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

Duplicate — Wed, 8 Mar 2023 01:45:22 +0000

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.

Whamcloud Community JIRA

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