From ee94788e63d9f35daca7c0d1e80a488f738a9c52 Mon Sep 17 00:00:00 2001
From: Thierry Bordaz <tbordaz@redhat.com>
Date: Sep 01 2023 09:02:08 +0000
Subject: BZ 2124214 - schema compat plugin deadlock on delete post op


Bug description:
	backends locks (SC map and retroCL) are acquired in
	the opposite order
	(https://bugzilla.redhat.com/show_bug.cgi?id=2124214#c17)

Fix description:
	Credits of the fix are to Pierre Rogier who found
	a reproducible testcase, did the fix and verified it.

	In specific condition of retroCL trimming the DEL
	callback of the SC should check if the backend should
	be ignored

relates: 2124214

---

diff --git a/src/back-shr.c b/src/back-shr.c
index ce2b1f3..1792bef 100644
--- a/src/back-shr.c
+++ b/src/back-shr.c
@@ -2811,6 +2811,18 @@ backend_shr_delete_cb(Slapi_PBlock *pb)
 	if (wrap_get_call_level() > 0) {
 		return 0;
 	}
+        /* especially important to test if we want to prevent frequent
+         * deadlocks when backends are accesses in opposite order.
+         * i.e. "regular" update on domain map+retroCL and retroCL trimming
+         * retroCL+domain map
+         */
+        if (backend_shr_write_ignore(pb)) {
+#if DEBUG_MAP_LOCK
+        slapi_log_error(SLAPI_LOG_FATAL, "schema-compat",
+                "backend_shr_delete_cb: (%p) operation is not impacting schema compat\n", PR_MyThreadId(), 1);
+#endif
+		return 0;
+	}
 
 	/* Read parameters from the pblock. */
 	slapi_pblock_get(pb, SLAPI_PLUGIN_PRIVATE, &cbdata.state);