[PATCH 1/5] fs: don't allow to complete sync iocbs through aio_complete

[Christoph Hellwig <hch@lst.de>]

The AIO interface is fairly complex because it tries to allow
filesystems to always work async and then wakeup a synchronous
caller through aio_complete.  It turns out that basically no one
does this to avoid the complexity and context switches, with the
solve exception of fuse, so remove that possibility to simplify
the code.

XXX: fix up fuse.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/usb/gadget/function/f_fs.c |  4 ++--
 fs/aio.c                           | 24 +-----------------------
 fs/ecryptfs/file.c                 |  6 ------
 fs/fuse/file.c                     |  7 +++++--
 fs/read_write.c                    | 26 ++++++++------------------
 include/linux/aio.h                |  4 ----
 net/socket.c                       |  9 +++------
 7 files changed, 19 insertions(+), 61 deletions(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 63314ed..debd78b 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -969,7 +969,7 @@ static ssize_t ffs_epfile_aio_write(struct kiocb *kiocb,
 	if (unlikely(!io_data))
 		return -ENOMEM;
 
-	io_data->aio = true;
+	io_data->aio = !is_sync_kiocb(kiocb);
 	io_data->read = false;
 	io_data->kiocb = kiocb;
 	io_data->iovec = iovec;
@@ -1005,7 +1005,7 @@ static ssize_t ffs_epfile_aio_read(struct kiocb *kiocb,
 		return -ENOMEM;
 	}
 
-	io_data->aio = true;
+	io_data->aio = !is_sync_kiocb(kiocb);
 	io_data->read = true;
 	io_data->kiocb = kiocb;
 	io_data->iovec = iovec_copy;
diff --git a/fs/aio.c b/fs/aio.c
index 1b7893e..0ee25d6 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -791,22 +791,6 @@ static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
 	return 0;
 }
 
-/* wait_on_sync_kiocb:
- *	Waits on the given sync kiocb to complete.
- */
-ssize_t wait_on_sync_kiocb(struct kiocb *req)
-{
-	while (!req->ki_ctx) {
-		set_current_state(TASK_UNINTERRUPTIBLE);
-		if (req->ki_ctx)
-			break;
-		io_schedule();
-	}
-	__set_current_state(TASK_RUNNING);
-	return req->ki_user_data;
-}
-EXPORT_SYMBOL(wait_on_sync_kiocb);
-
 /*
  * exit_aio: called when the last user of mm goes away.  At this point, there is
  * no way for any new requests to be submited or any of the io_* syscalls to be
@@ -1038,13 +1022,7 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
 	 *    ref, no other paths have a way to get another ref
 	 *  - the sync task helpfully left a reference to itself in the iocb
 	 */
-	if (is_sync_kiocb(iocb)) {
-		iocb->ki_user_data = res;
-		smp_wmb();
-		iocb->ki_ctx = ERR_PTR(-EXDEV);
-		wake_up_process(iocb->ki_obj.tsk);
-		return;
-	}
+	BUG_ON(is_sync_kiocb(iocb));
 
 	if (iocb->ki_list.next) {
 		unsigned long flags;
diff --git a/fs/ecryptfs/file.c b/fs/ecryptfs/file.c
index 6f4e659..a36da88 100644
--- a/fs/ecryptfs/file.c
+++ b/fs/ecryptfs/file.c
@@ -52,12 +52,6 @@ static ssize_t ecryptfs_read_update_atime(struct kiocb *iocb,
 	struct file *file = iocb->ki_filp;
 
 	rc = generic_file_read_iter(iocb, to);
-	/*
-	 * Even though this is a async interface, we need to wait
-	 * for IO to finish to update atime
-	 */
-	if (-EIOCBQUEUED == rc)
-		rc = wait_on_sync_kiocb(iocb);
 	if (rc >= 0) {
 		path = ecryptfs_dentry_to_lower_path(file->f_path.dentry);
 		touch_atime(path);
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 760b2c5..9c27312 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2841,8 +2841,10 @@ fuse_direct_IO(int rw, struct kiocb *iocb, struct iov_iter *iter,
 	/*
 	 * By default, we want to optimize all I/Os with async request
 	 * submission to the client filesystem if supported.
+	 *
+	 * XXX: need to add back support for this mode..
 	 */
-	io->async = async_dio;
+	io->async = async_dio && !is_sync_kiocb(iocb);
 	io->iocb = iocb;
 
