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    SubjectRe: [PATCH] generic_nvram: Turn nvram_ioctl into an unlocked ioctl
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    On Monday 12 October 2009, Frederic Weisbecker wrote:
    > nvram_ioctl is a bkl locked ioctl, but it can be an unlocked ioctl.
    >
    > - part is provided by the user
    > - offset is provided by pmac_get_partition() which is safe as it only
    > touches nvram_partitions, an array inistialized on __init time and
    > read-only the rest of the time.
    > - nvram_sync() only relies on core99_nvram_sync() which checks
    > is_core_99, nvram_data, nvram_image. Those are variables initialized
    > on __init time only and their direct values are not touched further.
    > The rest modifies the nvram image header, protected by nv_lock
    > already.
    >
    > So it's safe to call nvram_ioctl without the big kernel lock held.
    >
    > Reported-by: Arnd Bergmann <arndbergmann@googlemail.com>
    > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Cc: Ingo Molnar <mingo@elte.hu>
    > Cc: John Kacur <jkacur@redhat.com>
    > Cc: Sven-Thorsten Dietrich <sven@thebigcorporation.com>
    > Cc: Jonathan Corbet <corbet@lwn.net>
    > Cc: Alessio Igor Bogani <abogani@texware.it>
    > Cc: Arnd Bergmann <arndbergmann@googlemail.com>
    > Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>

    Hmm, I wish I had not started using the gmail MTA for sending out
    mail, not that address is public forever.

    > drivers/char/generic_nvram.c | 10 +++++-----
    > 1 files changed, 5 insertions(+), 5 deletions(-)
    >
    > diff --git a/drivers/char/generic_nvram.c b/drivers/char/generic_nvram.c
    > index c49200e..fd448aa 100644
    > --- a/drivers/char/generic_nvram.c
    > +++ b/drivers/char/generic_nvram.c
    > @@ -118,11 +118,11 @@ static int nvram_ioctl(struct inode *inode, struct file *file,
    > }
    >
    > const struct file_operations nvram_fops = {
    > - .owner = THIS_MODULE,
    > - .llseek = nvram_llseek,
    > - .read = read_nvram,
    > - .write = write_nvram,
    > - .ioctl = nvram_ioctl,
    > + .owner = THIS_MODULE,
    > + .llseek = nvram_llseek,
    > + .read = read_nvram,
    > + .write = write_nvram,
    > + .unlocked_ioctl = nvram_ioctl,
    > };
    >
    > static struct miscdevice nvram_dev = {

    The ioctl and unlocked_ioctl functions have a different signature, so you
    need to adapt that, not just rename it.

    Not sure if we should do it in the same patch, but this driver should also
    have a compat_ioctl method pointing to the same function. The ioctl numbers
    in this driver are all 32/64 bit clean, but are not listed in fs/compat_ioctl.c,
    so adding a .compat_ioctl pointer is the easiest way to fix 32 bit userland
    accessing the device.

    Arnd <><


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