patches/bionic/0001-Actually-restore-pre-P-mutex-behavior.patch

From b3343e687842ad54ca1621f6dcb1d99e6826d65d Mon Sep 17 00:00:00 2001
From: Ethan Chen <intervigil@gmail.com>
Date: Tue, 25 Sep 2018 00:11:05 -0700
Subject: [PATCH 1/2] Actually restore pre-P mutex behavior

Apps built against versions < P may not actually expect the EBUSY return
code, and may crash or otherwise misbehave. Check for target SDK
versions earlier than P when performing the IsMutexDestroyed check so
any invocation of HandleUsingDestroyedMutex is bypassed and pre-P mutex
behavior is restored.

See 9e989f12d1186231d97dac6d038db7955acebdf3 for the change that
introduced this new behavior.

Change-Id: I45f8882c9527c63eed1ef5820a5004b8958d58ea
---
 libc/bionic/pthread_mutex.cpp | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/libc/bionic/pthread_mutex.cpp b/libc/bionic/pthread_mutex.cpp
index bc7bd653f..517e52688 100644
--- a/libc/bionic/pthread_mutex.cpp
+++ b/libc/bionic/pthread_mutex.cpp
@@ -782,17 +782,22 @@ static int MutexLockWithTimeout(pthread_mutex_internal_t* mutex, bool use_realti
 
 }  // namespace NonPI
 
-static inline __always_inline bool IsMutexDestroyed(uint16_t mutex_state) {
-    return mutex_state == 0xffff;
-}
-
 // Inlining this function in pthread_mutex_lock() adds the cost of stack frame instructions on
 // ARM64. So make it noinline.
-static int __attribute__((noinline)) HandleUsingDestroyedMutex(pthread_mutex_t* mutex,
-                                                               const char* function_name) {
+static inline __attribute__((noinline)) bool IsMutexDestroyed(uint16_t mutex_state) {
+    // Checking for mutex destruction is a P-specific behavior. Bypass the
+    // check if the SDK version precedes P, so that no change in behavior
+    // that may cause crashes is introduced.
     if (bionic_get_application_target_sdk_version() >= __ANDROID_API_P__) {
-        __fortify_fatal("%s called on a destroyed mutex (%p)", function_name, mutex);
+        return mutex_state == 0xffff;
+    } else {
+        return false;
     }
+}
+
+static int __always_inline HandleUsingDestroyedMutex(pthread_mutex_t* mutex,
+                                                               const char* function_name) {
+    __fortify_fatal("%s called on a destroyed mutex (%p)", function_name, mutex);
     return EBUSY;
 }
 
-- 
2.21.0