[LU-11568] Get rid of SLAB_DESTROY_BY_RCU

• Type: Bug
• Resolution: Fixed
• Priority: Critical
• Fix Version/s: Lustre 2.13.0, Lustre 2.12.1
• Affects Version/s: Lustre 2.13.0
• Severity: 3
• Assignee: Oleg Drokin
• Reporter: Oleg Drokin

Description

This code was introduced by bz 18015 https://bugzilla.lustre.org/show_bug.cgi?id=18015

Newer kernels rename that symbol and it's not used anyway, but also at least in RHEL 7.[345] there's bug in this functionality htat leads to use after frees that are seen prominently in our nfs testing in maloo (in addition to my testrig). See LU-11063.
Example nfs failures:
https://testing.whamcloud.com/test_sessions/1cd5592c-8319-4aa7-aa2b-4549a83ce9cd
https://testing.whamcloud.com/test_sessions/9e6c8dec-d1dd-4ad4-b028-f98b5fdf63a9

Anyway after reviewing the original patch I think we just need to get rid of this flag altogether and if the rapid load/unload is still a problem, work it around in some better more robust way.

Issue Links

• is related to: LU-11063 RHEL7.[345] RCU breakage