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    SubjectRe: [PATCH 6/6] procfs: Kill the bkl in ioctl
    Date
    On Tuesday 30 March 2010, Frederic Weisbecker wrote:
    > On Tue, Mar 30, 2010 at 09:38:11AM +0300, Alexey Dobriyan wrote:
    > > On Tue, Mar 30, 2010 at 9:20 AM, Frederic Weisbecker <fweisbec@gmail.com> wrote:
    > > > --- a/fs/proc/inode.c
    > > > +++ b/fs/proc/inode.c
    > > > @@ -231,9 +231,9 @@ static long proc_reg_unlocked_ioctl(struct file *file, unsigned int cmd, unsigne
    > > > if (rv == -ENOIOCTLCMD)
    > > > rv = -EINVAL;
    > > > } else if (ioctl) {
    > > > - lock_kernel();
    > > > + WARN_ONCE(1, "Procfs ioctl handlers must use unlocked_ioctl, "
    > > > + "%pf will be called without the Bkl held\n", ioctl);
    > > > rv = ioctl(file->f_path.dentry->d_inode, file, cmd, arg);
    > > > - unlock_kernel();
    > >
    > > Then delete the branch.
    > > Or go through formal feature-removal procedure.
    >
    >
    > I thought about it. I even started to write something in this
    > feature-removal file but realized that I can't remove the
    > .ioctl() callback from file operations. We still need to check
    > the user hasn't made the mistake of implementing it.
    >
    > What I can plan as a feature removal, though, is to keep the warning
    > but don't actually call the ioctl.

    I believe we can actually remove ioctl from file_operations. The patch I did
    to convert all users to ".unlocked_ioctl = default_ioctl," should really catch
    all cases, and I think we can enforce this by renaming fops->ioctl to locked_ioctl
    or old_ioctl to make sure we didn't miss any, and then mandate that this one
    is only used when unlocked_ioctl is set to default_ioctl.

    I also remember going through procfs ioctl operations some time ago and finding
    exactly three users, which I believe are the same ones that Frederic found.

    Arnd


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