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Subject[PATCH 1/4 v2] UIO: hold a reference to the device's owner while the device is open
Otherwise the device might just disappear while /dev/uioX is being used
which results in an Oops.

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
---
Hans J. Koch wrote:
> > > The label err_module_get should probably be omitted because it's used only
> > > once and has just one line of code. You could simply write "return ret"
> > > instead of "goto err_module_get".
> > This makes code shuffling easier. For example if someone decides that
> > try_module_get should be done after allocating listener then you only
> > have to exchange the two corresponding code blocks and the two groups
> > (label + cleanup) in the error handling block.
> > If the error handling is spread over the whole functions you can easily
> > miss something---as happend above. :-)
>
> Well, it depends. It's all about readability. Any function should be
> written in a way that makes it as clear as possible what it does. Your
> code is certainly not critical regarding that aspect, but I think it can
> still be improved. And a label that is used only once and contains only
> one line of code is definetly unnecessary. I don't follow the
> maybe-one-day-in-the-future-it-might-be-useful philosophy. I like code
> that is as clean and readable as possible _now_.
That thing about code reordering is minor compared to having all error
handling in one place, but ...

> And as this patch is
> not just a driver but affects the UIO core, this is even more important.
>
> Could you please send an updated patch?
... , it's your code, so you can find a new version below.

Best regards
Uwe

drivers/uio/uio.c | 36 +++++++++++++++++++++---------------
1 files changed, 21 insertions(+), 15 deletions(-)
diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 1175908..55cc7b8 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -301,23 +301,33 @@ static int uio_open(struct inode *inode, struct file *filep)
if (!idev)
return -ENODEV;

+ if (!try_module_get(idev->owner))
+ return -ENODEV;
+
listener = kmalloc(sizeof(*listener), GFP_KERNEL);
- if (!listener)
- return -ENOMEM;
+ if (!listener) {
+ ret = -ENOMEM;
+ goto err_alloc_listener;
+ }

listener->dev = idev;
listener->event_count = atomic_read(&idev->event);
filep->private_data = listener;

if (idev->info->open) {
- if (!try_module_get(idev->owner))
- return -ENODEV;
ret = idev->info->open(idev->info, inode);
- module_put(idev->owner);
+ if (ret)
+ goto err_infoopen;
}

- if (ret)
- kfree(listener);
+ return 0;
+
+err_infoopen:
+
+ kfree(listener);
+err_alloc_listener:
+
+ module_put(idev->owner);

return ret;
}
@@ -336,12 +346,11 @@ static int uio_release(struct inode *inode, struct file *filep)
struct uio_listener *listener = filep->private_data;
struct uio_device *idev = listener->dev;

- if (idev->info->release) {
- if (!try_module_get(idev->owner))
- return -ENODEV;
+ if (idev->info->release)
ret = idev->info->release(idev->info, inode);
- module_put(idev->owner);
- }
+
+ module_put(idev->owner);
+
if (filep->f_flags & FASYNC)
ret = uio_fasync(-1, filep, 0);
kfree(listener);
@@ -510,10 +519,7 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
return -EINVAL;

if (idev->info->mmap) {
- if (!try_module_get(idev->owner))
- return -ENODEV;
ret = idev->info->mmap(idev->info, vma);
- module_put(idev->owner);
return ret;
}

--
1.5.4.5

--
Uwe Kleine-König, Software Engineer
Digi International GmbH Branch Breisach, Küferstrasse 8, 79206 Breisach, Germany
Tax: 315/5781/0242 / VAT: DE153662976 / Reg. Amtsgericht Dortmund HRB 13962
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