Work around an assert failure in the dynamic linker's default thread

locking functions.  If an application loads a shared object with
dlopen() and the shared object has an init function which requires
lazy binding, then _rtld_bind is called when the thread is already
inside the dynamic linker.  This leads to a recursive acquisition
of the lock, which I was not expecting -- hence the assert failure.

This work-around makes the default locking functions handle recursive
locking.  It is NOT the correct fix -- that should be implemented
at the generic locking level rather than in the default locking
functions.  I will implement the correct fix in a future commit.

Since the dllockinit() interface will likely need to change, warn
about that in both the man page and the header file.

include/dlfcn.h

@@ -66,6 +66,7 @@ __BEGIN_DECLS
 int dladdr __P((const void *, Dl_info *));
 int dlclose __P((void *));
 const char *dlerror __P((void));
+/* XXX dllockinit() interface is likely to change. */
 void dllockinit __P((void *_context,
 		     void *(*_lock_create)(void *_context),
 		     void (*_rlock_acquire)(void *_lock),

lib/libc/gen/dllockinit.3

@@ -39,6 +39,10 @@
 "void (*lock_release)(void *lock)" "void (*lock_destroy)(void *lock)" \
 "void (*context_destroy)(void *context)"
 .Sh DESCRIPTION
+.Bf Sy
+This interface is subject to change and should not be used yet.
+.Ef
+.Pp
 Threads packages can call
 .Nm
 at initialization time to register locking functions for the dynamic

libexec/rtld-elf/alpha/lockdflt.c

@@ -51,8 +51,11 @@ void
 lockdflt_acquire(void *lock)
 {
     LockDflt *l = (LockDflt *)lock;
-    sigprocmask(SIG_BLOCK, &l->lock_mask, &l->old_mask);
-    assert(l->depth == 0);
+    sigset_t old_mask;
+
+    sigprocmask(SIG_BLOCK, &l->lock_mask, &old_mask);
+    if (l->depth == 0)
+	l->old_mask = old_mask;
     l->depth++;
 }
 
@@ -81,9 +84,10 @@ void
 lockdflt_release(void *lock)
 {
     LockDflt *l = (LockDflt *)lock;
-    assert(l->depth == 1);
     l->depth--;
-    sigprocmask(SIG_SETMASK, &l->old_mask, NULL);
+    assert(l->depth >= 0);
+    if (l->depth == 0)
+	sigprocmask(SIG_SETMASK, &l->old_mask, NULL);
 }
 
 void

libexec/rtld-elf/amd64/lockdflt.c

@@ -51,8 +51,11 @@ void
 lockdflt_acquire(void *lock)
 {
     LockDflt *l = (LockDflt *)lock;
-    sigprocmask(SIG_BLOCK, &l->lock_mask, &l->old_mask);
-    assert(l->depth == 0);
+    sigset_t old_mask;
+
+    sigprocmask(SIG_BLOCK, &l->lock_mask, &old_mask);
+    if (l->depth == 0)
+	l->old_mask = old_mask;
     l->depth++;
 }
 
@@ -81,9 +84,10 @@ void
 lockdflt_release(void *lock)
 {
     LockDflt *l = (LockDflt *)lock;
-    assert(l->depth == 1);
     l->depth--;
-    sigprocmask(SIG_SETMASK, &l->old_mask, NULL);
+    assert(l->depth >= 0);
+    if (l->depth == 0)
+	sigprocmask(SIG_SETMASK, &l->old_mask, NULL);
 }
 
 void

libexec/rtld-elf/i386/lockdflt.c

@@ -51,8 +51,11 @@ void
 lockdflt_acquire(void *lock)
 {
     LockDflt *l = (LockDflt *)lock;
-    sigprocmask(SIG_BLOCK, &l->lock_mask, &l->old_mask);
-    assert(l->depth == 0);
+    sigset_t old_mask;
+
+    sigprocmask(SIG_BLOCK, &l->lock_mask, &old_mask);
+    if (l->depth == 0)
+	l->old_mask = old_mask;
     l->depth++;
 }
 
@@ -81,9 +84,10 @@ void
 lockdflt_release(void *lock)
 {
     LockDflt *l = (LockDflt *)lock;
-    assert(l->depth == 1);
     l->depth--;
-    sigprocmask(SIG_SETMASK, &l->old_mask, NULL);
+    assert(l->depth >= 0);
+    if (l->depth == 0)
+	sigprocmask(SIG_SETMASK, &l->old_mask, NULL);
 }
 
 void

libexec/rtld-elf/lockdflt.c

@@ -51,8 +51,11 @@ void
 lockdflt_acquire(void *lock)
 {
     LockDflt *l = (LockDflt *)lock;
-    sigprocmask(SIG_BLOCK, &l->lock_mask, &l->old_mask);
-    assert(l->depth == 0);
+    sigset_t old_mask;
+
+    sigprocmask(SIG_BLOCK, &l->lock_mask, &old_mask);
+    if (l->depth == 0)
+	l->old_mask = old_mask;
     l->depth++;
 }
 
@@ -81,9 +84,10 @@ void
 lockdflt_release(void *lock)
 {
     LockDflt *l = (LockDflt *)lock;
-    assert(l->depth == 1);
     l->depth--;
-    sigprocmask(SIG_SETMASK, &l->old_mask, NULL);
+    assert(l->depth >= 0);
+    if (l->depth == 0)
+	sigprocmask(SIG_SETMASK, &l->old_mask, NULL);
 }
 
 void