From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BAFAEC433F5 for ; Tue, 22 Mar 2022 12:30:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234870AbiCVMcH (ORCPT ); Tue, 22 Mar 2022 08:32:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60732 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232851AbiCVMcE (ORCPT ); Tue, 22 Mar 2022 08:32:04 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1AB4874DE1; Tue, 22 Mar 2022 05:30:34 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B95E0614BA; Tue, 22 Mar 2022 12:30:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 98175C340EC; Tue, 22 Mar 2022 12:30:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1647952233; bh=8UgqJKeD83b+41XF6fMFtLi8TcWYbvRRK9SI91LW1cQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XDt4sQWbciCLej+F53LbxtOwznRDJXiHwX8xDrGNpy2FeqBhzp8RltICjsB7lpMK0 A6OutEYTGQW/yjcxckDM2YlHZYdazmmJ3rqy983SP6XeE2waaFYRxa8UXg+TCcey2/ xSBtMXlaoMT9O9jLcS3xkeO047HMcQkKfsnG4UGUqpgv+zkLII5mgzmZIoviFHCetJ qcX9Er/uH19nc36w9RrkmNwvyARkrBhsqUxhR+TPV2Aj9IYF7GS4fWo/T8dNiHqunh iyUPG3YGN3sR5MWZSZQEWBHWvCEE67cD1uBVrfIwYr1bQHVLBwpN3kGQnRfVQSWnMY JkHjcM1YR9kFg== Date: Tue, 22 Mar 2022 13:30:29 +0100 From: Frederic Weisbecker To: Zqiang Cc: paulmck@kernel.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 1/2] rcu: Call rcu_nocb_rdp_deoffload() directly after rcuog/op kthreads spawn failed Message-ID: <20220322123029.GC701946@lothringen> References: <20220318080719.1501471-1-qiang1.zhang@intel.com> <20220318080719.1501471-2-qiang1.zhang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220318080719.1501471-2-qiang1.zhang@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 18, 2022 at 04:07:18PM +0800, Zqiang wrote: > @@ -1009,10 +1015,33 @@ static long rcu_nocb_rdp_deoffload(void *arg) > */ > rcu_segcblist_set_flags(cblist, SEGCBLIST_RCU_CORE); > invoke_rcu_core(); > - ret = rdp_offload_toggle(rdp, false, flags); > - swait_event_exclusive(rdp->nocb_state_wq, > - !rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB | > - SEGCBLIST_KTHREAD_GP)); > + wake_gp = rdp_offload_toggle(rdp, false, flags); > + > + mutex_lock(&rdp_gp->nocb_gp_kthread_mutex); > + if (rdp_gp->nocb_gp_kthread) { > + if (wake_gp) > + wake_up_process(rdp_gp->nocb_gp_kthread); > + > + if (rdp->nocb_cb_kthread) { > + condition = SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP; > + } else { > + /* > + *If rcuop kthread spawn failed, direct remove SEGCBLIST_KTHREAD_CB > + *just wait SEGCBLIST_KTHREAD_GP to be cleared. > + */ > + condition = SEGCBLIST_KTHREAD_GP; > + rcu_segcblist_clear_flags(&rdp->cblist, > SEGCBLIST_KTHREAD_CB); You may be running concurrently againt nocb_gp_wait() -> nocb_gp_update_state_deoffloading() -> rcu_segcblist_clear_flags(cblist, SEGCBLIST_KTHREAD_GP) So you need to protect the flags clear with rcu_nocb lock. > + } > + swait_event_exclusive(rdp->nocb_state_wq, > + !rcu_segcblist_test_flags(cblist, condition)); > + } else { > + rcu_nocb_lock_irqsave(rdp, flags); > + rcu_segcblist_clear_flags(&rdp->cblist, > + SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP); > + rcu_nocb_unlock_irqrestore(rdp, flags); Like you're doing here. Thanks!