Cygwin: split malloc_init

Cygwin 3.3 only: Replace SRWLOCK usage for malloc synchronization with
the first incarnation of the patch splitting malloc_init into two parts.
The SRWLOCK usage requires TryAcquireSRWLockExclusive, which isn't
available on Vista / Server 2008, unfortunately.

Per https://cygwin.com/pipermail/cygwin-developers/2021-October/012429.html,
we may encounter a crash when starting multiple threads during process
startup (here: fhandler_fifo::fixup_after_{fork,exec}) which in turn
allocate memory via malloc.

The problem is concurrent usage of malloc before the malloc muto has
been initialized.

To fix this issue, split malloc_init into malloc_init_0, called from
dll_crt0_0, and malloc_init_1, called from dll_crt_0_1.  malloc_init_0
just initializes the muto, malloc_init_1 checks for user space provided
malloc.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/cygmalloc.h

@@ -39,6 +39,8 @@ void *mmap64 (void *, size_t, int, int, int, off_t);
 # define __malloc_lock() mallock.acquire ()
 # define __malloc_unlock() mallock.release ()
 extern muto mallock;
+inline void malloc_init_0 () { mallock.init ("mallock"); }
+extern void malloc_init_1 ();
 
 #endif
 

winsup/cygwin/dcrt0.cc

@@ -29,6 +29,7 @@ details. */
 #include "shared_info.h"
 #include "cygwin_version.h"
 #include "dll_init.h"
+#include "cygmalloc.h"
 #include "heap.h"
 #include "tls_pbuf.h"
 #include "exception.h"
@@ -769,6 +770,8 @@ dll_crt0_0 ()
   NtOpenProcessToken (NtCurrentProcess (), MAXIMUM_ALLOWED, &hProcToken);
   set_cygwin_privileges (hProcToken);
 
+  malloc_init_0 ();
+
   device::init ();
   do_global_ctors (&__CTOR_LIST__, 1);
   cygthread::init ();
@@ -857,7 +860,7 @@ dll_crt0_1 (void *)
      on a functioning malloc and it's possible that the user's program may
      have overridden malloc.  We only know about that at this stage,
      unfortunately. */
-  malloc_init ();
+  malloc_init_1 ();
   user_shared->initialize ();
 
 #ifdef CYGHEAP_DEBUG

winsup/cygwin/heap.cc

@@ -230,7 +230,6 @@ user_heap_info::init ()
   debug_printf ("heap base %p, heap top %p, heap size %ly (%lu)",
 		base, top, chunk, chunk);
   page_const--;
-  // malloc_init ();
 }
 
 #define pround(n) (((size_t)(n) + page_const) & ~page_const)

winsup/cygwin/heap.h

@@ -10,7 +10,6 @@ details. */
 
 /* Heap management. */
 void heap_init ();
-void malloc_init ();
 
 #define inheap(s) \
   (cygheap->user_heap.ptr && s \

winsup/cygwin/malloc_wrapper.cc

@@ -272,10 +272,8 @@ strdup (const char *s)
 muto NO_COPY mallock;
 
 void
-malloc_init ()
+malloc_init_1 ()
 {
-  mallock.init ("mallock");
-
   /* Check if malloc is provided by application. If so, redirect all
      calls to malloc/free/realloc to application provided. This may
      happen if some other dll calls cygwin's malloc, but main code provides

winsup/cygwin/release/3.3.1

@@ -0,0 +1,6 @@
+Bug Fixes
+---------
+
+- Fix a fix in 3.3.0 which broke Vista / Server 2008 by using a Windows
+  function introduced with Windows 7 only, namely TryAcquireSRWLockExclusive.
+  Addresses: https://cygwin.com/pipermail/cygwin/2021-October/249732.html