Re: FYI: mmap_sem OOM patch

Peter Zijlstra
2010-07-08T11:02:14Z

On Thu, 2010-07-08 at 19:57 +0900, KOSAKI Motohiro wrote:
> > On Thu, 2010-07-08 at 03:39 -0700, Michel Lespinasse wrote:
> > >
> > >
> > > One way to fix this is to have T4 wake from the oom queue and return an
> > > allocation failure instead of insisting on going oom itself when T1
> > > decides to take down the task.
> > >
> > > How would you have T4 figure out the deadlock situation ? T1 is taking down T2, not T4...
> >
> > If T2 and T4 share a mmap_sem they belong to the same process. OOM takes
> > down the whole process by sending around signals of sorts (SIGKILL?), so
> > if T4 gets a fatal signal while it is waiting to enter the oom thingy,
> > have it abort and return an allocation failure.
> >
> > That alloc failure (along with a pending fatal signal) will very likely
> > lead to the release of its mmap_sem (if not, there's more things to
> > cure).
> >
> > At which point the cycle is broken an stuff continues as it was
> > intended.
>
> Now, I've reread current code. I think mmotm already have this.

<snip code>

[ small note on that we really should kill __GFP_NOFAIL, its utter
deadlock potential ]

> Thought?

So either its not working or google never tried that code?