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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id f27sm2963616qkl.25.2019.08.16.05.19.06 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 16 Aug 2019 05:19:06 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hybCE-0001q2-67; Fri, 16 Aug 2019 09:19:06 -0300 Date: Fri, 16 Aug 2019 09:19:06 -0300 From: Jason Gunthorpe To: Michal Hocko Cc: LKML , linux-mm@kvack.org, DRI Development , Intel Graphics Development , Peter Zijlstra , Ingo Molnar , Andrew Morton , David Rientjes , Christian =?utf-8?B?S8O2bmln?= , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Masahiro Yamada , Wei Wang , Andy Shevchenko , Thomas Gleixner , Jann Horn , Feng Tang , Kees Cook , Randy Dunlap , Daniel Vetter Subject: Re: [PATCH 2/5] kernel.h: Add non_block_start/end() Message-ID: <20190816121906.GC5398@ziepe.ca> References: <20190815141219.GF21596@ziepe.ca> <20190815155950.GN9477@dhcp22.suse.cz> <20190815165631.GK21596@ziepe.ca> <20190815174207.GR9477@dhcp22.suse.cz> <20190815182448.GP21596@ziepe.ca> <20190815190525.GS9477@dhcp22.suse.cz> <20190815191810.GR21596@ziepe.ca> <20190815193526.GT9477@dhcp22.suse.cz> <20190815201323.GU21596@ziepe.ca> <20190816081029.GA27790@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190816081029.GA27790@dhcp22.suse.cz> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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