From e96c44e32d0b95eecdff9db344617fd24027eeba Mon Sep 17 00:00:00 2001
From: Maria Matejka <mq@ucw.cz>
Date: Thu, 27 Jun 2024 09:08:01 +0200
Subject: [PATCH] fixup! Forbid locking altogether when RCU reader is active

---
 sysdep/unix/alloc.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/sysdep/unix/alloc.c b/sysdep/unix/alloc.c
index 1cf41a5b..0432b9e2 100644
--- a/sysdep/unix/alloc.c
+++ b/sysdep/unix/alloc.c
@@ -215,6 +215,14 @@ alloc_page(void)
   /* Reinstate the stack with zero */
   PAGE_STACK_PUT(NULL);
 
+  if (rcu_read_active())
+  {
+    /* We can't lock and we actually shouldn't alloc either when rcu is active
+     * but that's a quest for another day. */
+  }
+  else
+  {
+
   /* If there is any free page kept cold, we use that. */
   LOCK_DOMAIN(resource, empty_pages_domain);
   if (empty_pages) {
@@ -244,6 +252,8 @@ alloc_page(void)
   if (fp)
     return fp;
 
+  }
+
   /* And in the worst case, allocate some new pages by mmap() */
   void *ptr = alloc_sys_page();
   ajlog(ptr, NULL, 0, AJT_ALLOC_MMAP);