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[79.181.91.42]) by smtp.gmail.com with ESMTPSA id b7sm18536990qtt.38.2019.07.23.03.42.41 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 23 Jul 2019 03:42:47 -0700 (PDT) Date: Tue, 23 Jul 2019 06:42:38 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: syzbot , aarcange@redhat.com, akpm@linux-foundation.org, christian@brauner.io, davem@davemloft.net, ebiederm@xmission.com, elena.reshetova@intel.com, guro@fb.com, hch@infradead.org, james.bottomley@hansenpartnership.com, jglisse@redhat.com, keescook@chromium.org, ldv@altlinux.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-parisc@vger.kernel.org, luto@amacapital.net, mhocko@suse.com, mingo@kernel.org, namit@vmware.com, peterz@infradead.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk, wad@chromium.org Subject: Re: WARNING in __mmdrop Message-ID: <20190723062842-mutt-send-email-mst@kernel.org> References: <0000000000008dd6bb058e006938@google.com> <000000000000964b0d058e1a0483@google.com> <20190721044615-mutt-send-email-mst@kernel.org> <75c43998-3a1c-676f-99ff-3d04663c3fcc@redhat.com> <20190722035657-mutt-send-email-mst@kernel.org> <20190723010156-mutt-send-email-mst@kernel.org> <124be1a2-1c53-8e65-0f06-ee2294710822@redhat.com> <20190723032800-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jul 23, 2019 at 04:42:19PM +0800, Jason Wang wrote: > > So how about this: do exactly what you propose but as a 2 patch series: > > start with the slow safe patch, and add then return uaddr optimizations > > on top. We can then more easily reason about whether they are safe. > > > If you stick, I can do this. So I definitely don't insist but I'd like us to get back to where we know existing code is very safe (if not super fast) and optimizing from there. Bugs happen but I'd like to see a bisect giving us "oh it's because of XYZ optimization" and not the general "it's somewhere within this driver" that we are getting now. Maybe the way to do this is to revert for this release cycle and target the next one. What do you think? -- MST