[PATCH] malloc: Ensure that ptmalloc_init runs only once

[Siddhesh Poyarekar <siddhesh@sourceware.org>]

It is possible that multiple threads simultaneously enter
ptmalloc_init and succeed the < 0 check.  Make the comparison and
setting of __malloc_initialized atomic so that only one of them goes
through.  Additionally, if a thread sees that another thread is
running the initialization (i.e. __malloc_initialized == 0) then wait
till it is done.
---
 malloc/arena.c  | 12 +++++++++---
 malloc/malloc.c | 14 +++++++-------
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/malloc/arena.c b/malloc/arena.c
index 7eb110445e..3cd4391f25 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -290,10 +290,16 @@ libc_hidden_proto (_dl_open_hook);
 static void
 ptmalloc_init (void)
 {
-  if (__malloc_initialized >= 0)
-    return;
+  int oldval = catomic_compare_and_exchange_val_acq (&__malloc_initialized,
+						     -1, 0);
 
-  __malloc_initialized = 0;
+  if (oldval == 1)
+    return;
+  else if (oldval == 0)
+    {
+      while (__malloc_initialized != 1);
+      return;
+    }
 
 #ifdef USE_MTAG
   if ((TUNABLE_GET_FULL (glibc, mem, tagging, int32_t, NULL) & 1) != 0)
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 0e2e1747e0..cc3d1f41e8 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -3562,7 +3562,7 @@ libc_hidden_def (__libc_memalign)
 void *
 __libc_valloc (size_t bytes)
 {
-  if (__malloc_initialized < 0)
+  if (__malloc_initialized <= 0)
     ptmalloc_init ();
 
   void *address = RETURN_ADDRESS (0);
@@ -3573,7 +3573,7 @@ __libc_valloc (size_t bytes)
 void *
 __libc_pvalloc (size_t bytes)
 {
-  if (__malloc_initialized < 0)
+  if (__malloc_initialized <= 0)
     ptmalloc_init ();
 
   void *address = RETURN_ADDRESS (0);
@@ -5077,7 +5077,7 @@ __malloc_trim (size_t s)
 {
   int result = 0;
 
-  if (__malloc_initialized < 0)
+  if (__malloc_initialized <= 0)
     ptmalloc_init ();
 
   mstate ar_ptr = &main_arena;
@@ -5212,7 +5212,7 @@ __libc_mallinfo2 (void)
   struct mallinfo2 m;
   mstate ar_ptr;
 
-  if (__malloc_initialized < 0)
+  if (__malloc_initialized <= 0)
     ptmalloc_init ();
 
   memset (&m, 0, sizeof (m));
@@ -5263,7 +5263,7 @@ __malloc_stats (void)
   mstate ar_ptr;
   unsigned int in_use_b = mp_.mmapped_mem, system_b = in_use_b;
 
-  if (__malloc_initialized < 0)
+  if (__malloc_initialized <= 0)
     ptmalloc_init ();
   _IO_flockfile (stderr);
   int old_flags2 = stderr->_flags2;
@@ -5432,7 +5432,7 @@ __libc_mallopt (int param_number, int value)
   mstate av = &main_arena;
   int res = 1;
 
-  if (__malloc_initialized < 0)
+  if (__malloc_initialized <= 0)
     ptmalloc_init ();
   __libc_lock_lock (av->mutex);
 
@@ -5691,7 +5691,7 @@ __malloc_info (int options, FILE *fp)
 
 
 
-  if (__malloc_initialized < 0)
+  if (__malloc_initialized <= 0)
     ptmalloc_init ();
 
   fputs ("<malloc version=\"1\">\n", fp);
-- 
2.31.1