ext4: fix warning in ext4_handle_inode_extension

We got issue as follows:
EXT4-fs error (device loop0) in ext4_reserve_inode_write:5741: Out of memory
EXT4-fs error (device loop0): ext4_setattr:5462: inode #13: comm syz-executor.0: mark_inode_dirty error
EXT4-fs error (device loop0) in ext4_setattr:5519: Out of memory
EXT4-fs error (device loop0): ext4_ind_map_blocks:595: inode #13: comm syz-executor.0: Can't allocate blocks for non-extent mapped inodes with bigalloc
------------[ cut here ]------------
WARNING: CPU: 1 PID: 4361 at fs/ext4/file.c:301 ext4_file_write_iter+0x11c9/0x1220
Modules linked in:
CPU: 1 PID: 4361 Comm: syz-executor.0 Not tainted 5.10.0+ #1
RIP: 0010:ext4_file_write_iter+0x11c9/0x1220
RSP: 0018:ffff924d80b27c00 EFLAGS: 00010282
RAX: ffffffff815a3379 RBX: 0000000000000000 RCX: 000000003b000000
RDX: ffff924d81601000 RSI: 00000000000009cc RDI: 00000000000009cd
RBP: 000000000000000d R08: ffffffffbc5a2c6b R09: 0000902e0e52a96f
R10: ffff902e2b7c1b40 R11: ffff902e2b7c1b40 R12: 000000000000000a
R13: 0000000000000001 R14: ffff902e0e52aa10 R15: ffffffffffffff8b
FS:  00007f81a7f65700(0000) GS:ffff902e3bc80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600400 CR3: 000000012db88001 CR4: 00000000003706e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 do_iter_readv_writev+0x2e5/0x360
 do_iter_write+0x112/0x4c0
 do_pwritev+0x1e5/0x390
 __x64_sys_pwritev2+0x7e/0xa0
 do_syscall_64+0x37/0x50
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Above issue may happen as follows:
Assume
inode.i_size=4096
EXT4_I(inode)->i_disksize=4096

step 1: set inode->i_isize = 8192
ext4_setattr
  if (attr->ia_size != inode->i_size)
    EXT4_I(inode)->i_disksize = attr->ia_size;
    rc = ext4_mark_inode_dirty
       ext4_reserve_inode_write
          ext4_get_inode_loc
            __ext4_get_inode_loc
              sb_getblk --> return -ENOMEM
   ...
   if (!error)  ->will not update i_size
     i_size_write(inode, attr->ia_size);
Now:
inode.i_size=4096
EXT4_I(inode)->i_disksize=8192

step 2: Direct write 4096 bytes
ext4_file_write_iter
 ext4_dio_write_iter
   iomap_dio_rw ->return error
 if (extend)
   ext4_handle_inode_extension
     WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize);
->Then trigger warning.

To solve above issue, if mark inode dirty failed in ext4_setattr just
set 'EXT4_I(inode)->i_disksize' with old value.
Signed-off-by: Ye Bin <yebin10@huawei.com>
Link: https://lore.kernel.org/r/20220326065351.761952-1-yebin10@huawei.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

fs/ext4/inode.c

@@ -5398,6 +5398,7 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 	if (attr->ia_valid & ATTR_SIZE) {
 		handle_t *handle;
 		loff_t oldsize = inode->i_size;
+		loff_t old_disksize;
 		int shrink = (attr->ia_size < inode->i_size);
 
 		if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
@@ -5469,6 +5470,7 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 					inode->i_sb->s_blocksize_bits);
 
 			down_write(&EXT4_I(inode)->i_data_sem);
+			old_disksize = EXT4_I(inode)->i_disksize;
 			EXT4_I(inode)->i_disksize = attr->ia_size;
 			rc = ext4_mark_inode_dirty(handle, inode);
 			if (!error)
@@ -5480,6 +5482,8 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 			 */
 			if (!error)
 				i_size_write(inode, attr->ia_size);
+			else
+				EXT4_I(inode)->i_disksize = old_disksize;
 			up_write(&EXT4_I(inode)->i_data_sem);
 			ext4_journal_stop(handle);
 			if (error)