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:
> > On Wed, May 22, 2019 at 06:57:37PM +0200, Oleg Nesterov wrote:
> > > On 05/22, Christian Brauner wrote:
> > > >
> > > > +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;
> > >
> > > ...
> > >
> > > > +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);
> > > }
> >
> > >
> > > 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
