On Thu, May 23, 2019 at 04:14:47PM +0200, Christian Brauner wrote:

On Thu, May 23, 2019 at 01:51:18PM +0200, Christian Brauner wrote:

quoted

On Wed, May 22, 2019 at 06:57:37PM +0200, Oleg Nesterov wrote:

quoted

On 05/22, Christian Brauner wrote:

quoted

+static struct file *pick_file(struct files_struct *files, unsigned fd)
 {
-	struct file *file;
+	struct file *file = NULL;
 	struct fdtable *fdt;
 
 	spin_lock(&files->file_lock);

@@ -632,15 +629,65 @@ int __close_fd(struct files_struct *files, unsigned fd)
 		goto out_unlock;
 	rcu_assign_pointer(fdt->fd[fd], NULL);
 	__put_unused_fd(files, fd);
-	spin_unlock(&files->file_lock);
-	return filp_close(file, files);
 
 out_unlock:
 	spin_unlock(&files->file_lock);
-	return -EBADF;
+	return file;

...

quoted

+int __close_range(struct files_struct *files, unsigned fd, unsigned max_fd)
+{
+	unsigned int cur_max;
+
+	if (fd > max_fd)
+		return -EINVAL;
+
+	rcu_read_lock();
+	cur_max = files_fdtable(files)->max_fds;
+	rcu_read_unlock();
+
+	/* cap to last valid index into fdtable */
+	if (max_fd >= cur_max)
+		max_fd = cur_max - 1;
+
+	while (fd <= max_fd) {
+		struct file *file;
+
+		file = pick_file(files, fd++);

Well, how about something like

	static unsigned int find_next_opened_fd(struct fdtable *fdt, unsigned start)
	{
		unsigned int maxfd = fdt->max_fds;
		unsigned int maxbit = maxfd / BITS_PER_LONG;
		unsigned int bitbit = start / BITS_PER_LONG;

		bitbit = find_next_bit(fdt->full_fds_bits, maxbit, bitbit) * BITS_PER_LONG;
		if (bitbit > maxfd)
			return maxfd;
		if (bitbit > start)
			start = bitbit;
		return find_next_bit(fdt->open_fds, maxfd, start);
	}

quoted

	unsigned close_next_fd(struct files_struct *files, unsigned start, unsigned maxfd)
	{
		unsigned fd;
		struct file *file;
		struct fdtable *fdt;
	
		spin_lock(&files->file_lock);
		fdt = files_fdtable(files);
		fd = find_next_opened_fd(fdt, start);
		if (fd >= fdt->max_fds || fd > maxfd) {
			fd = -1;
			goto out;
		}

		file = fdt->fd[fd];
		rcu_assign_pointer(fdt->fd[fd], NULL);
		__put_unused_fd(files, fd);
	out:
		spin_unlock(&files->file_lock);

		if (fd == -1u)
			return fd;

		filp_close(file, files);
		return fd + 1;
	}

Thanks, Oleg!

I kept it dumb and was about to reply that your solution introduces more
code when it seemed we wanted to keep this very simple for now.
But then I saw that find_next_opened_fd() already exists as
find_next_fd(). So it's actually not bad compared to what I sent in v1.
So - with some small tweaks (need to test it and all now) - how do we
feel about?:

That's obviously not correct atm but I'll send out a tweaked version in
a bit.

So given that we would really need another find_next_open_fd() I think
sticking to the simple cond_resched() version I sent before is better
for now until we see real-world performance issues.
I was however missing a test for close_range(fd, fd, 0) anyway so I'll
need to send a v2 with this test added.

Christian