Commit 8924feff authored by Al Viro's avatar Al Viro
Browse files

splice: lift pipe_lock out of splice_to_pipe() 



* splice_to_pipe() stops at pipe overflow and does *not* take pipe_lock
* ->splice_read() instances do the same
* vmsplice_to_pipe() and do_splice() (ultimate callers of splice_to_pipe())
  arrange for waiting, looping, etc. themselves.

That should make pipe_lock the outermost one.

Unfortunately, existing rules for the amount passed by vmsplice_to_pipe()
and do_splice() are quite ugly _and_ userland code can be easily broken
by changing those.  It's not even "no more than the maximal capacity of
this pipe" - it's "once we'd fed pipe->nr_buffers pages into the pipe,
leave instead of waiting".

Considering how poorly these rules are documented, let's try "wait for some
space to appear, unless given SPLICE_F_NONBLOCK, then push into pipe
and if we run into overflow, we are done".

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent db85a9eb

fs/fuse/dev.c

+0 −2
Original line number Diff line number Diff line
@@ -1364,7 +1364,6 @@ static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos, 
		goto out;



	ret = 0;

	pipe_lock(pipe);



	if (!pipe->readers) {

		send_sig(SIGPIPE, current, 0);
@@ -1400,7 +1399,6 @@ static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos, 
	}



out_unlock:

	pipe_unlock(pipe);



	if (do_wakeup) {

		smp_mb();

fs/splice.c

+58 −71
Original line number Diff line number Diff line
@@ -183,26 +183,18 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe, 
		       struct splice_pipe_desc *spd)

{

	unsigned int spd_pages = spd->nr_pages;

	int ret, do_wakeup, page_nr;

	int ret = 0, page_nr = 0;



	if (!spd_pages)

		return 0;



	ret = 0;

	do_wakeup = 0;

	page_nr = 0;



	pipe_lock(pipe);



	for (;;) {

		if (!pipe->readers) {

	if (unlikely(!pipe->readers)) {

		send_sig(SIGPIPE, current, 0);

			if (!ret)

		ret = -EPIPE;

			break;

		goto out;

	}



		if (pipe->nrbufs < pipe->buffers) {

	while (pipe->nrbufs < pipe->buffers) {

		int newbuf = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);

		struct pipe_buffer *buf = pipe->bufs + newbuf;
@@ -218,44 +210,14 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe, 
		page_nr++;

		ret += buf->len;



			if (pipe->files)

				do_wakeup = 1;



		if (!--spd->nr_pages)

				break;

			if (pipe->nrbufs < pipe->buffers)

				continue;



			break;

	}



		if (spd->flags & SPLICE_F_NONBLOCK) {

	if (!ret)

		ret = -EAGAIN;

			break;

		}



		if (signal_pending(current)) {

			if (!ret)

				ret = -ERESTARTSYS;

			break;

		}



		if (do_wakeup) {

			wakeup_pipe_readers(pipe);

			do_wakeup = 0;

		}



		pipe->waiting_writers++;

		pipe_wait(pipe);

		pipe->waiting_writers--;

	}



	pipe_unlock(pipe);



	if (do_wakeup)

		wakeup_pipe_readers(pipe);



out:

	while (page_nr < spd_pages)

		spd->spd_release(spd, page_nr++);
@@ -1339,6 +1301,20 @@ long do_splice_direct(struct file *in, loff_t *ppos, struct file *out, 
}

EXPORT_SYMBOL(do_splice_direct);



static int wait_for_space(struct pipe_inode_info *pipe, unsigned flags)

{

	while (pipe->nrbufs == pipe->buffers) {

		if (flags & SPLICE_F_NONBLOCK)

			return -EAGAIN;

		if (signal_pending(current))

			return -ERESTARTSYS;

		pipe->waiting_writers++;

		pipe_wait(pipe);

		pipe->waiting_writers--;

	}

	return 0;

}



static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,

			       struct pipe_inode_info *opipe,

			       size_t len, unsigned int flags);
@@ -1421,8 +1397,13 @@ static long do_splice(struct file *in, loff_t __user *off_in, 
			offset = in->f_pos;

		}



		pipe_lock(opipe);

		ret = wait_for_space(opipe, flags);

		if (!ret)

			ret = do_splice_to(in, &offset, opipe, len, flags);



		pipe_unlock(opipe);

		if (ret > 0)

			wakeup_pipe_readers(opipe);

		if (!off_in)

			in->f_pos = offset;

		else if (copy_to_user(off_in, &offset, sizeof(loff_t)))
@@ -1546,6 +1527,9 @@ static long vmsplice_to_pipe(struct file *file, const struct iovec __user *uiov, 
		return -ENOMEM;

	}



	pipe_lock(pipe);

	ret = wait_for_space(pipe, flags);

	if (!ret) {

		spd.nr_pages = get_iovec_page_array(&from, spd.pages,

						    spd.partial,

						    spd.nr_pages_max);
@@ -1553,7 +1537,10 @@ static long vmsplice_to_pipe(struct file *file, const struct iovec __user *uiov, 
			ret = spd.nr_pages;

		else

			ret = splice_to_pipe(pipe, &spd);



	}

	pipe_unlock(pipe);

	if (ret > 0)

		wakeup_pipe_readers(pipe);

	splice_shrink_spd(&spd);

	kfree(iov);

	return ret;

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