Commit b2858d7d authored by Miklos Szeredi's avatar Miklos Szeredi Committed by Jens Axboe
Browse files

splice: fix kmaps in default_file_splice_write() 



Unfortunately multiple kmap() within a single thread are deadlockable,
so writing out multiple buffers with writev() isn't possible.

Change the implementation so that it does a separate write() for each
buffer.  This actually simplifies the code a lot since the
splice_from_pipe() helper can be used.

This limitation is caused by HIGHMEM pages, and so only affects a
subset of architectures and configurations.  In the future it may be
worth to implement default_file_splice_write() in a more efficient way
on configs that allow it.

Signed-off-by: default avatarMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 4fc981ef

fs/splice.c

+22 −108
Original line number Diff line number Diff line
@@ -535,8 +535,8 @@ static ssize_t kernel_readv(struct file *file, const struct iovec *vec, 
	return res;

}



static ssize_t kernel_writev(struct file *file, const struct iovec *vec,

			    unsigned long vlen, loff_t *ppos)

static ssize_t kernel_write(struct file *file, const char *buf, size_t count,

			    loff_t pos)

{

	mm_segment_t old_fs;

	ssize_t res;
@@ -544,7 +544,7 @@ static ssize_t kernel_writev(struct file *file, const struct iovec *vec, 
	old_fs = get_fs();

	set_fs(get_ds());

	/* The cast to a user pointer is valid due to the set_fs() */

	res = vfs_writev(file, (const struct iovec __user *)vec, vlen, ppos);

	res = vfs_write(file, (const char __user *)buf, count, &pos);

	set_fs(old_fs);



	return res;
@@ -1003,120 +1003,34 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out, 


EXPORT_SYMBOL(generic_file_splice_write);



static struct pipe_buffer *nth_pipe_buf(struct pipe_inode_info *pipe, int n)

{

	return &pipe->bufs[(pipe->curbuf + n) % PIPE_BUFFERS];

}



static ssize_t default_file_splice_write(struct pipe_inode_info *pipe,

					 struct file *out, loff_t *ppos,

					 size_t len, unsigned int flags)

static int write_pipe_buf(struct pipe_inode_info *pipe, struct pipe_buffer *buf,

			  struct splice_desc *sd)

{

	ssize_t ret = 0;

	ssize_t total_len = 0;

	int do_wakeup = 0;



	pipe_lock(pipe);

	while (len) {

		struct pipe_buffer *buf;

		void *data[PIPE_BUFFERS];

		struct iovec vec[PIPE_BUFFERS];

		unsigned int nr_pages = 0;

		unsigned int write_len = 0;

		unsigned int now_len = len;

		unsigned int this_len;

		int i;



		BUG_ON(pipe->nrbufs > PIPE_BUFFERS);

		for (i = 0; i < pipe->nrbufs && now_len; i++) {

			buf = nth_pipe_buf(pipe, i);

	int ret;

	void *data;



	ret = buf->ops->confirm(pipe, buf);

	if (ret)

				break;



			data[i] = buf->ops->map(pipe, buf, 0);

			this_len = min(buf->len, now_len);

			vec[i].iov_base = (void __user *) data[i] + buf->offset;

			vec[i].iov_len = this_len;

			now_len -= this_len;

			write_len += this_len;

			nr_pages++;

		}



		if (nr_pages) {

			ret = kernel_writev(out, vec, nr_pages, ppos);

			if (ret == 0)

				ret = -EIO;

			if (ret > 0) {

				len -= ret;

				total_len += ret;

			}

		}



		for (i = 0; i < nr_pages; i++) {

			buf = nth_pipe_buf(pipe, i);

			buf->ops->unmap(pipe, buf, data[i]);



			if (ret > 0) {

				this_len = min_t(unsigned, vec[i].iov_len, ret);

				buf->offset += this_len;

				buf->len -= this_len;

				ret -= this_len;

			}

		}



		if (ret < 0)

			break;



		while (pipe->nrbufs) {

			const struct pipe_buf_operations *ops;



			buf = nth_pipe_buf(pipe, 0);

			if (buf->len)

				break;



			ops = buf->ops;

			buf->ops = NULL;

			ops->release(pipe, buf);

			pipe->curbuf = (pipe->curbuf + 1) % PIPE_BUFFERS;

			pipe->nrbufs--;

			if (pipe->inode)

				do_wakeup = 1;

		}



		if (pipe->nrbufs)

			continue;

		if (!pipe->writers)

			break;

		if (!pipe->waiting_writers) {

			if (total_len)

				break;

		}



		if (flags & SPLICE_F_NONBLOCK) {

			ret = -EAGAIN;

			break;

		}

		return ret;



		if (signal_pending(current)) {

			ret = -ERESTARTSYS;

			break;

		}

	data = buf->ops->map(pipe, buf, 0);

	ret = kernel_write(sd->u.file, data + buf->offset, sd->len, sd->pos);

	buf->ops->unmap(pipe, buf, data);



		if (do_wakeup) {

			wakeup_pipe_writers(pipe);

			do_wakeup = 0;

	return ret;

}



		pipe_wait(pipe);

	}

	pipe_unlock(pipe);

static ssize_t default_file_splice_write(struct pipe_inode_info *pipe,

					 struct file *out, loff_t *ppos,

					 size_t len, unsigned int flags)

{

	ssize_t ret;



	if (do_wakeup)

		wakeup_pipe_writers(pipe);

	ret = splice_from_pipe(pipe, out, ppos, len, flags, write_pipe_buf);

	if (ret > 0)

		*ppos += ret;



	return total_len ? total_len : ret;

	return ret;

}



/**

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