From b0d6bf2a34d5e2e0cfb2410f58e768935d527be0 Mon Sep 17 00:00:00 2001
From: Ben Gamari <ben@smart-cactus.org>
Date: Tue, 18 Jun 2019 12:07:50 -0400
Subject: [PATCH] rts: Reset STATIC_LINK field of reverted CAFs
When we revert a CAF we must reset the STATIC_LINK field lest the GC
might ignore the CAF (e.g. as it carries the STATIC_FLAG_LIST flag) and
will consequently overlook references to object code that we are trying
to unload. This would result in the reachable object code being
unloaded. See Note [CAF lists] and Note [STATIC_LINK fields].
This fixes #16842.
Idea-due-to: Phuong Trinh <lolotp@fb.com>
---
rts/sm/GCAux.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/rts/sm/GCAux.c b/rts/sm/GCAux.c
index 23ed3f0622f7..e8ca0c4002a0 100644
--- a/rts/sm/GCAux.c
+++ b/rts/sm/GCAux.c
@@ -114,16 +114,21 @@ isAlive(StgClosure *p)
void
revertCAFs( void )
{
- StgIndStatic *c;
+ StgIndStatic *c = revertible_caf_list;
- for (c = revertible_caf_list;
- c != (StgIndStatic *)END_OF_CAF_LIST;
- c = (StgIndStatic *)c->static_link)
- {
+ while (c != (StgIndStatic *) END_OF_CAF_LIST) {
c = (StgIndStatic *)UNTAG_STATIC_LIST_PTR(c);
+ StgIndStatic *next = (StgIndStatic *) c->static_link;
+
SET_INFO((StgClosure *)c, c->saved_info);
c->saved_info = NULL;
- // could, but not necessary: c->static_link = NULL;
+ // We must reset static_link lest the major GC finds that
+ // static_flag==3 and will consequently ignore references
+ // into code that we are trying to unload. This would result
+ // in reachable object code being unloaded prematurely.
+ // See #16842.
+ c->static_link = NULL;
+ c = next;
}
revertible_caf_list = (StgIndStatic*)END_OF_CAF_LIST;
}
--
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