Mixed changes

- Adding prefaulting of fs0 to avoid page fault deadlocks.
- Fixed a bug that a vmo page_cache equivalence would simply drop a link to
  an original vmo, even if the vmo could have more pages outside the page cache,
  or if the vmo was not a shadow vmo.
- Fixed a bug with page allocator where recursion would corrupt global variables.
- Now going to fix or re-write a simpler page allocator that works.

src/arch/arm/exception.c

@@ -18,7 +18,7 @@
 #include INC_SUBARCH(mm.h)
 
 /* Abort debugging conditions */
-// #define DEBUG_ABORTS
+#define DEBUG_ABORTS
 #if defined (DEBUG_ABORTS)
 #define dbg_abort(...)	dprintk(__VA_ARGS__)
 #else

tasks/libmem/mm/alloc_page.c

@@ -19,6 +19,7 @@
 struct page_allocator allocator;
 
 static struct mem_cache *new_dcache();
+static int find_and_free_page_area(void *addr, struct page_allocator *p);
 
 /*
  * Allocate a new page area from @area_sources_start. If no areas left,
@@ -63,25 +64,46 @@ get_free_page_area(int quantity, struct page_allocator *p,
 	if (quantity <= 0)
 		return 0;
 
+	/*
+	 * First, allocate a new area, which may involve recursion.
+	 * If we call this while we touch the global area list, we will
+	 * corrupt it so we call it first.
+	 */
+	if (!(new = new_page_area(p, cache_list)))
+		return 0; /* No more pages */
+
 	list_for_each_entry(area, &p->page_area_list, list) {
-		/* Free but needs dividing */
+
+		/* Check for exact size match */
+		if (area->numpages == quantity && !area->used) {
+			/* Mark it as used */
+			area->used = 1;
+
+		 	/*
+			 * We don't need the area we allocated
+			 * earlier, just free it.
+			 */
+			BUG_ON(find_and_free_page_area(
+				(void *)__pfn_to_addr(new->pfn), p) < 0);
+			return area;
+		}
+
 		if (area->numpages > quantity && !area->used) {
 			area->numpages -= quantity;
-			if (!(new = new_page_area(p, cache_list)))
-				return 0; /* No more pages */
 			new->pfn = area->pfn + area->numpages;
 			new->numpages = quantity;
 			new->used = 1;
 			INIT_LIST_HEAD(&new->list);
 			list_add(&new->list, &area->list);
 			return new;
-		/* Free and exact size match, no need to divide. */
-		} else if (area->numpages == quantity && !area->used) {
-			area->used = 1;
-			return area;
 		}
 	}
-	/* No more pages */
+
+ 	/*
+	 * No more pages. We could not use the area
+	 * we allocated earlier, just free it.
+	 */
+	find_and_free_page_area((void *)__pfn_to_addr(new->pfn), p);
 	return 0;
 }
 

tasks/libposix/README

@@ -3,18 +3,17 @@ libposix
 
 Copyright (C) 2007 Bahadir Balban
 
-Despite the name, this is a library that supports only a tiny portion of posix functions.
-
-Currently supported functions are:
+Despite the name, this is a library that supports only a small portion of posix functions.
 
 
-Functions to be supported in the near future are:
+Highest priority POSIX functions are:
 
 shmat
 shmget
 shmdt
 mmap
 munmap
+sbrk
 read
 readdir
 write
@@ -27,12 +26,50 @@ mknod
 link
 unlink
 fork
+clone
 execve
 getpid
 wait
 kill
+getenv
+setenv
 
-Others:
+
+Currently supported functions are:
+
+shmat
+shmget
+shmdt
+mmap
+read
+readdir
+write
+lseek
+open
+close
+creat
+mkdir
+mknod
+fork
+
+
+Functions to be supported in the near future are:
+
+munmap
+link
+unlink
+getpid
+execve
+clone
+wait
+kill
+exit
+sbrk
+getenv
+setenv
+
+
+Other calls:
 pipe
 mount
 unmount

tasks/mm0/include/vm_area.h

@@ -14,7 +14,7 @@
 #include <arch/mm.h>
 #include <lib/spinlock.h>
 
-// #define DEBUG_FAULT_HANDLING
+#define DEBUG_FAULT_HANDLING
 #ifdef DEBUG_FAULT_HANDLING
 #define dprintf(...)	printf(__VA_ARGS__)
 #else

tasks/mm0/main.c

@@ -148,11 +148,53 @@ void handle_requests(void)
 	}
 }
 
+#if 0
+int self_spawn(void)
+{
+	struct task_ids ids;
+	struct tcb *self, *self_child;
+
+	BUG_ON(!(self = find_task(self_tid())));
+
+	ids.tid = THREAD_ID_INVALID;
+	ids.spid = self->spid;
+
+	/* Create a new L4 thread in current thread's address space. */
+	self_child = task_create(&ids, THREAD_CREATE_SAMESPC);
+
+	/* Copy self tcb to child. TODO: ??? Not sure about this */
+	copy_tcb(self_child, self);
+
+	/*
+	 * Create a new utcb. Every pager thread will
+	 * need its own utcb to answer calls.
+	 */
+	self_child->utcb = utcb_vaddr_new();
+
+	/* TODO: Create a new utcb shm for own thread ??? Does it need to shmat??? */
+
+	/* TODO: Notify vfs ??? */
+
+	/* TODO: Modify registers ???, it depends on what state is copied in C0 */
+
+	task_add_global(self_child);
+
+	l4_thread_control(THREAD_RUN, &ids);
+}
+#endif
+
+
 void main(void)
 {
 	/* Initialise the memory, server tasks, mmap and start them. */
 	initialise();
 
