From 971eba81ac3b150f806f5414e10ae4808ebf92ad Mon Sep 17 00:00:00 2001
From: Rodrigo Kumpera <kumpera@gmail.com>
Date: Fri, 6 Dec 2013 15:23:02 -0500
Subject: [PATCH] [sgen]Fix a deadlock when the GC try to free a JI during
 world restart. Fixes #15759

This is deadlock prone as the GC lock is a leaf lock while the domain
lock required to free a JI is not.

There are plenty of places where we alloc memory while holding the
domain lock, so we cannot do it the other way.
---
 mono/metadata/sgen-gc.c  | 8 +++++++-
 mono/metadata/sgen-gc.h  | 6 ++----
 mono/metadata/sgen-stw.c | 2 +-
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/mono/metadata/sgen-gc.c b/mono/metadata/sgen-gc.c
index 0c0b15b75da..95f263c1c59 100644
--- a/mono/metadata/sgen-gc.c
+++ b/mono/metadata/sgen-gc.c
@@ -401,6 +401,7 @@ sgen_safe_name (void* obj)
  * ######################################################################
  */
 LOCK_DECLARE (gc_mutex);
+gboolean sgen_try_free_some_memory;
 
 #define SCAN_START_SIZE	SGEN_SCAN_START_SIZE
 
@@ -5597,7 +5598,12 @@ sgen_gc_lock (void)
 void
 sgen_gc_unlock (void)
 {
-	UNLOCK_GC;
+	gboolean try_free = sgen_try_free_some_memory;
+	sgen_try_free_some_memory = FALSE;
+	mono_mutex_unlock (&gc_mutex);
+	MONO_GC_UNLOCKED ();
+	if (try_free)
+		mono_thread_hazardous_try_free_some ();
 }
 
 void
diff --git a/mono/metadata/sgen-gc.h b/mono/metadata/sgen-gc.h
index 9f5902ea268..15afdbcd03a 100644
--- a/mono/metadata/sgen-gc.h
+++ b/mono/metadata/sgen-gc.h
@@ -158,10 +158,7 @@ struct _GCMemSection {
 		MONO_GC_LOCKED ();				\
 	} while (0)
 #define TRYLOCK_GC (mono_mutex_trylock (&gc_mutex) == 0)
-#define UNLOCK_GC do {						\
-		mono_mutex_unlock (&gc_mutex);			\
-		MONO_GC_UNLOCKED ();				\
-	} while (0)
+#define UNLOCK_GC do { sgen_gc_unlock (); } while (0)
 
 extern LOCK_DECLARE (sgen_interruption_mutex);
 
@@ -979,6 +976,7 @@ extern int degraded_mode;
 extern int default_nursery_size;
 extern guint32 tlab_size;
 extern NurseryClearPolicy nursery_clear_policy;
+extern gboolean sgen_try_free_some_memory;
 
 extern LOCK_DECLARE (gc_mutex);
 
diff --git a/mono/metadata/sgen-stw.c b/mono/metadata/sgen-stw.c
index 0f52505544c..54dc218b584 100755
--- a/mono/metadata/sgen-stw.c
+++ b/mono/metadata/sgen-stw.c
@@ -277,7 +277,7 @@ sgen_restart_world (int generation, GGTimingInfo *timing)
 	 */
 	release_gc_locks ();
 
-	mono_thread_hazardous_try_free_some ();
+	sgen_try_free_some_memory = TRUE;
 
 	sgen_bridge_processing_finish (generation);
 
-- 
2.25.1