Re: [RFC PATCH 0/5] userfaultfd: non-cooperative: syncronous events

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

Hi,

On Fri, Aug 11, 2017 at 09:46:29AM -0400, Blake Caldwell wrote:
> > On Tue, May 16, 2017 at 01:35:57PM +0300, Mike Rapoport wrote:
> > > Hi,
> > 
> > Any comments on this?
> > Shall I repost without the "RFC" prefix?
> > 
> I have a use case for this feature exactly like what you have described. The
> process should be suspended until the event has been handled. I would like
> to test this if there is a rebased patchset out there somewhere? I'm using
> 4.13.0_rc3 from
> https://kernel.googlesource.com/pub/scm/linux/kernel/git/andrea/aa.git
> 
> I wasn't able to apply the patches without heavy modification (mostly patch
> 3/5).

I don't have a version rebased on Andrea's tree, sorry.
 
> Thanks for the work on this.
> > > These patches add ability to generate userfaultfd events so that thier
> > > processing will be synchronized with the non-cooperative thread that
> > > caused the event.
> > >
> > > In the non-cooperative case userfaultfd resumes execution of the
> > > thread that caused an event when the notification is read() by the uffd
> > monitor.
> > > In some cases, like, for example, madvise(MADV_REMOVE), it might be
> > > desirable to keep the thread that caused the event suspended until the
> > > uffd monitor had the event handled.
> > >
> > > The first two patches just shuffle the code a bit to make subsequent
> > > changes easier.
> > > The patches 3 and 4 create some unification in the way the threads are
> > > queued into waitqueues either after page fault or after a
> > > non-cooperative event.
> > > The fifth patch extends the userfaultfd API with an implementation of
> > > UFFD_EVENT_REMOVE_SYNC that allows to keep the thread that triggered
> > > UFFD_EVENT_REMOVE until the uffd monitor would not wake it explicitly.
> > >
> > > Mike Rapoport (5):
> > >   userfaultfd: introduce userfault_init_waitqueue helper
> > >   userfaultfd: introduce userfaultfd_should_wait helper
> > >   userfaultfd: non-cooperative: generalize wake key structure
> > >   userfaultfd: non-cooperative: use fault_pending_wqh for all events
> > >   userfaultfd: non-cooperative: allow synchronous EVENT_REMOVE
> > >
> > >  fs/userfaultfd.c                 | 205
> ++++++++++++++++++++++++---------------
> > >  include/uapi/linux/userfaultfd.h |  11 +++
> > >  2 files changed, 136 insertions(+), 80 deletions(-)
> > >
> > > --
> > > 2.7.4
> > >
> > 
> > --
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> 

-- 
Sincerely yours,
Mike.

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