The instruction selector can deadlock during compilation if method A
invokes method B and the same method B also invokes method A. Fix that
by using pthread_mutex_trylock() and treating the target method as not
compiled of the mutex is under contention.
Fixes the following deadlock found by helgrind:
==5206== Thread #1: lock order "0x4A4C0CC before 0x18A9F5A4" violated
==5206== at 0x40264B7: pthread_mutex_lock (hg_intercepts.c:408)
==5206== by 0x805ED27: mono_burg_emit (insn-selector.c:730)
==5206== by 0x80608F3: emit_code (insn-selector.c:874)
==5206== by 0x8060A57: select_instructions (insn-selector.c:925)
==5206== by 0x80652B6: compile (compiler.c:80)
==5206== by 0x806C4C9: jit_magic_trampoline (trampoline.c:97)
==5206== by 0x890640C: ???
==5206== by 0x89069A3: ???
==5206== by 0x4DAE7FF: ???
==5206== by 0x4DAE7FF: ???
Cc: Tomek Grabiec <tgrab...@gmail.com>
Signed-off-by: Pekka Enberg <penb...@cs.helsinki.fi>
---
arch/x86/insn-selector.brg | 22 ++++++++++++----------
1 files changed, 12 insertions(+), 10 deletions(-)
diff --git a/arch/x86/insn-selector.brg b/arch/x86/insn-selector.brg
index c2d06c3..26bcfd5 100644
--- a/arch/x86/insn-selector.brg
+++ b/arch/x86/insn-selector.brg
@@ -3170,25 +3170,27 @@ static void invoke(struct basic_block *s, struct
tree_node *tree)
{
struct compilation_unit *cu;
struct vm_method *method;
+ bool is_compiled = false;
struct statement *stmt;
struct insn *call_insn;
int nr_stack_args;
- bool is_compiled;
void *target;
stmt = to_stmt(tree);
method = stmt->target_method;
cu = method->compilation_unit;
- if (cu == s->b_parent) {
- /*
- * This is recursive invocation so we call the trampoline.
- */
- is_compiled = false;
- target = vm_method_trampoline_ptr(method);
- } else {
- pthread_mutex_lock(&cu->mutex);
+ is_compiled = false;
+ target = vm_method_trampoline_ptr(method);
+ /*
+ * Look out for an ABBA deadlock during compilation if a method
+ * A invokes method B and the same method B invokes method A as
+ * well. Therefore, if cu->mutex is under contention, treat the
+ * target method as not compiled and let trampoline
+ * backpatching deal with it later.
+ */
+ if (pthread_mutex_trylock(&cu->mutex) == 0) {
is_compiled = cu->is_compiled;
if (is_compiled)
target = vm_method_native_ptr(method);
--
1.5.6.3
------------------------------------------------------------------------------
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