From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yb0-f197.google.com (mail-yb0-f197.google.com [209.85.213.197]) by kanga.kvack.org (Postfix) with ESMTP id D468D6B000C for ; Mon, 26 Mar 2018 10:54:35 -0400 (EDT) Received: by mail-yb0-f197.google.com with SMTP id m3-v6so2661352ybk.19 for ; Mon, 26 Mar 2018 07:54:35 -0700 (PDT) Date: Mon, 26 Mar 2018 07:54:31 -0700 From: Tejun Heo Subject: Re: [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup Message-ID: <20180326145431.GC1840639@devbig577.frc2.facebook.com> References: <20180314194205.1651587-1-tj@kernel.org> <20180314194515.1661824-1-tj@kernel.org> <20180314194515.1661824-4-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180314194515.1661824-4-tj@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: security@kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, linux-mm@kvack.org, torvalds@linux-foundation.org, jannh@google.com, paulmck@linux.vnet.ibm.com, bcrl@kvack.org, viro@zeniv.linux.org.uk, kent.overstreet@gmail.com Hello, Andrew. Do you mind picking up the following patch? I can't find a good tree to route this through. The raw patch can be found at https://marc.info/?l=linux-mm&m=152105674112496&q=raw Thank you very much. On Wed, Mar 14, 2018 at 12:45:11PM -0700, Tejun Heo wrote: > hmm_devmem_find() requires rcu_read_lock_held() but there's nothing > which actually uses the RCU protection. The only caller is > hmm_devmem_pages_create() which already grabs the mutex and does > superflous rcu_read_lock/unlock() around the function. > > This doesn't add anything and just adds to confusion. Remove the RCU > protection and open-code the radix tree lookup. If this needs to > become more sophisticated in the future, let's add them back when > necessary. > > Signed-off-by: Tejun Heo > Reviewed-by: Jerome Glisse > Cc: linux-mm@kvack.org > Cc: Linus Torvalds > --- > Hello, > > Jerome, how do you want to route this patch? If you prefer, I can > route it together with other patches. > > Thanks. > > mm/hmm.c | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) > > diff --git a/mm/hmm.c b/mm/hmm.c > index 320545b98..d4627c5 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -845,13 +845,6 @@ static void hmm_devmem_release(struct device *dev, void *data) > hmm_devmem_radix_release(resource); > } > > -static struct hmm_devmem *hmm_devmem_find(resource_size_t phys) > -{ > - WARN_ON_ONCE(!rcu_read_lock_held()); > - > - return radix_tree_lookup(&hmm_devmem_radix, phys >> PA_SECTION_SHIFT); > -} > - > static int hmm_devmem_pages_create(struct hmm_devmem *devmem) > { > resource_size_t key, align_start, align_size, align_end; > @@ -892,9 +885,8 @@ static int hmm_devmem_pages_create(struct hmm_devmem *devmem) > for (key = align_start; key <= align_end; key += PA_SECTION_SIZE) { > struct hmm_devmem *dup; > > - rcu_read_lock(); > - dup = hmm_devmem_find(key); > - rcu_read_unlock(); > + dup = radix_tree_lookup(&hmm_devmem_radix, > + key >> PA_SECTION_SHIFT); > if (dup) { > dev_err(device, "%s: collides with mapping for %s\n", > __func__, dev_name(dup->device)); > -- > 2.9.5 > -- tejun From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-1197340-1522076080-2-16271515356625771943 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, RCVD_IN_DNSWL_HI -5, T_RP_MATCHES_RCVD -0.01, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='198.145.29.99', Host='mail.kernel.org', Country='US', FromHeader='org', MailFrom='org' X-Spam-charsets: plain='iso-8859-1' X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: