P1        P2        P3
run_gc
 ubifs_garbage_collect
              do_commit
 ubifs_return_leb
  ubifs_lpt_lookup_dirty
   dirty_cow_nnode
                       do_commit
			nothing_to_commit
			 if (test_bit(DIRTY_CNODE, &c->nroot->flags)
			 // false
   test_and_set_bit(DIRTY_CNODE, &nnode->flags)
   c->dirty_nn_cnt += 1
                         ubifs_assert(c, c->dirty_nn_cnt == 0)
			 // false !

[   51.573662] COMMIT
[   51.671867] COMMIT
[   51.778638] Wait sync commit1 twice
[   51.830773] COMMIT
[   51.854184] COMMIT
[   51.888462] wait done
[   51.893241] wait sync commit2
[   51.904395] COMMIT
[   51.904819] sync dirty
[   52.093823] wait2 done
[   52.094280] Add dirty A
[   52.102687] Add dirty A
[   52.111500] sync done
[   52.112023] UBIFS error (ubi0:0 pid 6641): ubifs_assert_failed [ubifs]: UBIFS assert failed: c->dirty_pn_cnt == 0, in fs/ubifs/commit.c:97
[   52.114861] UBIFS warning (ubi0:0 pid 6641): ubifs_ro_mode [ubifs]: switched to read-only mode, error -22
[   52.116767] CPU: 3 PID: 6641 Comm: sync Not tainted 5.10.0-00050-g844b9b09b393-dirty #197
[   52.118150] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014
[   52.120349] Call Trace:
[   52.120818]  dump_stack+0xa6/0xd5
[   52.121390]  ubifs_ro_mode+0x54/0x60 [ubifs]
[   52.122131]  ubifs_assert_failed+0x4b/0x80 [ubifs]
[   52.122950]  do_commit.cold+0x2af/0x7e3 [ubifs]
[   52.123747]  ? sync_inodes_sb+0x27c/0x420
[   52.124409]  ? hrtimer_try_to_cancel+0x20/0x170
[   52.125239]  ubifs_run_commit+0xd5/0x1d0 [ubifs]
[   52.126059]  ubifs_sync_fs+0xca/0x110 [ubifs]
[   52.126808]  sync_filesystem+0xb2/0x130
[   52.127491]  __se_sys_syncfs+0x56/0xf0
[   52.128114]  __x64_sys_syncfs+0x16/0x20
[   52.128761]  do_syscall_64+0x57/0xc0
[   52.129359]  entry_SYSCALL_64_after_hwframe+0x61/0xc6
[   52.130326] RIP: 0033:0x7fa068faef27