Re: [PATCH for 4.11] userfaultfd: report actual registered features in fdinfo

[Mike Rapoport <rppt@linux.vnet.ibm.com>]

Hello Andrea,

On Mon, Apr 03, 2017 at 06:30:34PM +0200, Andrea Arcangeli wrote:
> Hello Mike,
> 
> On Mon, Apr 03, 2017 at 06:10:24PM +0300, Mike Rapoport wrote:
> > Actually, I've found these details in /proc useful when I was experimenting
> > with checkpoint-restore of an application that uses userfaultfd. With
> > interface in /proc/<pid>/ we know exactly which process use userfaultfd and
> > can act appropriately.
> 
> You've to be somewhat serialized by other means though, because
> "exactly" has a limit with fdinfo. For example by the time read()
> returns, the uffd may have been closed already by the app (just the
> uffd isn't ->release()d yet as the last fput has yet to run, the
> fdinfo runs the last fput in such case). As long as you can cope with
> this and you've a stable fdinfo it's ok.
> 

Well, by the time CRIU checkpoints open file descriptors, the process is
already stopped, hence we are not racing with anything here.


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