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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id d123sm1160617qkb.94.2019.06.07.07.03.13 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 07 Jun 2019 07:03:13 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hZFSb-0003fn-4v; Fri, 07 Jun 2019 11:03:13 -0300 Date: Fri, 7 Jun 2019 11:03:13 -0300 From: Jason Gunthorpe To: John Hubbard Cc: Jerome Glisse , Ralph Campbell , Felix.Kuehling@amd.com, linux-rdma@vger.kernel.org, linux-mm@kvack.org, Andrea Arcangeli , dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org Subject: Re: [PATCH v2 hmm 09/11] mm/hmm: Poison hmm_range during unregister Message-ID: <20190607140313.GI14802@ziepe.ca> References: <20190606184438.31646-1-jgg@ziepe.ca> <20190606184438.31646-10-jgg@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) 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 Thu, Jun 06, 2019 at 08:37:42PM -0700, John Hubbard wrote: > On 6/6/19 11:44 AM, Jason Gunthorpe wrote: > > From: Jason Gunthorpe > > > > Trying to misuse a range outside its lifetime is a kernel bug. Use WARN_ON > > and poison bytes to detect this condition. > > > > Signed-off-by: Jason Gunthorpe > > Reviewed-by: Jérôme Glisse > > v2 > > - Keep range start/end valid after unregistration (Jerome) > > mm/hmm.c | 7 +++++-- > > 1 file changed, 5 insertions(+), 2 deletions(-) > > > > diff --git a/mm/hmm.c b/mm/hmm.c > > index 6802de7080d172..c2fecb3ecb11e1 100644 > > +++ b/mm/hmm.c > > @@ -937,7 +937,7 @@ void hmm_range_unregister(struct hmm_range *range) > > struct hmm *hmm = range->hmm; > > > > /* Sanity check this really should not happen. */ > > That comment can also be deleted, as it has the same meaning as > the WARN_ON() that you just added. > > > - if (hmm == NULL || range->end <= range->start) > > + if (WARN_ON(range->end <= range->start)) > > return; > > > > mutex_lock(&hmm->lock); > > @@ -948,7 +948,10 @@ void hmm_range_unregister(struct hmm_range *range) > > range->valid = false; > > mmput(hmm->mm); > > hmm_put(hmm); > > - range->hmm = NULL; > > + > > + /* The range is now invalid, leave it poisoned. */ > > To be precise, we are poisoning the range's back pointer to it's > owning hmm instance. Maybe this is clearer: > > /* > * The range is now invalid, so poison it's hmm pointer. > * Leave other range-> fields in place, for the caller's use. > */ > > ...or something like that? > > > + range->valid = false; > > + memset(&range->hmm, POISON_INUSE, sizeof(range->hmm)); > > } > > EXPORT_SYMBOL(hmm_range_unregister); > > > > > > The above are very minor documentation points, so: > > Reviewed-by: John Hubbard done thanks Jason