Hi, Dave
On 2020/1/16 上午12:43, Dave Jiang wrote:
On 1/15/20 4:18 AM, zhangfei wrote:
Hi, Greg
On 2020/1/14 下午10:59, Greg Kroah-Hartman wrote:
On Mon, Jan 13, 2020 at 11:34:55AM +0800, zhangfei wrote:
Hi, Greg
Thanks for the review.
On 2020/1/12 上午3:40, Greg Kroah-Hartman wrote:
On Sat, Jan 11, 2020 at 10:48:37AM +0800, Zhangfei Gao wrote:
+static int uacce_fops_open(struct inode *inode, struct file *filep)
+{
+ struct uacce_mm *uacce_mm = NULL;
+ struct uacce_device *uacce;
+ struct uacce_queue *q;
+ int ret = 0;
+
+ uacce = xa_load(&uacce_xa, iminor(inode));
+ if (!uacce)
+ return -ENODEV;
+
+ if (!try_module_get(uacce->parent->driver->owner))
+ return -ENODEV;
Why are you trying to grab the module reference of the parent device?
Why is that needed and what is that going to help with here?
This shouldn't be needed as the module reference of the owner of the
fileops for this module is incremented, and the "parent" module
depends
on this module, so how could it be unloaded without this code being
unloaded?
Yes, if you build this code into the kernel and the "parent"
driver is a
module, then you will not have a reference, but when you remove that
parent driver the device will be removed as it has to be unregistered
before that parent driver can be removed from the system, right?
Or what am I missing here?
The refcount here is preventing rmmod "parent" module after fd is
opened,
since user driver has mmap kernel memory to user space, like mmio,
which may
still in-use.
With the refcount protection, rmmod "parent" module will fail until
application free the fd.
log like: rmmod: ERROR: Module hisi_zip is in use
But if the "parent" module is to be unloaded, it has to unregister the
"child" device and that will call the destructor in here and then you
will tear everything down and all should be good.
There's no need to "forbid" a module from being unloaded, even if it is
being used. Look at all networking drivers, they work that way, right?
Thanks Greg for the kind suggestion.
I still have one uncertainty.
Does uacce has to block process continue accessing the mmapped area
when remove "parent" module?
Uacce can block device access the physical memory when parent module
call uacce_remove.
But application is still running, and suppose it is not the kernel
driver's responsibility to call unmap.
I am looking for some examples in kernel,
looks vfio does not block process continue accessing when
vfio_unregister_iommu_driver either.
In my test, application will keep waiting after rmmod parent, until
ctrl+c, when unmap is called.
During the process, kernel does not report any error.
Do you have any advice?
Would it work to call unmap_mapping_range() on the char dev
inode->i_mappings? I think you need to set the vma->fault function ptr
for the vm_operations_struct in the original mmap(). After the
mappings are unmapped, you can set a state variable to trigger the
return of VM_FAULT_SIGBUS in the ->fault function when the user app
accesses the mmap region again and triggers a page fault. The user app
needs to be programmed to catch exceptions to deal with that.
Thanks Dave for the advice.
Will look into it, may need some time to investigate.
I would like to make an additional patch for this issue, since it does
not impact the main function.
Thanks
