staging: erofs: fix use-after-free of on-stack `z_erofs_vle_unzip_io'

The root cause is the race as follows:
 Thread #0                         Thread #1

 z_erofs_vle_unzip_kickoff         z_erofs_submit_and_unzip

                                    struct z_erofs_vle_unzip_io io[]
   atomic_add_return()
                                    wait_event()
                                    [end of function]
   wake_up()

Fix it by taking the waitqueue lock between atomic_add_return and
wake_up to close such the race.

kernel message:

Unable to handle kernel paging request at virtual address 97f7052caa1303dc
...
Workqueue: kverityd verity_work
task: ffffffe32bcb8000 task.stack: ffffffe3298a0000
PC is at __wake_up_common+0x48/0xa8
LR is at __wake_up+0x3c/0x58
...
Call trace:
...
[<ffffff94a08ff648>] __wake_up_common+0x48/0xa8
[<ffffff94a08ff8b8>] __wake_up+0x3c/0x58
[<ffffff94a0c11b60>] z_erofs_vle_unzip_kickoff+0x40/0x64
[<ffffff94a0c118e4>] z_erofs_vle_read_endio+0x94/0x134
[<ffffff94a0c83c9c>] bio_endio+0xe4/0xf8
[<ffffff94a1076540>] dec_pending+0x134/0x32c
[<ffffff94a1076f28>] clone_endio+0x90/0xf4
[<ffffff94a0c83c9c>] bio_endio+0xe4/0xf8
[<ffffff94a1095024>] verity_work+0x210/0x368
[<ffffff94a08c4150>] process_one_work+0x188/0x4b4
[<ffffff94a08c45bc>] worker_thread+0x140/0x458
[<ffffff94a08cad48>] kthread+0xec/0x108
[<ffffff94a0883ab4>] ret_from_fork+0x10/0x1c
Code: d1006273 54000260 f9400804 b9400019 (b85fc081)
---[ end trace be9dde154f677cd1 ]---
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/erofs/unzip_vle.c

@@ -744,13 +744,18 @@ static void z_erofs_vle_unzip_kickoff(void *ptr, int bios)
 	struct z_erofs_vle_unzip_io *io = tagptr_unfold_ptr(t);
 	bool background = tagptr_unfold_tags(t);
 
-	if (atomic_add_return(bios, &io->pending_bios))
+	if (!background) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&io->u.wait.lock, flags);
+		if (!atomic_add_return(bios, &io->pending_bios))
+			wake_up_locked(&io->u.wait);
+		spin_unlock_irqrestore(&io->u.wait.lock, flags);
 		return;
+	}
 
-	if (background)
+	if (!atomic_add_return(bios, &io->pending_bios))
 		queue_work(z_erofs_workqueue, &io->u.work);
-	else
-		wake_up(&io->u.wait);
 }
 
 static inline void z_erofs_vle_read_endio(struct bio *bio)