Re: mmap sync issue

[Michel Lespinasse <walken@google.com>]

On Sat, Mar 16, 2013 at 4:39 PM, Will Huck <will.huckk@gmail.com> wrote:
> On 03/15/2013 07:39 PM, Gil Weber wrote:
>> I am experiencing an issue with my device driver. I am using mmap and
>> ioctl to share information with my user space application.
>> The thing is that the shared memory does not seems to be synced. Do check
>> this, I have done a simple test:

So if I got this right, the issue is that the vmalloc_area is
virtually aliased between the kernel and the user space mapping, so
that coherency is not guaranteed on architectures that use virtually
aliased caches.

fs/aio.c does something similar to what you want with their ring
buffer. The kernel doesn't access the ring buffer through a vmalloc
area like you're trying to do; instead it uses kmap_atomic() ..
kunmap_atomic() whenever it wants to access it.

I don't actually consider myself an expert in this area but I believe
the above should solve your problem :)

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.

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