ubifs: Fix deadlock in concurrent rename whiteout and inode writeback

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

ubifs: Fix deadlock in concurrent rename whiteout and inode writeback

Following hung tasks:

[ 77.028764] task:kworker/u8:4 state:D stack: 0 pid: 132

[ 77.028820] Call Trace:

[ 77.029027] schedule+0x8c/0x1b0

[ 77.029067] mutex_lock+0x50/0x60

[ 77.029074] ubifs_write_inode+0x68/0x1f0 [ubifs]

[ 77.029117] __writeback_single_inode+0x43c/0x570

[ 77.029128] writeback_sb_inodes+0x259/0x740

[ 77.029148] wb_writeback+0x107/0x4d0

[ 77.029163] wb_workfn+0x162/0x7b0

[ 92.390442] task:aa state:D stack: 0 pid: 1506

[ 92.390448] Call Trace:

[ 92.390458] schedule+0x8c/0x1b0

[ 92.390461] wb_wait_for_completion+0x82/0xd0

[ 92.390469] __writeback_inodes_sb_nr+0xb2/0x110

[ 92.390472] writeback_inodes_sb_nr+0x14/0x20

[ 92.390476] ubifs_budget_space+0x705/0xdd0 [ubifs]

[ 92.390503] do_rename.cold+0x7f/0x187 [ubifs]

[ 92.390549] ubifs_rename+0x8b/0x180 [ubifs]

[ 92.390571] vfs_rename+0xdb2/0x1170

[ 92.390580] do_renameat2+0x554/0x770

, are caused by concurrent rename whiteout and inode writeback processes:

rename_whiteout(Thread 1) wb_workfn(Thread2)

ubifs_rename

do_rename

lock_4_inodes (Hold ui_mutex)

ubifs_budget_space

make_free_space

shrink_liability

__writeback_inodes_sb_nr

bdi_split_work_to_wbs (Queue new wb work)

wb_do_writeback(wb work)

__writeback_single_inode

ubifs_write_inode

LOCK(ui_mutex)

↑

wb_wait_for_completion (Wait wb work) <-- deadlock!

Reproducer (Detail program in [Link]):

1. SYS_renameat2("/mp/dir/file", "/mp/dir/whiteout", RENAME_WHITEOUT)

2. Consume out of space before kernel(mdelay) doing budget for whiteout

Fix it by doing whiteout space budget before locking ubifs inodes.

BTW, it also fixes wrong goto tag 'out_release' in whiteout budget

error handling path(It should at least recover dir i_size and unlock

4 ubifs inodes).