[PATCH] spufs: serialize sys_spu_run per spu

During an earlier cleanup, we lost the serialization
of multiple spu_run calls performed on the same
spu_context. In order to get this back, introduce a
mutex in the spu_context that is held inside of spu_run.

Noticed by Al Viro.

Signed-off-by: Arnd Bergmann <arndb@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

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

@@ -43,6 +43,7 @@ struct spu_context *alloc_spu_context(struct address_space *local_store)
 	spin_lock_init(&ctx->mmio_lock);
 	kref_init(&ctx->kref);
 	init_rwsem(&ctx->state_sema);
+	init_MUTEX(&ctx->run_sema);
 	init_waitqueue_head(&ctx->ibox_wq);
 	init_waitqueue_head(&ctx->wbox_wq);
 	init_waitqueue_head(&ctx->stop_wq);

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

@@ -620,18 +620,21 @@ long spufs_run_spu(struct file *file, struct spu_context *ctx,
 {
 	int ret;
 
-	if ((ret = spu_run_init(ctx, npc, status)) != 0)
-		return ret;
+	if (down_interruptible(&ctx->run_sema))
+		return -ERESTARTSYS;
+
+	ret = spu_run_init(ctx, npc, status);
+	if (ret)
+		goto out;
 
 	do {
 		ret = spufs_wait(ctx->stop_wq, spu_stopped(ctx, status));
 		if (unlikely(ret))
 			break;
 		if (unlikely(ctx->state != SPU_STATE_RUNNABLE)) {
 			ret = spu_reacquire_runnable(ctx, npc, status);
-			if (ret) {
-				return ret;
-			}
+			if (ret)
+				goto out;
 			continue;
 		}
 		ret = spu_process_events(ctx);
@@ -645,6 +648,8 @@ long spufs_run_spu(struct file *file, struct spu_context *ctx,
 		ret = *status;
 	spu_yield(ctx);
 
+out:
+	up(&ctx->run_sema);
 	return ret;
 }
 

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

@@ -48,6 +48,7 @@ struct spu_context {
 
 	enum { SPU_STATE_RUNNABLE, SPU_STATE_SAVED } state;
 	struct rw_semaphore state_sema;
+	struct semaphore run_sema;
 
 	struct mm_struct *owner;