Re: FYI: mmap_sem OOM patch

KOSAKI Motohiro
2010-07-08T11:06:59Z

> 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 ]

I disagree. __GFP_NOFAIL mean this allocation failure can makes really
dangerous result. Instead, OOM-Killer should try to kill next process.
I think.

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

Michel?