 	/*
@@ -2865,7 +2867,8 @@ fuse_direct_IO(int rw, struct kiocb *iocb, struct iov_iter *iter,
 		if (!is_sync_kiocb(iocb))
 			return -EIOCBQUEUED;
 
-		ret = wait_on_sync_kiocb(iocb);
+		// XXX: need fuse specific replacement
+//		ret = wait_on_sync_kiocb(iocb);
 	} else {
 		kfree(io);
 	}
diff --git a/fs/read_write.c b/fs/read_write.c
index ab4f26a..adab608 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -347,9 +347,7 @@ ssize_t vfs_iter_read(struct file *file, struct iov_iter *iter, loff_t *ppos)
 
 	iter->type |= READ;
 	ret = file->f_op->read_iter(&kiocb, iter);
-	if (ret == -EIOCBQUEUED)
-		ret = wait_on_sync_kiocb(&kiocb);
-
+	BUG_ON(ret == -EIOCBQUEUED);
 	if (ret > 0)
 		*ppos = kiocb.ki_pos;
 	return ret;
@@ -370,9 +368,7 @@ ssize_t vfs_iter_write(struct file *file, struct iov_iter *iter, loff_t *ppos)
 
 	iter->type |= WRITE;
 	ret = file->f_op->write_iter(&kiocb, iter);
-	if (ret == -EIOCBQUEUED)
-		ret = wait_on_sync_kiocb(&kiocb);
-
+	BUG_ON(ret == -EIOCBQUEUED);
 	if (ret > 0)
 		*ppos = kiocb.ki_pos;
 	return ret;
@@ -429,8 +425,7 @@ ssize_t do_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *pp
 	kiocb.ki_nbytes = len;
 
 	ret = filp->f_op->aio_read(&kiocb, &iov, 1, kiocb.ki_pos);
-	if (-EIOCBQUEUED == ret)
-		ret = wait_on_sync_kiocb(&kiocb);
+	BUG_ON(ret == -EIOCBQUEUED);
 	*ppos = kiocb.ki_pos;
 	return ret;
 }
@@ -450,8 +445,7 @@ ssize_t new_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *p
 	iov_iter_init(&iter, READ, &iov, 1, len);
 
 	ret = filp->f_op->read_iter(&kiocb, &iter);
-	if (-EIOCBQUEUED == ret)
-		ret = wait_on_sync_kiocb(&kiocb);
+	BUG_ON(ret == -EIOCBQUEUED);
 	*ppos = kiocb.ki_pos;
 	return ret;
 }
@@ -513,8 +507,7 @@ ssize_t do_sync_write(struct file *filp, const char __user *buf, size_t len, lof
 	kiocb.ki_nbytes = len;
 
 	ret = filp->f_op->aio_write(&kiocb, &iov, 1, kiocb.ki_pos);
-	if (-EIOCBQUEUED == ret)
-		ret = wait_on_sync_kiocb(&kiocb);
+	BUG_ON(ret == -EIOCBQUEUED);
 	*ppos = kiocb.ki_pos;
 	return ret;
 }
@@ -534,8 +527,7 @@ ssize_t new_sync_write(struct file *filp, const char __user *buf, size_t len, lo
 	iov_iter_init(&iter, WRITE, &iov, 1, len);
 
 	ret = filp->f_op->write_iter(&kiocb, &iter);
-	if (-EIOCBQUEUED == ret)
-		ret = wait_on_sync_kiocb(&kiocb);
+	BUG_ON(ret == -EIOCBQUEUED);
 	*ppos = kiocb.ki_pos;
 	return ret;
 }
@@ -723,8 +715,7 @@ static ssize_t do_iter_readv_writev(struct file *filp, int rw, const struct iove
 
