Re: [PATCH v4 4/5] cramfs: add mmap support

[Richard Weinberger]

On Mon, Oct 2, 2017 at 12:29 AM, Nicolas Pitre <nicolas.pitre@xxxxxxxxxx> wrote:
> On Sun, 1 Oct 2017, Christoph Hellwig wrote:
>
>> up_read(&mm->mmap_sem) in the fault path is a still a complete
>> no-go,
>>
>> NAK
>
> Care to elaborate?
>
> What about mm/filemap.c:__lock_page_or_retry() then?

As soon you up_read() in the page fault path other tasks will race
with you before
you're able to grab the write lock.

HTH

-- 
Thanks,
//richard