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Message-Id: <20190814134558.fe659b1a9a169c0150c3e57c@linux-foundation.org>
Date: Wed, 14 Aug 2019 13:45:58 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Daniel Vetter <daniel.vetter@...ll.ch>
Cc: LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
DRI Development <dri-devel@...ts.freedesktop.org>,
Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
Jason Gunthorpe <jgg@...pe.ca>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>, Michal Hocko <mhocko@...e.com>,
David Rientjes <rientjes@...gle.com>,
Christian König <christian.koenig@....com>,
Jérôme Glisse
<jglisse@...hat.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
Wei Wang <wvw@...gle.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>,
Jann Horn <jannh@...gle.com>, Feng Tang <feng.tang@...el.com>,
Kees Cook <keescook@...omium.org>,
Randy Dunlap <rdunlap@...radead.org>,
Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH 2/5] kernel.h: Add non_block_start/end()
On Wed, 14 Aug 2019 22:20:24 +0200 Daniel Vetter <daniel.vetter@...ll.ch> wrote:
> In some special cases we must not block, but there's not a
> spinlock, preempt-off, irqs-off or similar critical section already
> that arms the might_sleep() debug checks. Add a non_block_start/end()
> pair to annotate these.
>
> This will be used in the oom paths of mmu-notifiers, where blocking is
> not allowed to make sure there's forward progress. Quoting Michal:
>
> "The notifier is called from quite a restricted context - oom_reaper -
> which shouldn't depend on any locks or sleepable conditionals. The code
> should be swift as well but we mostly do care about it to make a forward
> progress. Checking for sleepable context is the best thing we could come
> up with that would describe these demands at least partially."
>
> Peter also asked whether we want to catch spinlocks on top, but Michal
> said those are less of a problem because spinlocks can't have an
> indirect dependency upon the page allocator and hence close the loop
> with the oom reaper.
I continue to struggle with this. It introduces a new kernel state
"running preemptibly but must not call schedule()". How does this make
any sense?
Perhaps a much, much more detailed description of the oom_reaper
situation would help out.
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