Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

Oleg Nesterov
2012-02-15T19:14:13Z

On 02/15, Cyrill Gorcunov wrote:
>
> On Wed, Feb 15, 2012 at 07:10:08PM +0400, Cyrill Gorcunov wrote:
> > On Wed, Feb 15, 2012 at 03:36:06PM +0100, Oleg Nesterov wrote:
> > >
> > > task->files can be NULL, we can race with exit_files().
> >
> > So I need to call get_files_struct. Thanks Oleg!
> >
>
> Something like below I think, right? (it seems this
> patc doesn't hit lenux-next yet, so here is interdiff
> output)
>
> Cyrill
> ---
> diff -u linux-2.6.git/kernel/kcmp.c linux-2.6.git/kernel/kcmp.c
> --- linux-2.6.git/kernel/kcmp.c
> +++ linux-2.6.git/kernel/kcmp.c
> @@ -44,16 +44,25 @@
> static struct file *
> get_file_raw_ptr(struct task_struct *task, unsigned int idx)
> {
> + struct files_struct *files;
> struct fdtable *fdt;
> struct file *file;
>
> - spin_lock(&task->files->file_lock);
> - fdt = files_fdtable(task->files);
> + files = get_files_struct(task);
> + if (!files)
> + return NULL;
> +
> + rcu_read_lock();
> +
> + fdt = files_fdtable(files);
> if (idx < fdt->max_fds)
> file = fdt->fd[idx];
> else
> file = NULL;
> - spin_unlock(&task->files->file_lock);
> +
> + rcu_read_unlock();
> +
> + put_files_struct(files);

I think this should work. Or you can simply do

struct file *file = NULL;

task_lock(task);
rcu_read_lock();
if (task->files)
file = fcheck_files(task->files, idx);
rcu_read_unlock();
task_unlock(task);

Oleg.