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x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=linuxfoundation.org header.result=pass header_is_org_domain=yes Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031898AbeCSSdM (ORCPT ); Mon, 19 Mar 2018 14:33:12 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:54172 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1032179AbeCSSdK (ORCPT ); Mon, 19 Mar 2018 14:33:10 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tejun Heo , Dennis Dalessandro , Mike Marciniszyn , linux-rdma@vger.kernel.org, Linus Torvalds Subject: [PATCH 4.15 28/52] RDMAVT: Fix synchronization around percpu_ref Date: Mon, 19 Mar 2018 19:08:26 +0100 Message-Id: <20180319180736.648327623@linuxfoundation.org> X-Mailer: git-send-email 2.16.2 In-Reply-To: <20180319180734.976730813@linuxfoundation.org> References: <20180319180734.976730813@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tejun Heo commit 74b44bbe80b4c62113ac1501482ea1ee40eb9d67 upstream. rvt_mregion uses percpu_ref for reference counting and RCU to protect accesses from lkey_table. When a rvt_mregion needs to be freed, it first gets unregistered from lkey_table and then rvt_check_refs() is called to wait for in-flight usages before the rvt_mregion is freed. rvt_check_refs() seems to have a couple issues. * It has a fast exit path which tests percpu_ref_is_zero(). However, a percpu_ref reading zero doesn't mean that the object can be released. In fact, the ->release() callback might not even have started executing yet. Proceeding with freeing can lead to use-after-free. * lkey_table is RCU protected but there is no RCU grace period in the free path. percpu_ref uses RCU internally but it's sched-RCU whose grace periods are different from regular RCU. Also, it generally isn't a good idea to depend on internal behaviors like this. To address the above issues, this patch removes the fast exit and adds an explicit synchronize_rcu(). Signed-off-by: Tejun Heo Acked-by: Dennis Dalessandro Cc: Mike Marciniszyn Cc: linux-rdma@vger.kernel.org Cc: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- drivers/infiniband/sw/rdmavt/mr.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) --- a/drivers/infiniband/sw/rdmavt/mr.c +++ b/drivers/infiniband/sw/rdmavt/mr.c @@ -489,11 +489,13 @@ static int rvt_check_refs(struct rvt_mre unsigned long timeout; struct rvt_dev_info *rdi = ib_to_rvt(mr->pd->device); - if (percpu_ref_is_zero(&mr->refcount)) - return 0; - /* avoid dma mr */ - if (mr->lkey) + if (mr->lkey) { + /* avoid dma mr */ rvt_dereg_clean_qps(mr); + /* @mr was indexed on rcu protected @lkey_table */ + synchronize_rcu(); + } + timeout = wait_for_completion_timeout(&mr->comp, 5 * HZ); if (!timeout) { rvt_pr_err(rdi,