ext4_writepage_trans_blocks(inode);