SRS0=C9he=GQ=gmail.com=htejun@kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=arctest; t=1522076078; b=omo+tz1D0SYwqj3mYdIBqKrJeCR+/L67BFXhL4KBjSsK2N/ ctjV7z07N5ytNWrn4CRoIWew07LSyMNbvTcmi+IBfGKssM6fqBvR7R6Ezx2uoKOL dNoi8PLK+bYCc9kjBEfMx6UQcsmVGXG+bODYtN1mmE0sJZzwqNrofOA2ycSXB0B0 Tfx1CQcCY+JIUQZ/Wwx3y6Yp6867PaotXn6jGdT55+Sjuns8NZweZU/lTTQBRKku zt2noJz0xuNXKhv2PHFgdiZPQLKEmEufSwfmcfDdkvttdkIePk5wGHD90Kpb2guH VhnVErAFtulU2ItRynltNGG2cFVGVYqPg/iIV6g== ARC-Message-Signature: i=1; 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dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=htejun@gmail.com X-Google-Smtp-Source: AG47ELvZFYOyGxnFtJgQulKl/ZWJxXzFSf4FP9A1K279EtX1FR3niHh0+Hrx7FAopMvA3KWmPO/gkg== Sender: Tejun Heo Date: Mon, 26 Mar 2018 07:54:31 -0700 From: Tejun Heo To: Andrew Morton Cc: security@kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, linux-mm@kvack.org, torvalds@linux-foundation.org, jannh@google.com, paulmck@linux.vnet.ibm.com, bcrl@kvack.org, viro@zeniv.linux.org.uk, kent.overstreet@gmail.com Subject: Re: [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup Message-ID: <20180326145431.GC1840639@devbig577.frc2.facebook.com> References: <20180314194205.1651587-1-tj@kernel.org> <20180314194515.1661824-1-tj@kernel.org> <20180314194515.1661824-4-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180314194515.1661824-4-tj@kernel.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Hello, Andrew. Do you mind picking up the following patch? I can't find a good tree to route this through. The raw patch can be found at https://marc.info/?l=linux-mm&m=152105674112496&q=raw Thank you very much. On Wed, Mar 14, 2018 at 12:45:11PM -0700, Tejun Heo wrote: > hmm_devmem_find() requires rcu_read_lock_held() but there's nothing > which actually uses the RCU protection. The only caller is > hmm_devmem_pages_create() which already grabs the mutex and does > superflous rcu_read_lock/unlock() around the function. > > This doesn't add anything and just adds to confusion. Remove the RCU > protection and open-code the radix tree lookup. If this needs to > become more sophisticated in the future, let's add them back when > necessary. > > Signed-off-by: Tejun Heo > Reviewed-by: Jérôme Glisse > Cc: linux-mm@kvack.org > Cc: Linus Torvalds > --- > Hello, > > Jérôme, how do you want to route this patch? If you prefer, I can > route it together with other patches. > > Thanks. > > mm/hmm.c | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) > > diff --git a/mm/hmm.c b/mm/hmm.c > index 320545b98..d4627c5 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -845,13 +845,6 @@ static void hmm_devmem_release(struct device *dev, void *data) > hmm_devmem_radix_release(resource); > } > > -static struct hmm_devmem *hmm_devmem_find(resource_size_t phys) > -{ > - WARN_ON_ONCE(!rcu_read_lock_held()); > - > - return radix_tree_lookup(&hmm_devmem_radix, phys >> PA_SECTION_SHIFT); > -} > - > static int hmm_devmem_pages_create(struct hmm_devmem *devmem) > { > resource_size_t key, align_start, align_size, align_end; > @@ -892,9 +885,8 @@ static int hmm_devmem_pages_create(struct hmm_devmem *devmem) > for (key = align_start; key <= align_end; key += PA_SECTION_SIZE) { > struct hmm_devmem *dup; > > - rcu_read_lock(); > - dup = hmm_devmem_find(key); > - rcu_read_unlock(); > + dup = radix_tree_lookup(&hmm_devmem_radix, > + key >> PA_SECTION_SHIFT); > if (dup) { > dev_err(device, "%s: collides with mapping for %s\n", > __func__, dev_name(dup->device)); > -- > 2.9.5 > -- tejun