From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELtWvbcbm+qek+9pwgmjFK1wjZ72TSlQ89pRXry/7CcGYT7ITzUbEXjvHyj+qSwys1nYCz0r ARC-Seal: i=1; a=rsa-sha256; t=1521484257; cv=none; d=google.com; s=arc-20160816; b=u51ryyS+P2Qxo2yYquXmO4GBfvP2C4mDb2tqroDC8ZBIr6+LlkoPY5vdiKMhFuQ+jU NaoICppV4A7ysyYPxndTpdKU16/ePK+nz9u30jaWzGmxft1dziOPo3+GKr7DmDJSByDO dcvo18ipFxwjjpLHwdE6xhr6p/uR/UjbWdaNBEimH2sJkD/ts1wBzUJN9ueDX8JFOMQu 6LJXPV0wI2FXYxjBmSv89lqrv3zOgnLqpRu8g34uFXfX1wqLnfF5ytncymWovnH2nlpF y60lWry32YoxMfLfoslmivV4hD86PuxdtxPZLnpJ7N+BSoXkYcblaIBp95cfaYWQrKV2 7kDA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:user-agent:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=7aKn6AMJzX80FyHNG5nWTpVnWwkklnobAseqq6adDHc=; b=F3cQjY4NLy7NZW6sYjwXilBZNwe93d3XfLfME4xcbtbEmF3p/AM9O+HzYYHPvt8pHq EQk/WBsENZzfdLpNzCY93PEMb109RQc/uroj0PN1dTLNZAN3NEXocY6w6bKXn9+Iqpod VVdlnki7UHAVopQrdKBMQIq0+DAO3mpjxYmesrsHRncVZpoG6hbEh83DUpkgGrj+mjTB GrbrZ1v4UO+L1mrNQ7mT6KN/9wFBFhN5TbbaQelXJMhIo7R+Qzt66sjR2nUcQFGLPIac pUpxhiUpvtNhC0LXJpKvWNKmYgmaNkEMUd9ZckZV7fmycEgHAudvySMGEYVcUWqnV8OW zT4A== ARC-Authentication-Results: i=1; mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org 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 4.14 28/41] RDMAVT: Fix synchronization around percpu_ref Date: Mon, 19 Mar 2018 19:08:28 +0100 Message-Id: <20180319180734.083478211@linuxfoundation.org> X-Mailer: git-send-email 2.16.2 In-Reply-To: <20180319180732.195217948@linuxfoundation.org> References: <20180319180732.195217948@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcU2VudCI=?= X-GMAIL-THRID: =?utf-8?q?1595391876679897241?= X-GMAIL-MSGID: =?utf-8?q?1595391876679897241?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.14-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,