[LU-4725] wrong lock ordering in rename leads to deadlocks

• Type: Bug
• Resolution: Fixed
• Priority: Blocker
• Fix Version/s: Lustre 2.6.0, Lustre 2.5.4
• Affects Version/s: Lustre 2.1.6, Lustre 2.6.0, Lustre 2.5.2, Lustre 2.4.3
• Labels: patch
• Severity: 3
• Assignee: Hongchao Zhang
• Reporter: Vitaly Fertman

Description

the current rename code locks objects in the order: src parent, dst parent, src child, dst child. it may happen that dst is a parent of src, what may lead to deadlock.

example from a core dump:
res1 - dst parent
res2 - dst parent, PDO
res3 - src parent

Thread 1 (T1), rename:
Has RES3 (CW,0x2)
Wants RES1 (CW,0x2)

Thread 2 (T2), getattr:
Has RES1(CR,0x2)
Has RES2(PR,0x2)
Wants RES3(PR,0x2) - blocked by T1

Thread 3 (T3), create or open|create
Has RES1(CW,0x2)
Wants RES2(PW,0x2) - blocked by T2

Thread4 (T4), getattr or similar
Wants RES1(PR,0x2) - blocked by T3

T1 has no conflicts, but is sitting in the waiting queue behind T4, thus not granted.

Issue Links

• duplicates: LU-5178 object leak in mdt_rename_sanity()
• is related to: LU-5514 After upgrade from 1.8.7 to 2.5.2 stack trace cfs_hash_bd_lookup_intent
• is related to: LU-5111 interop 2.5 server and higher version client failure on test suite sanityn test_55a: mv succeeded
• is related to: LU-16589 sanityn test_55d: FAIL: (2) mv succeeded
• is related to: LU-5178 object leak in mdt_rename_sanity()