From: Jason Gunthorpe <jgg@ziepe.ca>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: "Michal Hocko" <mhocko@kernel.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
"Linux MM" <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>,
"David Rientjes" <rientjes@google.com>,
"Christian König" <christian.koenig@amd.com>,
"Jérôme 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@intel.com>
Subject: Re: [PATCH 2/5] kernel.h: Add non_block_start/end()
Date: Thu, 15 Aug 2019 11:37:59 -0300 [thread overview]
Message-ID: <20190815143759.GG21596@ziepe.ca> (raw)
In-Reply-To: <CAKMK7uE9zdmBuvxa788ONYky=46GN=5Up34mKDmsJMkir4x7MQ@mail.gmail.com>
On Thu, Aug 15, 2019 at 03:12:11PM +0200, Daniel Vetter wrote:
> On Thu, Aug 15, 2019 at 3:04 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> >
> > On Thu, Aug 15, 2019 at 10:44:29AM +0200, Michal Hocko wrote:
> >
> > > As the oom reaper is the primary guarantee of the oom handling forward
> > > progress it cannot be blocked on anything that might depend on blockable
> > > memory allocations. These are not really easy to track because they
> > > might be indirect - e.g. notifier blocks on a lock which other context
> > > holds while allocating memory or waiting for a flusher that needs memory
> > > to perform its work.
> >
> > But lockdep *does* track all this and fs_reclaim_acquire() was created
> > to solve exactly this problem.
> >
> > fs_reclaim is a lock and it flows through all the usual lockdep
> > schemes like any other lock. Any time the page allocator wants to do
> > something the would deadlock with reclaim it takes the lock.
> >
> > Failure is expressed by a deadlock cycle in the lockdep map, and
> > lockdep can handle arbitary complexity through layers of locks, work
> > queues, threads, etc.
> >
> > What is missing?
>
> Lockdep doens't seen everything by far. E.g. a wait_event will be
> caught by the annotations here, but not by lockdep.
Sure, but the wait_event might be OK if its progress isn't contingent
on fs_reclaim, ie triggered from interrupt, so why ban it?
> And since we're talking about mmu notifiers here and gpus/dma engines.
> We have dma_fence_wait, which can wait for any hw/driver in the system
> that takes part in shared/zero-copy buffer processing. Which at least
> on the graphics side is everything. This pulls in enormous amounts of
> deadlock potential that lockdep simply is blind about and will never
> see.
It seems very risky to entagle a notifier widely like that.
It looks pretty sure that notifiers are fs_reclaim, so at a minimum
that wait_event can't be contingent on anything that is doing
GFP_KERNEL or it will deadlock - and blockable doesn't make that sleep
safe.
Avoiding an uncertain wait_event under notifiers would seem to be the
only reasonable design here..
Jason
next prev parent reply other threads:[~2019-08-15 14:38 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-14 20:20 [PATCH 0/5] hmm & mmu_notifier debug/lockdep annotations Daniel Vetter
2019-08-14 20:20 ` [PATCH 1/5] mm: Check if mmu notifier callbacks are allowed to fail Daniel Vetter
2019-08-14 22:14 ` Andrew Morton
2019-08-14 23:22 ` Jason Gunthorpe
2019-08-14 23:34 ` Ralph Campbell
2019-08-16 17:19 ` Jason Gunthorpe
2019-08-14 20:20 ` [PATCH 2/5] kernel.h: Add non_block_start/end() Daniel Vetter
2019-08-14 20:45 ` Andrew Morton
2019-08-15 6:52 ` Daniel Vetter
2019-08-15 8:44 ` Michal Hocko
2019-08-15 13:04 ` Jason Gunthorpe
2019-08-15 13:12 ` Daniel Vetter
2019-08-15 14:37 ` Jason Gunthorpe [this message]
2019-08-15 14:43 ` Daniel Vetter
2019-08-15 15:10 ` Jason Gunthorpe
2019-08-15 16:25 ` Daniel Vetter
2019-08-15 17:35 ` Jason Gunthorpe
2019-08-15 17:39 ` Jerome Glisse
2019-08-15 18:01 ` Jason Gunthorpe
2019-08-15 18:27 ` Jerome Glisse
2019-08-15 18:57 ` Jason Gunthorpe
2019-08-15 16:32 ` Jerome Glisse
2019-08-15 17:16 ` Jason Gunthorpe
2019-08-15 17:21 ` Daniel Vetter
2019-08-15 17:35 ` Jerome Glisse
2019-08-15 13:24 ` Michal Hocko
2019-08-15 22:15 ` Andrew Morton
2019-08-16 8:24 ` Michal Hocko
2019-08-14 23:58 ` Jason Gunthorpe
2019-08-15 6:58 ` Daniel Vetter
2019-08-15 12:23 ` Jason Gunthorpe
2019-08-15 13:21 ` Michal Hocko
2019-08-15 14:12 ` Jason Gunthorpe
2019-08-15 16:00 ` Michal Hocko
2019-08-15 16:56 ` Jason Gunthorpe
2019-08-15 17:11 ` Jerome Glisse
2019-08-15 17:17 ` Jason Gunthorpe
2019-08-15 17:42 ` Michal Hocko
2019-08-15 17:57 ` Jerome Glisse
2019-08-15 18:24 ` Jason Gunthorpe
2019-08-15 19:05 ` Michal Hocko
2019-08-15 19:18 ` Jason Gunthorpe
2019-08-15 19:35 ` Michal Hocko
2019-08-15 20:13 ` Jason Gunthorpe
2019-08-16 8:10 ` Michal Hocko
2019-08-16 12:19 ` Jason Gunthorpe
2019-08-16 12:26 ` Michal Hocko
2019-08-15 20:16 ` [Intel-gfx] " Daniel Vetter
2019-08-15 20:27 ` Jason Gunthorpe
2019-08-15 20:49 ` Daniel Vetter
2019-08-16 1:00 ` Jason Gunthorpe
2019-08-16 6:20 ` Daniel Vetter
2019-08-16 12:12 ` Jason Gunthorpe
2019-08-16 14:11 ` Daniel Vetter
2019-08-16 14:38 ` Jason Gunthorpe
2019-08-16 16:36 ` Daniel Vetter
2019-08-16 16:54 ` Jason Gunthorpe
2019-08-16 8:27 ` Michal Hocko
2019-08-14 20:20 ` [PATCH 3/5] mm, notifier: Catch sleeping/blocking for !blockable Daniel Vetter
2019-08-15 0:00 ` Jason Gunthorpe
2019-08-15 7:02 ` Daniel Vetter
[not found] ` <20190815123556.GB21596@ziepe.ca>
2019-08-17 16:09 ` Daniel Vetter
2019-08-14 20:20 ` [PATCH 4/5] mm, notifier: Add a lockdep map for invalidate_range_start Daniel Vetter
2019-08-15 0:09 ` Jason Gunthorpe
2019-08-15 7:10 ` Daniel Vetter
2019-08-15 12:53 ` Jason Gunthorpe
2019-08-14 20:20 ` [PATCH 5/5] mm/hmm: WARN on illegal ->sync_cpu_device_pagetables errors Daniel Vetter
2019-08-15 0:11 ` Jason Gunthorpe
2019-08-15 7:14 ` Daniel Vetter
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