 	iov_iter_init(&iter, rw, iov, nr_segs, len);
 	ret = fn(&kiocb, &iter);
-	if (ret == -EIOCBQUEUED)
-		ret = wait_on_sync_kiocb(&kiocb);
+	BUG_ON(ret == -EIOCBQUEUED);
 	*ppos = kiocb.ki_pos;
 	return ret;
 }
@@ -740,8 +731,7 @@ static ssize_t do_sync_readv_writev(struct file *filp, const struct iovec *iov,
 	kiocb.ki_nbytes = len;
 
 	ret = fn(&kiocb, iov, nr_segs, kiocb.ki_pos);
-	if (ret == -EIOCBQUEUED)
-		ret = wait_on_sync_kiocb(&kiocb);
+	BUG_ON(ret == -EIOCBQUEUED);
 	*ppos = kiocb.ki_pos;
 	return ret;
 }
diff --git a/include/linux/aio.h b/include/linux/aio.h
index d9c92da..57c86c0 100644
--- a/include/linux/aio.h
+++ b/include/linux/aio.h
@@ -37,7 +37,6 @@ struct kiocb {
 
 	union {
 		void __user		*user;
-		struct task_struct	*tsk;
 	} ki_obj;
 
 	__u64			ki_user_data;	/* user's data for completion */
@@ -64,13 +63,11 @@ static inline void init_sync_kiocb(struct kiocb *kiocb, struct file *filp)
 	*kiocb = (struct kiocb) {
 			.ki_ctx = NULL,
 			.ki_filp = filp,
-			.ki_obj.tsk = current,
 		};
 }
 
 /* prototypes */
 #ifdef CONFIG_AIO
-extern ssize_t wait_on_sync_kiocb(struct kiocb *iocb);
 extern void aio_complete(struct kiocb *iocb, long res, long res2);
 struct mm_struct;
 extern void exit_aio(struct mm_struct *mm);
@@ -78,7 +75,6 @@ extern long do_io_submit(aio_context_t ctx_id, long nr,
 			 struct iocb __user *__user *iocbpp, bool compat);
 void kiocb_set_cancel_fn(struct kiocb *req, kiocb_cancel_fn *cancel);
 #else
-static inline ssize_t wait_on_sync_kiocb(struct kiocb *iocb) { return 0; }
 static inline void aio_complete(struct kiocb *iocb, long res, long res2) { }
 struct mm_struct;
 static inline void exit_aio(struct mm_struct *mm) { }
diff --git a/net/socket.c b/net/socket.c
index a2c33a4..4032931 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -642,8 +642,7 @@ static int do_sock_sendmsg(struct socket *sock, struct msghdr *msg,
 	iocb.private = &siocb;
 	ret = nosec ? __sock_sendmsg_nosec(&iocb, sock, msg, size) :
 		      __sock_sendmsg(&iocb, sock, msg, size);
-	if (-EIOCBQUEUED == ret)
-		ret = wait_on_sync_kiocb(&iocb);
+	BUG_ON(-EIOCBQUEUED == ret);
 	return ret;
 }
 
@@ -785,8 +784,7 @@ int sock_recvmsg(struct socket *sock, struct msghdr *msg,
 	init_sync_kiocb(&iocb, NULL);
 	iocb.private = &siocb;
 	ret = __sock_recvmsg(&iocb, sock, msg, size, flags);
-	if (-EIOCBQUEUED == ret)
-		ret = wait_on_sync_kiocb(&iocb);
+	BUG_ON(-EIOCBQUEUED == ret);
 	return ret;
 }
 EXPORT_SYMBOL(sock_recvmsg);
@@ -801,8 +799,7 @@ static int sock_recvmsg_nosec(struct socket *sock, struct msghdr *msg,
 	init_sync_kiocb(&iocb, NULL);
 	iocb.private = &siocb;
 	ret = __sock_recvmsg_nosec(&iocb, sock, msg, size, flags);
-	if (-EIOCBQUEUED == ret)
-		ret = wait_on_sync_kiocb(&iocb);
+	BUG_ON(-EIOCBQUEUED == ret);
 	return ret;
 }
 
-- 
1.9.1