erofs: kill hooked chains to avoid loops on deduplicated compressed images

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

erofs: kill hooked chains to avoid loops on deduplicated compressed images

After heavily stressing EROFS with several images which include a

hand-crafted image of repeated patterns for more than 46 days, I found

two chains could be linked with each other almost simultaneously and

form a loop so that the entire loop won't be submitted. As a

consequence, the corresponding file pages will remain locked forever.

It can be _only_ observed on data-deduplicated compressed images.

For example, consider two chains with five pclusters in total:

Chain 1: 2->3->4->5 -- The tail pcluster is 5;

Chain 2: 5->1->2 -- The tail pcluster is 2.

Chain 2 could link to Chain 1 with pcluster 5; and Chain 1 could link

to Chain 2 at the same time with pcluster 2.

Since hooked chains are all linked locklessly now, I have no idea how

to simply avoid the race. Instead, let's avoid hooked chains completely

until I could work out a proper way to fix this and end users finally

tell us that it's needed to add it back.

Actually, this optimization can be found with multi-threaded workloads

(especially even more often on deduplicated compressed images), yet I'm

not sure about the overall system impacts of not having this compared

with implementation complexity.