inode.i_size=4096
EXT4_I(inode)->i_disksize=4096
第一步把文件大小变成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); 

inode.i_size=4096
EXT4_I(inode)->i_disksize=8192

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);

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

WARNING: CPU: 1 PID: 4361 at fs/ext4/file.c:301 ext4_handle_inode_extension fs/ext4/file.c:301 [inline]
WARNING: CPU: 1 PID: 4361 at fs/ext4/file.c:301 ext4_dio_write_iter fs/ext4/file.c:575 [inline]
WARNING: CPU: 1 PID: 4361 at fs/ext4/file.c:301 ext4_file_write_iter+0x11c9/0x1220 fs/ext4/file.c:679
Modules linked in:
CPU: 1 PID: 4361 Comm: syz-executor.0 Not tainted 5.10.0+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
RIP: 0010:ext4_handle_inode_extension fs/ext4/file.c:301 [inline]
RIP: 0010:ext4_dio_write_iter fs/ext4/file.c:575 [inline]
RIP: 0010:ext4_file_write_iter+0x11c9/0x1220 fs/ext4/file.c:679
Code: ff e8 eb 47 ca ff 49 c7 c5 ff ff ff ff e9 9e f6 ff ff e8 da 47 ca ff 49 c7 c5 ff ff ff ff 31 ed e9 61 f6 ff ff e8 c7 47 ca ff <0f> 0b 48 8b 5c 24 18 48 89 df e8 d8 23 d2 ff 48 8b 2b e9 e9 f8 ff
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 fs/read_write.c:732
 do_iter_write+0x112/0x4c0 fs/read_write.c:861
 vfs_writev fs/read_write.c:934 [inline]
 do_pwritev+0x1e5/0x390 fs/read_write.c:1031
 __do_sys_pwritev2 fs/read_write.c:1090 [inline]
 __se_sys_pwritev2 fs/read_write.c:1081 [inline]
 __x64_sys_pwritev2+0x7e/0xa0 fs/read_write.c:1081
 do_syscall_64+0x37/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x46b5e9
Code: 5d db fa ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 2b db fa ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f81a7f64c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 000000000077bf60 RCX: 000000000046b5e9
RDX: 0000000000000001 RSI: 0000000020000a40 RDI: 0000000000000003
RBP: 000000000077bf60 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffe2d25b08f R14: 00007f81a7f659c0 R15: 000000000077bf6c
---[ end trace 76ee148b904e722c ]---
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
serio: Serial port tty23
EXT4-fs (loop0): warning: mounting unchecked fs, running e2fsck is recommended
FAT-fs (loop2): bogus number of reserved sectors
FAT-fs (loop2): Can't find a valid FAT filesystem
EXT4-fs (loop0): mounted filesystem without journal. Opts: ,errors=continue
EXT4-fs (loop1): warning: mounting unchecked fs, running e2fsck is recommended
EXT4-fs (loop1): mounted filesystem without journal. Opts: ,errors=continue
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
FAT-fs (loop2): bogus number of reserved sectors
FAT-fs (loop2): Can't find a valid FAT filesystem
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
EXT4-fs (loop1): 1 orphan inode deleted
EXT4-fs (loop1): mounted filesystem without journal. Opts: ,errors=continue