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SubjectRe: [PROPOSED PATCH] ATM refcount + firestream
On Fri, 27 Oct 2000, Andrew Morton wrote:

> Patrick van de Lageweg wrote:
> >
> > Hi all,
> >
> > Here is the second try for the atm refcount problem. I've made made
> > several enhancement over the previos patch. Can you take a look at it if
> > I've missed anything? (This time it also includes the driver for the
> > firestream card. That's why the patch is so large. It's gziped and
> > uuencoded).
>
> Patrick, I looked at the modules stuff and you do not
> appear to be actually _using_ it anywhere:
>
> bix:/home/morton> grep owner patch
> + owner: THIS_MODULE,
> + owner: THIS_MODULE
> + owner: THIS_MODULE,
> + owner: THIS_MODULE,
> + owner: THIS_MODULE,
> + owner: THIS_MODULE,
> + owner: THIS_MODULE,
> + struct module *owner;
> + struct module *owner;
> bix:/home/morton>

We use it throught the fops_get/fops_put macros to in/decrease the mod
counter. See the definitions for those macros (include/linux/fs.h)

Patrick
>
>
> It looks like you'll need something like the following:
> (warning: uncompiled ATM-ignoramus code)
>
> Index: net/atm/common.c
> ===================================================================
> RCS file: /opt/cvs/lk/net/atm/common.c,v
> retrieving revision 1.3.2.1
> diff -u -u -r1.3.2.1 common.c
> --- net/atm/common.c 2000/07/08 06:26:43 1.3.2.1
> +++ net/atm/common.c 2000/10/27 11:17:45
> @@ -144,6 +144,8 @@
> "rx_inuse == %d after closing\n",
> atomic_read(&vcc->rx_inuse));
> + if (vcc->dev->ops->owner)
> + __MOD_DEC_USE_COUNT(vcc->dev->ops->owner);
> bind_vcc(vcc,NULL);
> }
> if (free_sk) free_atm_vcc_sk(sk);
> }
> @@ -199,13 +201,22 @@
> {
> int error;
>
> + if (try_inc_mod_count(dev->ops->owner) == 0) {
> + return -ENODEV;
> + }
> +
> + error = 0;
> +
> if ((vpi != ATM_VPI_UNSPEC && vpi != ATM_VPI_ANY &&
> vpi >> dev->ci_range.vpi_bits) || (vci != ATM_VCI_UNSPEC &&
> - vci != ATM_VCI_ANY && vci >> dev->ci_range.vci_bits))
> - return -EINVAL;
> - if (vci > 0 && vci < ATM_NOT_RSV_VCI && !capable(CAP_NET_BIND_SERVICE))
> - return -EPERM;
> - error = 0;
> + vci != ATM_VCI_ANY && vci >> dev->ci_range.vci_bits)) {
> + error = -EINVAL;
> + goto out;
> + }
> + if (vci > 0 && vci < ATM_NOT_RSV_VCI && !capable(CAP_NET_BIND_SERVICE)) {
> + error = -EPERM;
> + goto out;
> + }
> bind_vcc(vcc,dev);
> switch (vcc->qos.aal) {
> case ATM_AAL0:
> @@ -231,19 +242,26 @@
> if (!error) error = adjust_tp(&vcc->qos.rxtp,vcc->qos.aal);
> if (error) {
> bind_vcc(vcc,NULL);
> - return error;
> + goto out;
> }
> DPRINTK("VCC %d.%d, AAL %d\n",vpi,vci,vcc->qos.aal);
> DPRINTK(" TX: %d, PCR %d..%d, SDU %d\n",vcc->qos.txtp.traffic_class,
> vcc->qos.txtp.min_pcr,vcc->qos.txtp.max_pcr,vcc->qos.txtp.max_sdu);
> DPRINTK(" RX: %d, PCR %d..%d, SDU %d\n",vcc->qos.rxtp.traffic_class,
> vcc->qos.rxtp.min_pcr,vcc->qos.rxtp.max_pcr,vcc->qos.rxtp.max_sdu);
> +
> if (dev->ops->open) {
> error = dev->ops->open(vcc,vpi,vci);
> if (error) {
> bind_vcc(vcc,NULL);
> - return error;
> + goto out;
> }
> + }
> +
> +out:
> + if (error) {
> + if (dev->ops->owner)
> + __MOD_DEC_USE_COUNT(dev->ops->owner);
> }
> return 0;
> }
>
>
> Something similar will be need to be wrapped around the usage of
> `struct atm_tcp_ops()' as well. Let me know if you'd like me to
> prototype a patch for that.
>
> The other thing you need to watch out for is atmdev_ops.ioctl().
> Can this be called when the device is not open?
>
> In other words, can atmdev_ops.ioctl() be called prior to
> atmdev_ops.open()? In more other words, can ioctl() be
> called after close()?
>
> If so then the above patch is not sufficient - it only increments
> the module use count on the open() path.
>
> If this is the case then you're fairly severely screwed. This is
> because the atm_dev handling has the same design flaw as the
> netdevice handling: the logical place to inc/dec the module
> refcount is within atm_dev_[de]register(). But this doesn't
> work because you can never _get_ to the deregister point
> through sys_delete_module() to drop the refcount.
>
> Like netdevices, ATM needs to be able to separate the act
> of loading the module from the act of registering the driver.
>
> netdevices manage to get away with it because of ANK's funky
> dev_hold()/dev_put() refcounting. It looks like ATM devices
> aren't that lucky.
>
> One workaround would be to refuse to allow the device to be
> accessed at all if it isn't open. This may be unacceptable.
>
>
> Look, this modules stuff is really bad. Phillip Rumpf proposed
> a radical alternative a while back which I felt was not given
> sufficient consideration. The idea was to make sys_delete_module()
> grab all the other CPUs and leave them spinning on a flag while
> the unload was proceeding. This was very similar to
> arch/i386/kernel/apm.c:apm_power_off().
>
> As far as I can recall, the only restriction was that you are
> not allowed to call module functions when the module refcount
> is zero if those functions can call schedule().
>
> prumpf, please dig out that patch.
>

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