From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jason Gunthorpe <jgg@ziepe.ca>
Subject: Re: [PATCH 2/5] kernel.h: Add non_block_start/end()
Date: Fri, 16 Aug 2019 09:19:06 -0300
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To: Michal Hocko <mhocko@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org, DRI Development <dri-devel@lists.freedesktop.org>, Intel Graphics Development <intel-gfx@lists.freedesktop.org>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, David Rientjes <rientjes@google.com>, Christian =?utf-8?B?S8O2bmln?= <christian.koenig@amd.com>, =?utf-8?B?SsOpcsO0bWU=?= Glisse <jglisse@redhat.com>, Masahiro Yamada <yamada.masahiro@socionext.com>, Wei Wang <wvw@google.com>, Andy Shevchenko <andriy.shevchenko@linux.intel.com>, Thomas Gleixner <tglx@linutronix.de>, Jann Horn <jannh@google.com>, Feng Tang <feng.tang@intel.com>, Kees Cook <keescook@chromium.org>, Randy Dunlap <rdunlap@infradead.org>, Daniel Vetter <daniel.vetter@i>
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On Fri, Aug 16, 2019 at 10:10:29AM +0200, Michal Hocko wrote:
> On Thu 15-08-19 17:13:23, Jason Gunthorpe wrote:
> > On Thu, Aug 15, 2019 at 09:35:26PM +0200, Michal Hocko wrote:
> > 
> > > > The last detail is I'm still unclear what a GFP flags a blockable
> > > > invalidate_range_start() should use. Is GFP_KERNEL OK?
> > > 
> > > I hope I will not make this muddy again ;)
> > > invalidate_range_start in the blockable mode can use/depend on any sleepable
> > > allocation allowed in the context it is called from. 
> > 
> > 'in the context is is called from' is the magic phrase, as
> > invalidate_range_start is called while holding several different mm
> > related locks. I know at least write mmap_sem and i_mmap_rwsem
> > (write?)
> > 
> > Can GFP_KERNEL be called while holding those locks?
> 
> i_mmap_rwsem would be problematic because it is taken during the
> reclaim.

Okay.. So the fs_reclaim debugging does catch errors. Do you have any
reference for what a false positive looks like? 

I would like to inject it into the notifier path as this is very
difficult for driver authors to discover and know about, but I'm
worried about your false positive remark.

I think I understand we can use only GFP_ATOMIC in the notifiers, but
we need a strategy to handle OOM to guarentee forward progress.

This is just more bugs to fix :(

Jason