avoid deadlock if crashing inside profile_wr_lock

Author: vtjnash

src/debuginfo.cpp

@@ -147,8 +147,8 @@ struct unw_table_entry
 template <typename T>
 static void jl_profile_atomic(T f) JL_NOTSAFEPOINT
 {
-    assert(0 == jl_lock_profile_rd_held());
-    jl_lock_profile_wr();
+    int havelock = jl_lock_profile_wr();
+    assert(havelock);
 #ifndef _OS_WINDOWS_
     sigset_t sset;
     sigset_t oset;
@@ -159,7 +159,8 @@ static void jl_profile_atomic(T f) JL_NOTSAFEPOINT
 #ifndef _OS_WINDOWS_
     pthread_sigmask(SIG_SETMASK, &oset, NULL);
 #endif
-    jl_unlock_profile_wr();
+    if (havelock)
+        jl_unlock_profile_wr();
 }
 
 
@@ -475,8 +476,8 @@ static int lookup_pointer(
 
     // DWARFContext/DWARFUnit update some internal tables during these queries, so
     // a lock is needed.
-    assert(0 == jl_lock_profile_rd_held());
-    jl_lock_profile_wr();
+    if (!jl_lock_profile_wr())
+        return lookup_pointer(object::SectionRef(), NULL, frames, pointer, slide, demangle, noInline);
     auto inlineInfo = context->getInliningInfoForAddress(makeAddress(Section, pointer + slide), infoSpec);
     jl_unlock_profile_wr();
 
@@ -501,7 +502,8 @@ static int lookup_pointer(
             info = inlineInfo.getFrame(i);
         }
         else {
-            jl_lock_profile_wr();
+            int havelock = jl_lock_profile_wr();
+            assert(havelock); (void)havelock;
             info = context->getLineInfoForAddress(makeAddress(Section, pointer + slide), infoSpec);
             jl_unlock_profile_wr();
         }
@@ -1209,8 +1211,8 @@ int jl_DI_for_fptr(uint64_t fptr, uint64_t *symsize, int64_t *slide,
         object::SectionRef *Section, llvm::DIContext **context) JL_NOTSAFEPOINT
 {
     int found = 0;
-    assert(0 == jl_lock_profile_rd_held());
-    jl_lock_profile_wr();
+    if (!jl_lock_profile_wr())
+        return 0;
 
     if (symsize)
         *symsize = 0;

src/julia_internal.h

@@ -210,10 +210,9 @@ JL_DLLEXPORT double jl_get_profile_peek_duration(void);
 JL_DLLEXPORT void jl_set_profile_peek_duration(double);
 
 JL_DLLEXPORT void jl_init_profile_lock(void);
-JL_DLLEXPORT uintptr_t jl_lock_profile_rd_held(void) JL_NOTSAFEPOINT;
-JL_DLLEXPORT void jl_lock_profile(void) JL_NOTSAFEPOINT JL_NOTSAFEPOINT_ENTER;
+JL_DLLEXPORT int jl_lock_profile(void) JL_NOTSAFEPOINT JL_NOTSAFEPOINT_ENTER;
 JL_DLLEXPORT void jl_unlock_profile(void) JL_NOTSAFEPOINT JL_NOTSAFEPOINT_LEAVE;
-JL_DLLEXPORT void jl_lock_profile_wr(void) JL_NOTSAFEPOINT JL_NOTSAFEPOINT_ENTER;
+JL_DLLEXPORT int jl_lock_profile_wr(void) JL_NOTSAFEPOINT JL_NOTSAFEPOINT_ENTER;
 JL_DLLEXPORT void jl_unlock_profile_wr(void) JL_NOTSAFEPOINT JL_NOTSAFEPOINT_LEAVE;
 void jl_with_stackwalk_lock(void (*f)(void*) JL_NOTSAFEPOINT, void *ctx) JL_NOTSAFEPOINT;
 

src/signal-handling.c

@@ -102,7 +102,7 @@ void jl_init_profile_lock(void)
 #endif
 }
 
-uintptr_t jl_lock_profile_rd_held(void)
+static uintptr_t jl_lock_profile_rd_held(void)
 {
 #ifndef _OS_WINDOWS_
     return (uintptr_t)pthread_getspecific(debuginfo_asyncsafe_held);
@@ -111,38 +111,69 @@ uintptr_t jl_lock_profile_rd_held(void)
 #endif
 }
 
