Re: [Xen-devel] [PATCH] mm, oom: distinguish blockable mode for mmu notifiers

[Michal Hocko <mhocko@xxxxxxxxxx>]

On Fri 24-08-18 15:10:08, Christian König wrote:
> Am 24.08.2018 um 15:01 schrieb Michal Hocko:
> > On Fri 24-08-18 14:52:26, Christian König wrote:
> > > Am 24.08.2018 um 14:33 schrieb Michal Hocko:
> > [...]
> > > > Thiking about it some more, I can imagine that a notifier callback which
> > > > performs an allocation might trigger a memory reclaim and that in turn
> > > > might trigger a notifier to be invoked and recurse. But notifier
> > > > shouldn't really allocate memory. They are called from deep MM code
> > > > paths and this would be extremely deadlock prone. Maybe Jerome can come
> > > > up some more realistic scenario. If not then I would propose to simplify
> > > > the locking here. We have lockdep to catch self deadlocks and it is
> > > > always better to handle a specific issue rather than having a code
> > > > without a clear indication how it can recurse.
> > > Well I agree that we should probably fix that, but I have some concerns to
> > > remove the existing workaround.
> > > 
> > > See we added that to get rid of a real problem in a customer environment 
> > > and
> > > I don't want to that to show up again.
> > It would really help to know more about that case and fix it properly
> > rather than workaround it like this. Anyway, let me think how to handle
> > the non-blocking notifier invocation then. I was not able to come up
> > with anything remotely sane yet.
> 
> With avoiding allocating memory in the write lock path I don't see an issue
> any more with that.
> 
> All what the write lock path does now is adding items to a linked lists,
> arrays etc....

Can we change it to non-sleepable lock then?
-- 
Michal Hocko
SUSE Labs

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