aio: simplify KIOCB_KEY handling

No need to pass the key field to lookup_iocb to compare it with KIOCB_KEY,
as we can do that right after retrieving it from userspace.  Also move the
KIOCB_KEY definition to aio.c as it is an internal value not used by any
other place in the kernel.
Signed-off-by: Christoph Hellwig <hch@lst.de>

fs/aio.c

@@ -46,6 +46,8 @@
 
 #include "internal.h"
 
+#define KIOCB_KEY		0
+
 #define AIO_RING_MAGIC			0xa10a10a1
 #define AIO_RING_COMPAT_FEATURES	1
 #define AIO_RING_INCOMPAT_FEATURES	0
@@ -1811,15 +1813,12 @@ COMPAT_SYSCALL_DEFINE3(io_submit, compat_aio_context_t, ctx_id,
  *	Finds a given iocb for cancellation.
  */
 static struct aio_kiocb *
-lookup_kiocb(struct kioctx *ctx, struct iocb __user *iocb, u32 key)
+lookup_kiocb(struct kioctx *ctx, struct iocb __user *iocb)
 {
 	struct aio_kiocb *kiocb;
 
 	assert_spin_locked(&ctx->ctx_lock);
 
-	if (key != KIOCB_KEY)
-		return NULL;
-
 	/* TODO: use a hash or array, this sucks. */
 	list_for_each_entry(kiocb, &ctx->active_reqs, ki_list) {
 		if (kiocb->ki_user_iocb == iocb)
@@ -1846,9 +1845,10 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
 	u32 key;
 	int ret;
 
-	ret = get_user(key, &iocb->aio_key);
-	if (unlikely(ret))
+	if (unlikely(get_user(key, &iocb->aio_key)))
 		return -EFAULT;
+	if (unlikely(key != KIOCB_KEY))
+		return -EINVAL;
 
 	ctx = lookup_ioctx(ctx_id);
 	if (unlikely(!ctx))
@@ -1856,7 +1856,7 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
 
 	spin_lock_irq(&ctx->ctx_lock);
 
-	kiocb = lookup_kiocb(ctx, iocb, key);
+	kiocb = lookup_kiocb(ctx, iocb);
 	if (kiocb)
 		ret = kiocb_cancel(kiocb);
 	else

include/linux/aio.h

@@ -8,8 +8,6 @@ struct kioctx;
 struct kiocb;
 struct mm_struct;
 
-#define KIOCB_KEY		0
-
 typedef int (kiocb_cancel_fn)(struct kiocb *);
 
 /* prototypes */