Summary

WT_CONN_RECONFIGURING_STEP_UP is stored in conn->flags_atomic, which is managed with F_SET_ATOMIC_32 / F_CLR_ATOMIC_32. However, __disagg_step_up sets and clears the flag using the non-atomic F_SET / F_CLR, and the reader in __wt_evict_needed uses the non-atomic F_ISSET. Without atomic semantics this is a TSAN-visible data race that can cause the eviction heuristic to miss the step-up state on weakly-ordered architectures.

Impact

TSAN-visible data race. Disaggregated storage only.

Files

• src/conn/conn_layered.c
• src/evict/evict_inline.h

Fix

// src/conn/conn_layered.c
-F_SET(conn, WT_CONN_RECONFIGURING_STEP_UP);
+F_SET_ATOMIC_32(conn, WT_CONN_RECONFIGURING_STEP_UP);
-F_CLR(conn, WT_CONN_RECONFIGURING_STEP_UP);
+F_CLR_ATOMIC_32(conn, WT_CONN_RECONFIGURING_STEP_UP);

// src/evict/evict_inline.h
-F_ISSET(conn, WT_CONN_RECONFIGURING_STEP_UP)
+F_ISSET_ATOMIC_32(conn, WT_CONN_RECONFIGURING_STEP_UP)

Notes

Discovered during development on the WT-16973 clean-scrub eviction branch (PR #13605). Disagg only. Fix is independent of that feature and should be applied directly to develop.