aio: do fget() after aio_get_req()

aio_get_req() will fail if we have the maximum number of requests
outstanding, which depending on the application may not be uncommon.  So
avoid doing an unnecessary fget().

Signed-off-by: Kent Overstreet <koverstreet@google.com>
Cc: Zach Brown <zab@redhat.com>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Asai Thambi S P <asamymuthupa@micron.com>
Cc: Selvan Mani <smani@micron.com>
Cc: Sam Bradshaw <sbradshaw@micron.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Reviewed-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/aio.c

@@ -587,6 +587,8 @@ static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
 {
 	assert_spin_locked(&ctx->ctx_lock);
 
+	if (req->ki_filp)
+		fput(req->ki_filp);
 	if (req->ki_eventfd != NULL)
 		eventfd_ctx_put(req->ki_eventfd);
 	if (req->ki_dtor)
@@ -605,9 +607,6 @@ static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
  */
 static void __aio_put_req(struct kioctx *ctx, struct kiocb *req)
 {
-	pr_debug("(%p): f_count=%ld\n",
-		 req, atomic_long_read(&req->ki_filp->f_count));
-
 	assert_spin_locked(&ctx->ctx_lock);
 
 	req->ki_users--;
@@ -618,8 +617,6 @@ static void __aio_put_req(struct kioctx *ctx, struct kiocb *req)
 	req->ki_cancel = NULL;
 	req->ki_retry = NULL;
 
-	fput(req->ki_filp);
-	req->ki_filp = NULL;
 	really_put_req(ctx, req);
 }
 
@@ -1270,7 +1267,6 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
 			 bool compat)
 {
 	struct kiocb *req;
-	struct file *file;
 	ssize_t ret;
 
 	/* enforce forwards compatibility on users */
@@ -1289,16 +1285,16 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
 		return -EINVAL;
 	}
 
-	file = fget(iocb->aio_fildes);
-	if (unlikely(!file))
-		return -EBADF;
-
 	req = aio_get_req(ctx, batch);  /* returns with 2 references to req */
-	if (unlikely(!req)) {
-		fput(file);
+	if (unlikely(!req))
 		return -EAGAIN;
+
+	req->ki_filp = fget(iocb->aio_fildes);
+	if (unlikely(!req->ki_filp)) {
+		ret = -EBADF;
+		goto out_put_req;
 	}
-	req->ki_filp = file;
+
 	if (iocb->aio_flags & IOCB_FLAG_RESFD) {
 		/*
 		 * If the IOCB_FLAG_RESFD flag of aio_flags is set, get an