File 1072-erl_gc-fix-dynamic-tracepoint-for-heap_grow.patch of Package erlang

From 562cd9992cd090ff837c79391ec2e5d89219ddf0 Mon Sep 17 00:00:00 2001
From: Maxim Fedorov <dane@whatsapp.com>
Date: Tue, 15 Dec 2020 11:10:31 -0800
Subject: [PATCH] erl_gc: fix dynamic tracepoint for heap_grow

If stack top is changed before calling heap_grow tracepoint,
the stack is not walk-able, because stack bottom points to
old heap, while stack top is already reset to new heap.
Move tracepoint after all heap references have been updated.
Fix warning when compiling with dtrace enabled.
---
 erts/emulator/beam/erl_gc.c | 51 ++++++++++++++++++++++---------------
 1 file changed, 30 insertions(+), 21 deletions(-)

diff --git a/erts/emulator/beam/erl_gc.c b/erts/emulator/beam/erl_gc.c
index 61b4b81668..b74eaccea8 100644
--- a/erts/emulator/beam/erl_gc.c
+++ b/erts/emulator/beam/erl_gc.c
@@ -697,10 +697,10 @@ garbage_collect(Process* p, ErlHeapFragment *live_hf_end,
     ErtsMonotonicTime start_time;
     ErtsSchedulerData *esdp;
     erts_aint32_t state;
-    ERTS_MSACC_PUSH_STATE();
 #ifdef USE_VM_PROBES
     DTRACE_CHARBUF(pidbuf, DTRACE_TERM_BUF_SIZE);
 #endif
+    ERTS_MSACC_PUSH_STATE();
 
     ERTS_UNDEF(start_time, 0);
     ERTS_CHK_MBUF_SZ(p);
@@ -1772,15 +1772,6 @@ do_minor(Process *p, ErlHeapFragment *live_hf_end,
     sys_memcpy(n_heap + new_sz - n, p->stop, n * sizeof(Eterm));
     p->stop = n_heap + new_sz - n;
 
-#ifdef USE_VM_PROBES
-    if (HEAP_SIZE(p) != new_sz && DTRACE_ENABLED(process_heap_grow)) {
-        DTRACE_CHARBUF(pidbuf, DTRACE_TERM_BUF_SIZE);
-
-        dtrace_proc_str(p, pidbuf);
-        DTRACE3(process_heap_grow, pidbuf, HEAP_SIZE(p), new_sz);
-    }
-#endif
-
 #ifdef HARDDEBUG
     disallow_heap_frag_ref_in_heap(p, n_heap, n_htop);
 #endif
@@ -1789,8 +1780,19 @@ do_minor(Process *p, ErlHeapFragment *live_hf_end,
 
     HEAP_START(p) = n_heap;
     HEAP_TOP(p) = n_htop;
-    HEAP_SIZE(p) = new_sz;
     HEAP_END(p) = n_heap + new_sz;
+
+#ifdef USE_VM_PROBES
+    if (HEAP_SIZE(p) != new_sz && DTRACE_ENABLED(process_heap_grow)) {
+        DTRACE_CHARBUF(pidbuf, DTRACE_TERM_BUF_SIZE);
+        Uint old_sz = HEAP_SIZE(p);
+
+        HEAP_SIZE(p) = new_sz;
+        dtrace_proc_str(p, pidbuf);
+        DTRACE3(process_heap_grow, pidbuf, old_sz, new_sz);
+    }
+#endif
+    HEAP_SIZE(p) = new_sz;
 }
 
 /*
@@ -1863,15 +1865,6 @@ major_collection(Process* p, ErlHeapFragment *live_hf_end,
     sys_memcpy(n_heap + new_sz - stk_sz, p->stop, stk_sz * sizeof(Eterm));
     p->stop = n_heap + new_sz - stk_sz;
 
-#ifdef USE_VM_PROBES
-    if (HEAP_SIZE(p) != new_sz && DTRACE_ENABLED(process_heap_grow)) {
-        DTRACE_CHARBUF(pidbuf, DTRACE_TERM_BUF_SIZE);
-
-        dtrace_proc_str(p, pidbuf);
-        DTRACE3(process_heap_grow, pidbuf, HEAP_SIZE(p), new_sz);
-    }
-#endif
-
 #ifdef HARDDEBUG
     disallow_heap_frag_ref_in_heap(p, n_heap, n_htop);
 #endif
@@ -1880,8 +1873,24 @@ major_collection(Process* p, ErlHeapFragment *live_hf_end,
 
     HEAP_START(p) = n_heap;
     HEAP_TOP(p) = n_htop;
-    HEAP_SIZE(p) = new_sz;
     HEAP_END(p) = n_heap + new_sz;
+
+#ifdef USE_VM_PROBES
+    /* Fire process_heap_grow tracepoint after all heap references have
+     * been updated. This allows to walk the stack. */
+    if (HEAP_SIZE(p) != new_sz && DTRACE_ENABLED(process_heap_grow)) {
+        DTRACE_CHARBUF(pidbuf, DTRACE_TERM_BUF_SIZE);
+        Uint old_sz = HEAP_SIZE(p);
+
+        /* Update the heap size before firing tracepoint */
+        HEAP_SIZE(p) = new_sz;
+
+        dtrace_proc_str(p, pidbuf);
+        DTRACE3(process_heap_grow, pidbuf, old_sz, new_sz);
+    }
+#endif
+    HEAP_SIZE(p) = new_sz;
+
     GEN_GCS(p) = 0;
 
     HIGH_WATER(p) = HEAP_TOP(p);
-- 
2.26.2