kern_copy_file_range(): handle rangelock recursion

[kib]

Test Plan

How exactly to run the fusefs tests?

[kib]

Re-check that we are still in cheating mode after CAS failure to set DRAINING.

[lwhsu]

The fusefs tests are still failing with this change. :-(

To run fusefs tests:

kldload fusefs.ko
cd /usr/tests/sys/fs/fusefs

then

kyua test

or execute each group directly:

./copy_file_range

Source codes are at src/tests/sys/fs/fusefs.

[kib]

Actually switch to non-cheating mode in rangelock_may_recurse().

With this update, copy_file_range() test does not hang for me. OTOH, I see write test timing out, but no hanging or unkillable processes are left. It might be due to my machine having real hw serial console which is slow, and fusefs tests are quite chatty.

Could you please confirm whether updated patch works for you?

[lwhsu]

I have tested it and all the fusefs tests are passed. Thanks very much!

[markj]

sys/kern/kern_rangelock.c

92

The cast is not needed (anymore).

788

Why do these operations need release semantics?

[kib]

Remove _rel modifier.
Remove unneeded casts.

[markj]

sys/kern/kern_rangelock.c

783

Should we restart this loop if the cmpset fails?

[kib]

Fix draining case when CAS failed.

[lwhsu]

I have tested again with the latest patch and all the tests passed.