malloc: fix race condition and other bugs in the no-mmu malloc

Fixes multiple race conditions on mmb list. This was done by
making the mmb_heap_lock into a recursive lock and making the
regular heap_lock extend to cover the mmb heap handling.

Also move the new_mmb allocation up to before the mmb list is
iterated through to find the insertion point. When the mmb_heap
also runs out and needs to be extended when the regular heap is
just extended, the mmb list could be messed up.

Signed-off-by: Freeman Wang <xwang@ubicom.com>
Signed-off-by: Austin Foxley <austinf@cetoncorp.com>

2 files changed, 7 insertions, 6 deletions

diff --git a/libc/stdlib/malloc/free.c b/libc/stdlib/malloc/free.c
index c17e7ec2a..e7b6a290a 100644
--- a/libc/stdlib/malloc/free.c
+++ b/libc/stdlib/malloc/free.c
@@ -177,14 +177,14 @@ __free_to_heap (void *mem, struct heap_free_area **heap
 	      /* Start searching again from the end of this block.  */
 	      start = mmb_end;
 
+	      /* Release the descriptor block we used.  */
+	      free_to_heap (mmb, &__malloc_mmb_heap, &__malloc_mmb_heap_lock);
+
 	      /* We have to unlock the heap before we recurse to free the mmb
 		 descriptor, because we might be unmapping from the mmb
 		 heap.  */
               __heap_unlock (heap_lock);
 
-	      /* Release the descriptor block we used.  */
-	      free_to_heap (mmb, &__malloc_mmb_heap, &__malloc_mmb_heap_lock);
-
 	      /* Do the actual munmap.  */
 	      munmap ((void *)mmb_start, mmb_end - mmb_start);
 
diff --git a/libc/stdlib/malloc/malloc.c b/libc/stdlib/malloc/malloc.c
index 337206f09..d58a7d0ee 100644
--- a/libc/stdlib/malloc/malloc.c
+++ b/libc/stdlib/malloc/malloc.c
@@ -46,7 +46,7 @@ struct malloc_mmb *__malloc_mmapped_blocks = 0;
 HEAP_DECLARE_STATIC_FREE_AREA (initial_mmb_fa, 48); /* enough for 3 mmbs */
 struct heap_free_area *__malloc_mmb_heap = HEAP_INIT_WITH_FA (initial_mmb_fa);
 #ifdef HEAP_USE_LOCKING
-malloc_mutex_t __malloc_mmb_heap_lock = PTHREAD_MUTEX_INITIALIZER;
+malloc_mutex_t __malloc_mmb_heap_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
 #endif
 #endif /* __UCLIBC_UCLINUX_BROKEN_MUNMAP__ */
 
@@ -149,19 +149,19 @@ __malloc_from_heap (size_t size, struct heap_free_area **heap
 	  /* Try again to allocate.  */
 	  mem = __heap_alloc (heap, &size);
 
-	  __heap_unlock (heap_lock);
 
 #if !defined(MALLOC_USE_SBRK) && defined(__UCLIBC_UCLINUX_BROKEN_MUNMAP__)
 	  /* Insert a record of BLOCK in sorted order into the
 	     __malloc_mmapped_blocks list.  */
 
+	  new_mmb = malloc_from_heap (sizeof *new_mmb, &__malloc_mmb_heap, &__malloc_mmb_heap_lock);
+
 	  for (prev_mmb = 0, mmb = __malloc_mmapped_blocks;
 	       mmb;
 	       prev_mmb = mmb, mmb = mmb->next)
 	    if (block < mmb->mem)
 	      break;
 
-	  new_mmb = malloc_from_heap (sizeof *new_mmb, &__malloc_mmb_heap, &__malloc_mmb_heap_lock);
 	  new_mmb->next = mmb;
 	  new_mmb->mem = block;
 	  new_mmb->size = block_size;
@@ -175,6 +175,7 @@ __malloc_from_heap (size_t size, struct heap_free_area **heap
 			    (unsigned)new_mmb,
 			    (unsigned)new_mmb->mem, block_size);
 #endif /* !MALLOC_USE_SBRK && __UCLIBC_UCLINUX_BROKEN_MUNMAP__ */
+	  __heap_unlock (heap_lock);
 	}
     }