[POWERPC] spufs: block fault handlers in spu_acquire_runnable

This change disables the logic that faults-in spu contexts under the
covers from the page fault handler.  When a fault requires a runnable
context, the handler will block until the context is scheduled by
other means.
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/cell/spufs/context.c

@@ -52,6 +52,7 @@ struct spu_context *alloc_spu_context(struct spu_gang *gang)
 	init_waitqueue_head(&ctx->wbox_wq);
 	init_waitqueue_head(&ctx->stop_wq);
 	init_waitqueue_head(&ctx->mfc_wq);
+	init_waitqueue_head(&ctx->run_wq);
 	ctx->state = SPU_STATE_SAVED;
 	ctx->ops = &spu_backing_ops;
 	ctx->owner = get_task_mm(current);

arch/powerpc/platforms/cell/spufs/file.c

@@ -236,21 +236,31 @@ static unsigned long spufs_ps_nopfn(struct vm_area_struct *vma,
 {
 	struct spu_context *ctx = vma->vm_file->private_data;
 	unsigned long area, offset = address - vma->vm_start;
-	int ret;
 
 	offset += vma->vm_pgoff << PAGE_SHIFT;
 	if (offset >= ps_size)
 		return NOPFN_SIGBUS;
 
-	/* error here usually means a signal.. we might want to test
-	 * the error code more precisely though
+	/*
+	 * We have to wait for context to be loaded before we have
+	 * pages to hand out to the user, but we don't want to wait
+	 * with the mmap_sem held.
+	 * It is possible to drop the mmap_sem here, but then we need
+	 * to return NOPFN_REFAULT because the mappings may have
+	 * hanged.
 	 */
-	ret = spu_acquire_runnable(ctx, 0);
-	if (ret)
-		return NOPFN_REFAULT;
+	spu_acquire(ctx);
+	if (ctx->state == SPU_STATE_SAVED) {
+		up_read(&current->mm->mmap_sem);
+		spufs_wait(ctx->run_wq, ctx->state == SPU_STATE_RUNNABLE);
+		down_read(&current->mm->mmap_sem);
+		goto out;
+	}
 
 	area = ctx->spu->problem_phys + ps_offs;
 	vm_insert_pfn(vma, address, (area + offset) >> PAGE_SHIFT);
+
+out:
 	spu_release(ctx);
 
 	return NOPFN_REFAULT;
@@ -1505,7 +1515,8 @@ static ssize_t spufs_mfc_write(struct file *file, const char __user *buffer,
 	if (ret)
 		goto out;
 
-	ret = spu_acquire_runnable(ctx, 0);
+	spu_acquire(ctx);
+	ret = spufs_wait(ctx->run_wq, ctx->state == SPU_STATE_RUNNABLE);
 	if (ret)
 		goto out;
 

arch/powerpc/platforms/cell/spufs/sched.c

@@ -682,6 +682,7 @@ int spu_activate(struct spu_context *ctx, unsigned long flags)
 			spu_bind_context(spu, ctx);
 			cbe_spu_info[node].nr_active++;
 			mutex_unlock(&cbe_spu_info[node].list_mutex);
+			wake_up_all(&ctx->run_wq);
 			return 0;
 		}
 

arch/powerpc/platforms/cell/spufs/spufs.h

@@ -71,6 +71,7 @@ struct spu_context {
 	wait_queue_head_t wbox_wq;
 	wait_queue_head_t stop_wq;
 	wait_queue_head_t mfc_wq;
+	wait_queue_head_t run_wq;
 	struct fasync_struct *ibox_fasync;
 	struct fasync_struct *wbox_fasync;
 	struct fasync_struct *mfc_fasync;