+/*
+	if (self_spawn())
+		while (1)
+			;
+*/
+
 	while (1) {
 		handle_requests();
 	}

tasks/mm0/src/fault.c

@@ -96,24 +96,27 @@ struct vm_object *vma_drop_link(struct vm_obj_link *shadower_link,
 
 /*
  * Checks if page cache pages of lesser is a subset of those of copier.
+ *
+ * FIXME:
  * Note this just checks the page cache, so if any objects have pages
- * swapped to disk, this function does not rule.
+ * swapped to disk, this function won't work, which is a logic error.
+ * This should really count the swapped ones as well.
  */
-int vm_object_is_subset(struct vm_object *copier,
-			struct vm_object *lesser)
+int vm_object_is_subset(struct vm_object *shadow,
+			struct vm_object *original)
 {
 	struct page *pc, *pl;
 
 	/* Copier must have equal or more pages to overlap lesser */
-	if (copier->npages < lesser->npages)
+	if (shadow->npages < original->npages)
 		return 0;
 
 	/*
 	 * Do a page by page comparison. Every lesser page
 	 * must be in copier for overlap.
 	 */
-	list_for_each_entry(pl, &lesser->page_cache, list)
-		if (!(pc = find_page(copier, pl->offset)))
+	list_for_each_entry(pl, &original->page_cache, list)
+		if (!(pc = find_page(shadow, pl->offset)))
 			return 0;
 	/*
 	 * For all pages of lesser vmo, there seems to be a page
@@ -122,6 +125,16 @@ int vm_object_is_subset(struct vm_object *copier,
 	return 1;
 }
 
+static inline int vm_object_is_droppable(struct vm_object *shadow,
+					 struct vm_object *original)
+{
+	if (vm_object_is_subset(shadow, original)
+	    && (original->flags & VM_OBJ_SHADOW))
+		return 1;
+	else
+		return 0;
+}
+
 /*
  * When one shadow object is redundant, merges it into the shadow in front of it.
  * Note it must be determined that it is redundant before calling this function.
@@ -231,8 +244,7 @@ struct page *copy_to_new_page(struct page *orig)
 	void *new_vaddr, *vaddr, *paddr;
 	struct page *new;
 
-	if (!(paddr = alloc_page(1)))
-		return 0;
+	BUG_ON(!(paddr = alloc_page(1)));
 
 	new = phys_to_page(paddr);
 
@@ -258,8 +270,8 @@ struct page *copy_to_new_page(struct page *orig)
 int vma_drop_merge_delete(struct vm_obj_link *shadow_link,
 			  struct vm_obj_link *orig_link)
 {
-	/* Can we can drop one link? */
-	if (vm_object_is_subset(shadow_link->obj, orig_link->obj)) {
+	/* Can we drop one link? */
+	if (vm_object_is_droppable(shadow_link->obj, orig_link->obj)) {
 		struct vm_object *dropped;
 
 		dprintf("VM OBJECT is a subset of its shadow.\nShadow:\n");

tasks/mm0/src/task.c

@@ -258,6 +258,28 @@ int mm0_task_init(struct vm_file *f, unsigned long task_start,
 	return 0;
 }
 
+/*
+ * Prefaults all mapped regions of a task. The reason we have this is
+ * some servers are in the page fault handling path (e.g. fs0), and we
+ * don't want them to fault and cause deadlocks and circular deps.
+ *
+ * Normally fs0 faults dont cause dependencies because its faults
+ * are handled by the boot pager, which is part of mm0. BUT: It may
+ * cause deadlocks because fs0 may fault while serving a request
+ * from mm0.(Which is expected to also handle the fault).
+ */
+int task_prefault_regions(struct tcb *task, struct vm_file *f)
+{
+	struct vm_area *vma;
+
+	list_for_each_entry(vma, &task->vm_area_list, list) {
+		for (int pfn = vma->pfn_start; pfn < vma->pfn_end; pfn++)
+			BUG_ON(prefault_page(task, __pfn_to_addr(pfn),
+					     VM_READ | VM_WRITE) < 0);
+	}
+	return 0;
+}
+
 /*
  * Main entry point for the creation, initialisation and
  * execution of a new task.
@@ -278,6 +300,10 @@ int task_exec(struct vm_file *f, unsigned long task_region_start,
 	if ((err = task_mmap_regions(task, f)) < 0)
 		return err;
 
+	if (ids->tid == VFS_TID)
+		if ((err = task_prefault_regions(task, f)) < 0)
+			return err;
+
 	if ((err =  task_setup_registers(task, 0, 0, 0)) < 0)
 		return err;