-void jl_lock_profile(void)
+int jl_lock_profile(void)
 {
     uintptr_t held = jl_lock_profile_rd_held();
-    if (held++ == 0)
+    if (held == -1)
+        return 0;
+    if (held == 0) {
+        held = -1;
+#ifndef _OS_WINDOWS_
+        pthread_setspecific(debuginfo_asyncsafe_held, (void*)held);
+#else
+        TlsSetValue(debuginfo_asyncsafe_held, (void*)held);
+#endif
         uv_rwlock_rdlock(&debuginfo_asyncsafe);
+        held = 0;
+    }
+    held++;
 #ifndef _OS_WINDOWS_
     pthread_setspecific(debuginfo_asyncsafe_held, (void*)held);
 #else
     TlsSetValue(debuginfo_asyncsafe_held, (void*)held);
 #endif
+    return 1;
 }
 
 JL_DLLEXPORT void jl_unlock_profile(void)
 {
     uintptr_t held = jl_lock_profile_rd_held();
-    assert(held);
-    if (--held == 0)
-        uv_rwlock_rdunlock(&debuginfo_asyncsafe);
+    assert(held && held != -1);
+    held--;
 #ifndef _OS_WINDOWS_
     pthread_setspecific(debuginfo_asyncsafe_held, (void*)held);
 #else
     TlsSetValue(debuginfo_asyncsafe_held, (void*)held);
 #endif
+    if (held == 0)
+        uv_rwlock_rdunlock(&debuginfo_asyncsafe);
 }
 
-void jl_lock_profile_wr(void)
+int jl_lock_profile_wr(void)
 {
+    uintptr_t held = jl_lock_profile_rd_held();
+    if (held)
+        return 0;
+    held = -1;
+#ifndef _OS_WINDOWS_
+    pthread_setspecific(debuginfo_asyncsafe_held, (void*)held);
+#else
+    TlsSetValue(debuginfo_asyncsafe_held, (void*)held);
+#endif
     uv_rwlock_wrlock(&debuginfo_asyncsafe);
+    return 1;
 }
 
 void jl_unlock_profile_wr(void)
 {
+    uintptr_t held = jl_lock_profile_rd_held();
+    assert(held == -1);
+    held = 0;
+#ifndef _OS_WINDOWS_
+    pthread_setspecific(debuginfo_asyncsafe_held, (void*)held);
+#else
+    TlsSetValue(debuginfo_asyncsafe_held, (void*)held);
+#endif
     uv_rwlock_wrunlock(&debuginfo_asyncsafe);
 }
 

src/threading.c

@@ -559,18 +559,20 @@ static void jl_delete_thread(void *value) JL_NOTSAFEPOINT_ENTER
     // this here by blocking. This also synchronizes our read of `current_task`
     // (which is the flag we currently use to check the liveness state of a thread).
 #ifdef _OS_WINDOWS_
-    jl_lock_profile_wr();
+    int havelock = jl_lock_profile_wr();
+    assert(havelock); (void)havelock;
 #elif defined(JL_DISABLE_LIBUNWIND)
     // nothing
 #elif defined(__APPLE__)
-    jl_lock_profile_wr();
+    int havelock = jl_lock_profile_wr();
+    assert(havelock); (void)havelock;
 #else
     pthread_mutex_lock(&in_signal_lock);
 #endif
     jl_atomic_store_relaxed(&ptls->current_task, NULL); // indicate dead
     // finally, release all of the locks we had grabbed
 #ifdef _OS_WINDOWS_
-    jl_unlock_profile_wr();
+    if (havelock) jl_unlock_profile_wr();
 #elif defined(JL_DISABLE_LIBUNWIND)
     // nothing
 #elif defined(__APPLE__)