dm-raid456, md/raid456: fix a deadlock for dm-raid456 while io concurrent with reshape

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

dm-raid456, md/raid456: fix a deadlock for dm-raid456 while io concurrent with reshape

For raid456, if reshape is still in progress, then IO across reshape

position will wait for reshape to make progress. However, for dm-raid,

in following cases reshape will never make progress hence IO will hang:

1) the array is read-only;

2) MD_RECOVERY_WAIT is set;

3) MD_RECOVERY_FROZEN is set;

After commit c467e97f079f ("md/raid6: use valid sector values to determine

if an I/O should wait on the reshape") fix the problem that IO across

reshape position doesn't wait for reshape, the dm-raid test

shell/lvconvert-raid-reshape.sh start to hang:

[root@fedora ~]# cat /proc/979/stack

[<0>] wait_woken+0x7d/0x90

[<0>] raid5_make_request+0x929/0x1d70 [raid456]

[<0>] md_handle_request+0xc2/0x3b0 [md_mod]

[<0>] raid_map+0x2c/0x50 [dm_raid]

[<0>] __map_bio+0x251/0x380 [dm_mod]

[<0>] dm_submit_bio+0x1f0/0x760 [dm_mod]

[<0>] __submit_bio+0xc2/0x1c0

[<0>] submit_bio_noacct_nocheck+0x17f/0x450

[<0>] submit_bio_noacct+0x2bc/0x780

[<0>] submit_bio+0x70/0xc0

[<0>] mpage_readahead+0x169/0x1f0

[<0>] blkdev_readahead+0x18/0x30

[<0>] read_pages+0x7c/0x3b0

[<0>] page_cache_ra_unbounded+0x1ab/0x280

[<0>] force_page_cache_ra+0x9e/0x130

[<0>] page_cache_sync_ra+0x3b/0x110

[<0>] filemap_get_pages+0x143/0xa30

[<0>] filemap_read+0xdc/0x4b0

[<0>] blkdev_read_iter+0x75/0x200

[<0>] vfs_read+0x272/0x460

[<0>] ksys_read+0x7a/0x170

[<0>] __x64_sys_read+0x1c/0x30

[<0>] do_syscall_64+0xc6/0x230

[<0>] entry_SYSCALL_64_after_hwframe+0x6c/0x74

This is because reshape can't make progress.

For md/raid, the problem doesn't exist because register new sync_thread

doesn't rely on the IO to be done any more:

1) If array is read-only, it can switch to read-write by ioctl/sysfs;

2) md/raid never set MD_RECOVERY_WAIT;

3) If MD_RECOVERY_FROZEN is set, mddev_suspend() doesn't hold

'reconfig_mutex', hence it can be cleared and reshape can continue by

sysfs api 'sync_action'.

However, I'm not sure yet how to avoid the problem in dm-raid yet. This

patch on the one hand make sure raid_message() can't change

sync_thread() through raid_message() after presuspend(), on the other

hand detect the above 3 cases before wait for IO do be done in

dm_suspend(), and let dm-raid requeue those IO.