From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-961214-1520359195-2-10887068363962192998 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, HEADER_FROM_DIFFERENT_DOMAINS 0.249, ME_NOAUTH 0.01, 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='com', 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=mX/F=F4=redhat.com=jglisse@kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=arctest; t=1520359194; b=i6uAYqg/Y+hRzUN+JhbEEdKzmeF/0D4HyhOgkuDWoPpAgX5 LnFTNUnFPjKV71j2oa+S+P/ECeLEXH608zFvmm6cBb87dJOZIHc03PXm9S6JshxC EkVsR/mPgM3yAFOW+fWrMIrn6yD3lVQKdH5BSN8+iT3qRwv+6QiccY418ea79jfc HwdwiDvRVM7jLwTXxY01FkH+0aUthke5FK7de0DdtzbPV6qBRXYgSXkgn+jApsfK UaQygxFjv1Zr3ba7c4069/lV77ZUNdi3mkn1+sTaOTMBCVB+4Hz9oEjJuq6XVfCp yTTzcgpQgvtC7TuJGTpEEJVti4dOcx6jLLgoIvw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=date:from:to:cc:subject:message-id :references:mime-version:content-type:content-transfer-encoding :in-reply-to; s=arctest; t=1520359194; bh=66+c/J2hyZsgCVcaPwZvos C7BYopPFsw9vVhK11Vysw=; b=dLG1T5yFCIkysg7XjoIcVfhq/fg+JuxWuMOqEQ SmIxmezcj8d0whfevxF9AQL9PkiUsG9/bUjGcIzDo2oJTVDM9wU8ORpPGzOrxKjX NqUhTnFbhl2QaAqr8FSDEF1fF78/V4u0Vms7ADa0zGOa7QTXvVaSejob9I6QSmIf ynTLMxgYF0Ja9P6CufyBoChF+ncFPFuIdZ/SbP/xdR2GNbYh7nM/+R6zbebTZM1R ZNIkmuLfl32zSNFBCNCLR+N0Czp2sdh9j9i3XCWJUeFNh2k8kZfdjPrbO8ZSuNpa aHnRHqz9n0vWo4jZSjIx5/Hm64MoWXgz7yQcITi5dZov6kLA== ARC-Authentication-Results: i=1; mx5.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=fail (p=none,d=none) header.from=redhat.com; iprev=pass policy.iprev=198.145.29.99 (mail.kernel.org); spf=none smtp.mailfrom=SRS0=mX/F=F4=redhat.com=jglisse@kernel.org smtp.helo=mail.kernel.org; x-aligned-from=fail; x-category=clean score=0 state=0; x-ptr=pass x-ptr-helo=mail.kernel.org x-ptr-lookup=mail.kernel.org; x-return-mx=pass smtp.domain=kernel.org smtp.result=pass smtp_is_org_domain=yes header.domain=redhat.com header.result=pass header_is_org_domain=yes; x-tls=pass version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128 Authentication-Results: mx5.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=fail (p=none,d=none) header.from=redhat.com; iprev=pass policy.iprev=198.145.29.99 (mail.kernel.org); spf=none smtp.mailfrom=SRS0=mX/F=F4=redhat.com=jglisse@kernel.org smtp.helo=mail.kernel.org; x-aligned-from=fail; x-category=clean score=0 state=0; x-ptr=pass x-ptr-helo=mail.kernel.org x-ptr-lookup=mail.kernel.org; x-return-mx=pass smtp.domain=kernel.org smtp.result=pass smtp_is_org_domain=yes header.domain=redhat.com header.result=pass header_is_org_domain=yes; x-tls=pass version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128 X-Remote-Delivered-To: security@kernel.org DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 148CD21777 Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=jglisse@redhat.com Date: Tue, 6 Mar 2018 12:59:48 -0500 From: Jerome Glisse To: Tejun Heo Cc: torvalds@linux-foundation.org, jannh@google.com, paulmck@linux.vnet.ibm.com, bcrl@kvack.org, viro@zeniv.linux.org.uk, kent.overstreet@gmail.com, security@kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, linux-mm@kvack.org Subject: Re: [PATCH 4/7] HMM: Remove superflous RCU protection around radix tree lookup Message-ID: <20180306175948.GA4791@redhat.com> References: <20180306172657.3060270-1-tj@kernel.org> <20180306173316.3088458-1-tj@kernel.org> <20180306173316.3088458-4-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: <20180306173316.3088458-4-tj@kernel.org> User-Agent: Mutt/1.9.2 (2017-12-15) X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Tue, Mar 06, 2018 at 09:33:13AM -0800, 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. > > This came up while auditing percpu_ref users for missing explicit RCU > grace periods. HMM doesn't seem to depend on RCU protection at all, > so I thought it'd be better to remove it for now. It's only compile > tested. Good catch some left over of old logic. I have more cleanup queued up now that i am about to post nouveau patches to use all this. Thanks for fixing this. > > 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 >