From 066980729c57e00abc3765053cf3f39e3d223a54 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Fri, 3 Nov 2023 08:05:46 +0200
Subject: Fix data race in match options logic

---
 libbuild2/algorithm.cxx | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

(limited to 'libbuild2/algorithm.cxx')

diff --git a/libbuild2/algorithm.cxx b/libbuild2/algorithm.cxx
index 1f2d88b..0e995d5 100644
--- a/libbuild2/algorithm.cxx
+++ b/libbuild2/algorithm.cxx
@@ -291,7 +291,12 @@ namespace build2
       // We don't lock already applied or executed targets unless there
       // are new options.
       //
-      if (e >= appl && (cs.match_extra.cur_options & options) == options)
+      // Note: we don't have the lock yet so we must use atomic cur_options.
+      // We also have to re-check this once we've grabbed the lock.
+      //
+      if (e >= appl &&
+          (cs.match_extra.cur_options_.load (memory_order_relaxed) & options)
+          == options)
         return target_lock {a, nullptr, e - b, false};
     }
 
@@ -312,7 +317,21 @@ namespace build2
       offset = target::offset_touched;
     }
     else
+    {
+      // Re-check the options if already applied or worse.
+      //
+      if (e >= appl && (s.match_extra.cur_options & options) == options)
+      {
+        // Essentially unlock_impl().
+        //
+        task_count.store (e, memory_order_release);
+        ctx.sched->resume (task_count);
+
+        return target_lock {a, nullptr, e - b, false};
+      }
+
       offset = e - b;
+    }
 
     return target_lock {a, &t, offset, first};
   }
@@ -962,6 +981,7 @@ namespace build2
     recipe re (ar != nullptr ? f (*ar, a, t, me) : ru.apply (a, t, me));
 
     me.free (); // Note: cur_options are still in use.
+    me.cur_options_.store (me.cur_options, memory_order_relaxed);
     return re;
   }
 
@@ -1024,6 +1044,7 @@ namespace build2
     // Note: for now no adhoc_reapply().
     //
     ru.reapply (a, t, me);
+    me.cur_options_.store (me.cur_options, memory_order_relaxed);
   }
 
   // If anything goes wrong, set target state to failed and return nullopt.
-- 
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