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[209.85.220.65]) by mx.google.com with SMTPS id w16sor1857088ljw.32.2019.06.07.12.33.33 for (Google Transport Security); Fri, 07 Jun 2019 12:33:33 -0700 (PDT) Received-SPF: pass (google.com: domain of jrdr.linux@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=WBAeb9Yr; spf=pass (google.com: domain of jrdr.linux@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=jrdr.linux@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=gEQTt/69w62CAMJlx7lidr4JWqQ1JSVOKzZe9wzUYD0=; b=WBAeb9YrKbAluVQu4nrMlV3okf6XsP120P+h1v7Rd4vr3vsnkTU4vgCpduY2YM5ezQ ZC8U/tNgH2EZA0xU6gYm6T8EHUBJFtOyB8pCUYpNHE0K2uu7cRS2HajdLzZVPGJNWmLP o5kn20ai9Nk6v1lhHpA15tdkXrTIPHbeu1KGol63jaJ85T1QmQKpgRq8dBfivro5TDq/ 0VVuFLvOpVZ30wfG4maqWRq7WEpWaiwNYozzr3KF2QYpm6e3SiLKwMCnouJNlEACXYDG /DhWUWfy9Gpre3kK/XzwNxujrgejdBj3ZDHJ4T5DTjCnGMOJBfhZFptCx2FUne4MeKwM KqOA== X-Google-Smtp-Source: APXvYqyV5At9/bNoRANbxY42yFL3bcvziWxc6FqbPzzHMOEDWF48b73ld+sfmXEOlH6jYmy6qcg6bXlVtdgv8tNf/9Q= X-Received: by 2002:a2e:8696:: with SMTP id l22mr5536229lji.201.1559936013206; Fri, 07 Jun 2019 12:33:33 -0700 (PDT) MIME-Version: 1.0 References: <20190523153436.19102-1-jgg@ziepe.ca> <20190523153436.19102-10-jgg@ziepe.ca> In-Reply-To: <20190523153436.19102-10-jgg@ziepe.ca> From: Souptick Joarder Date: Sat, 8 Jun 2019 01:08:37 +0530 Message-ID: Subject: Re: [RFC PATCH 09/11] mm/hmm: Remove racy protection against double-unregistration To: Jason Gunthorpe Cc: linux-rdma@vger.kernel.org, Linux-MM , Jerome Glisse , Ralph Campbell , John Hubbard , Jason Gunthorpe Content-Type: text/plain; charset="UTF-8" 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, May 23, 2019 at 9:05 PM Jason Gunthorpe wrote: > > From: Jason Gunthorpe > > No other register/unregister kernel API attempts to provide this kind of > protection as it is inherently racy, so just drop it. > > Callers should provide their own protection, it appears nouveau already > does, but just in case drop a debugging POISON. > > Signed-off-by: Jason Gunthorpe > --- > mm/hmm.c | 9 ++------- > 1 file changed, 2 insertions(+), 7 deletions(-) > > diff --git a/mm/hmm.c b/mm/hmm.c > index 46872306f922bb..6c3b7398672c29 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -286,18 +286,13 @@ EXPORT_SYMBOL(hmm_mirror_register); > */ > void hmm_mirror_unregister(struct hmm_mirror *mirror) > { > - struct hmm *hmm = READ_ONCE(mirror->hmm); > - > - if (hmm == NULL) > - return; > + struct hmm *hmm = mirror->hmm; How about remove struct hmm *hmm and replace the code like below - down_write(&mirror->hmm->mirrors_sem); list_del_init(&mirror->list); up_write(&mirror->hmm->mirrors_sem); hmm_put(hmm); memset(&mirror->hmm, POISON_INUSE, sizeof(mirror->hmm)); Similar to hmm_mirror_register(). > down_write(&hmm->mirrors_sem); > list_del_init(&mirror->list); > - /* To protect us against double unregister ... */ > - mirror->hmm = NULL; > up_write(&hmm->mirrors_sem); > - > hmm_put(hmm); > + memset(&mirror->hmm, POISON_INUSE, sizeof(mirror->hmm)); > } > EXPORT_SYMBOL(hmm_mirror_unregister); > > -- > 2.21.0 >