f2fs: fix f2fs_bug_on when uninstalling filesystem call f2fs_evict_inode.

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix f2fs_bug_on when uninstalling filesystem call f2fs_evict_inode.

creating a large files during checkpoint disable until it runs out of

space and then delete it, then remount to enable checkpoint again, and

then unmount the filesystem triggers the f2fs_bug_on as below:

------------[ cut here ]------------

kernel BUG at fs/f2fs/inode.c:896!

CPU: 2 UID: 0 PID: 1286 Comm: umount Not tainted 6.11.0-rc7-dirty #360

Oops: invalid opcode: 0000 [#1] PREEMPT SMP NOPTI

RIP: 0010:f2fs_evict_inode+0x58c/0x610

Call Trace:

__die_body+0x15/0x60

die+0x33/0x50

do_trap+0x10a/0x120

f2fs_evict_inode+0x58c/0x610

do_error_trap+0x60/0x80

f2fs_evict_inode+0x58c/0x610

exc_invalid_op+0x53/0x60

f2fs_evict_inode+0x58c/0x610

asm_exc_invalid_op+0x16/0x20

f2fs_evict_inode+0x58c/0x610

evict+0x101/0x260

dispose_list+0x30/0x50

evict_inodes+0x140/0x190

generic_shutdown_super+0x2f/0x150

kill_block_super+0x11/0x40

kill_f2fs_super+0x7d/0x140

deactivate_locked_super+0x2a/0x70

cleanup_mnt+0xb3/0x140

task_work_run+0x61/0x90

The root cause is: creating large files during disable checkpoint

period results in not enough free segments, so when writing back root

inode will failed in f2fs_enable_checkpoint. When umount the file

system after enabling checkpoint, the root inode is dirty in

f2fs_evict_inode function, which triggers BUG_ON. The steps to

reproduce are as follows:

dd if=/dev/zero of=f2fs.img bs=1M count=55

mount f2fs.img f2fs_dir -o checkpoint=disable:10%

dd if=/dev/zero of=big bs=1M count=50

sync

rm big

mount -o remount,checkpoint=enable f2fs_dir

umount f2fs_dir

Let's redirty inode when there is not free segments during checkpoint

is disable.