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From: Michal Hocko <mhocko@kernel.org>
To: Jason Gunthorpe <jgg@ziepe.ca>
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 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 21:35:26 +0200
Message-ID: <20190815193526.GT9477@dhcp22.suse.cz> (raw)
In-Reply-To: <20190815191810.GR21596@ziepe.ca>

On Thu 15-08-19 16:18:10, Jason Gunthorpe wrote:
> On Thu, Aug 15, 2019 at 09:05:25PM +0200, Michal Hocko wrote:
> 
> > This is what you claim and I am saying that fs_reclaim is about a
> > restricted reclaim context and it is an ugly hack. It has proven to
> > report false positives. Maybe it can be extended to a generic reclaim.
> > I haven't tried that. Do not aim to try it.
> 
> Okay, great, I think this has been very helpful, at least for me,
> thanks. I did not know fs_reclaim was so problematic, or the special
> cases about OOM 'reclaim'. 

I am happy that this is more clear now.

> On this patch, I have no general objection to enforcing drivers to be
> non-blocking, I'd just like to see it done with the existing lockdep
> can't sleep detection rather than inventing some new debugging for it.
> 
> I understand this means the debugging requires lockdep enabled and
> will not run in production, but I'm of the view that is OK and in line
> with general kernel practice.

Yes and I do agree with this in general.

> 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. So in other words
it is no different from any other function in the kernel that calls into
allocator. As the API is missing gfp context then I hope it is not
called from any restricted contexts (except from the oom which we have
!blockable for).

> Lockdep has
> complained on that in past due to fs_reclaim - how do you know if it
> is a false positive?

I would have to see the specific lockdep splat.
-- 
Michal Hocko
SUSE Labs


  reply index

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
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 [this message]
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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