Re: mlockall and mmap of IO devices don't mix

[Andrew Morton <akpm@osdl.org>]

Joe Korty <joe.korty@ccur.com> wrote:
>
> On Fri, May 21, 2004 at 07:13:26PM -0700, Andrew Morton wrote:
>  > Mark Hounschell <markh@compro.net> wrote:
>  > >
>  > > Joe Korty wrote:
>  > > > 
>  > > > 2.6.0-test6: the use of mlockall(2) in a process that has mmap(2)ed
>  > > > the registers of an IO device will hang that process uninterruptibly.
>  > > > The task runs in an infinite loop in get_user_pages(), invoking
>  > > > follow_page() forever.
>  > > > 
>  > > > Using binary search I discovered that the problem was introduced
>  > > > in 2.5.14, specifically in ChangeSetKey
>  > > > 
>  > > >     zippel@linux-m68k.org|ChangeSet|20020503210330|37095
>  > > > 
>  > > 
>  > > I know this is an old thread but can anyone tell me if this problem is
>  > > resolved in the current 2.6.6 kernel? 
>  > > 
>  > 
>  > There's an utterly ancient patch in -mm which might fix this.
>  > 
>  > http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.6/2.6.6-mm4/broken-out/get_user_pages-handle-VM_IO.patch
> 
>  [ 2nd send -- corporate email system in the throes of being scrambled / updated ]
> 
>  Andrew,
>  I have been using this patch for ages.  Any chance of it being forwared to
>  the official tree?

That patch had its first birthday last week.  I wrote it in response to
some long-forgotten problem, failed to changelog it at the time then forgot
why I wrote it.  I kept it in the hope that I'd remember why I wrote it.  I
subsequently wrote a best-effort changelog but am unconvinced by it.  Ho
hum.

Let me genuflect a bit.  I guess we can be reasonably confident it won't
break anything.