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authorSverker Eriksson <[email protected]>2017-01-12 13:58:26 +0100
committerSverker Eriksson <[email protected]>2017-01-12 13:58:26 +0100
commitaf5169d85fcd545e3c857a219db081a62f33404d (patch)
treea08ad74d060311ada3b11b76fd419a1d01e32415 /erts
parent2b41d8f318b7e5ec139d42fd2f01a132699be839 (diff)
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erts: Fix race bug between export fun creation and code loading
Symptom: SEGV crash on ARM in delete_code() -> export_list(). Could probably happen on other machines as well. Problem: Staging export table was iterated in an unsafe way while an entry was added for a new export fun. Solution: Correct write order and some memory barriers.
Diffstat (limited to 'erts')
-rw-r--r--erts/emulator/beam/beam_bif_load.c14
-rw-r--r--erts/emulator/beam/beam_load.c11
-rw-r--r--erts/emulator/beam/export.c2
-rw-r--r--erts/emulator/beam/index.c9
-rw-r--r--erts/emulator/beam/index.h14
5 files changed, 37 insertions, 13 deletions
diff --git a/erts/emulator/beam/beam_bif_load.c b/erts/emulator/beam/beam_bif_load.c
index 5969197168..93f5ed500b 100644
--- a/erts/emulator/beam/beam_bif_load.c
+++ b/erts/emulator/beam/beam_bif_load.c
@@ -786,7 +786,7 @@ BIF_RETTYPE finish_after_on_load_2(BIF_ALIST_2)
}
if (BIF_ARG_2 == am_true) {
- int i;
+ int i, num_exps;
/*
* Make the code with the on_load function current.
@@ -802,7 +802,8 @@ BIF_RETTYPE finish_after_on_load_2(BIF_ALIST_2)
/*
* The on_load function succeded. Fix up export entries.
*/
- for (i = 0; i < export_list_size(code_ix); i++) {
+ num_exps = export_list_size(code_ix);
+ for (i = 0; i < num_exps; i++) {
Export *ep = export_list(i,code_ix);
if (ep == NULL || ep->code[0] != BIF_ARG_1) {
continue;
@@ -822,14 +823,15 @@ BIF_RETTYPE finish_after_on_load_2(BIF_ALIST_2)
modp->curr.code_hdr->on_load_function_ptr = NULL;
set_default_trace_pattern(BIF_ARG_1);
} else if (BIF_ARG_2 == am_false) {
- int i;
+ int i, num_exps;
/*
* The on_load function failed. Remove references to the
* code that is about to be purged from the export entries.
*/
- for (i = 0; i < export_list_size(code_ix); i++) {
+ num_exps = export_list_size(code_ix);
+ for (i = 0; i < num_exps; i++) {
Export *ep = export_list(i,code_ix);
if (ep == NULL || ep->code[0] != BIF_ARG_1) {
continue;
@@ -2011,9 +2013,9 @@ delete_code(Module* modp)
{
ErtsCodeIndex code_ix = erts_staging_code_ix();
Eterm module = make_atom(modp->module);
- int i;
+ int i, num_exps = export_list_size(code_ix);
- for (i = 0; i < export_list_size(code_ix); i++) {
+ for (i = 0; i < num_exps; i++) {
Export *ep = export_list(i, code_ix);
if (ep != NULL && (ep->code[0] == module)) {
if (ep->addressv[code_ix] == ep->code+3) {
diff --git a/erts/emulator/beam/beam_load.c b/erts/emulator/beam/beam_load.c
index 0afdedf6c2..3f2bdf3f9d 100644
--- a/erts/emulator/beam/beam_load.c
+++ b/erts/emulator/beam/beam_load.c
@@ -797,14 +797,14 @@ erts_finish_loading(Binary* magic, Process* c_p,
} else {
ErtsCodeIndex code_ix = erts_staging_code_ix();
Eterm module = stp->module;
- int i;
+ int i, num_exps;
/*
* There is an -on_load() function. We will keep the current
* code, but we must turn off any tracing.
*/
-
- for (i = 0; i < export_list_size(code_ix); i++) {
+ num_exps = export_list_size(code_ix);
+ for (i = 0; i < num_exps; i++) {
Export *ep = export_list(i, code_ix);
if (ep == NULL || ep->code[0] != module) {
continue;
@@ -5754,12 +5754,13 @@ exported_from_module(Process* p, /* Process whose heap to use. */
ErtsCodeIndex code_ix,
Eterm mod) /* Tagged atom for module. */
{
- int i;
+ int i, num_exps;
Eterm* hp = NULL;
Eterm* hend = NULL;
Eterm result = NIL;
- for (i = 0; i < export_list_size(code_ix); i++) {
+ num_exps = export_list_size(code_ix);
+ for (i = 0; i < num_exps; i++) {
Export* ep = export_list(i,code_ix);
if (ep->code[0] == mod) {
diff --git a/erts/emulator/beam/export.c b/erts/emulator/beam/export.c
index 2a19211987..2a007ce860 100644
--- a/erts/emulator/beam/export.c
+++ b/erts/emulator/beam/export.c
@@ -348,7 +348,7 @@ Export *export_list(int i, ErtsCodeIndex code_ix)
int export_list_size(ErtsCodeIndex code_ix)
{
- return export_tables[code_ix].entries;
+ return erts_index_num_entries(&export_tables[code_ix]);
}
int export_table_sz(void)
diff --git a/erts/emulator/beam/index.c b/erts/emulator/beam/index.c
index 26d6c04ea0..4cebb4d8fa 100644
--- a/erts/emulator/beam/index.c
+++ b/erts/emulator/beam/index.c
@@ -91,9 +91,16 @@ index_put_entry(IndexTable* t, void* tmpl)
t->seg_table[ix>>INDEX_PAGE_SHIFT] = erts_alloc(t->type, sz);
t->size += INDEX_PAGE_SIZE;
}
- t->entries++;
p->index = ix;
t->seg_table[ix>>INDEX_PAGE_SHIFT][ix&INDEX_PAGE_MASK] = p;
+
+ /*
+ * Do a write barrier here to allow readers to do lock free iteration.
+ * erts_index_num_entries() does matching read barrier.
+ */
+ ERTS_SMP_WRITE_MEMORY_BARRIER;
+ t->entries++;
+
return p;
}
diff --git a/erts/emulator/beam/index.h b/erts/emulator/beam/index.h
index 0a109d8699..532dec0168 100644
--- a/erts/emulator/beam/index.h
+++ b/erts/emulator/beam/index.h
@@ -65,6 +65,7 @@ void index_erase_latest_from(IndexTable*, Uint ix);
ERTS_GLB_INLINE int index_put(IndexTable*, void*);
ERTS_GLB_INLINE IndexSlot* erts_index_lookup(IndexTable*, Uint);
+ERTS_GLB_INLINE int erts_index_num_entries(IndexTable* t);
#if ERTS_GLB_INLINE_INCL_FUNC_DEF
@@ -78,6 +79,19 @@ erts_index_lookup(IndexTable* t, Uint ix)
{
return t->seg_table[ix>>INDEX_PAGE_SHIFT][ix&INDEX_PAGE_MASK];
}
+
+ERTS_GLB_INLINE int erts_index_num_entries(IndexTable* t)
+{
+ int ret = t->entries;
+ /*
+ * Do a read barrier here to allow lock free iteration
+ * on tables where entries are never erased.
+ * index_put_entry() does matching write barrier.
+ */
+ ERTS_SMP_READ_MEMORY_BARRIER;
+ return ret;
+}
+
#endif
#endif