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 X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 58C47C63798 for ; Fri, 27 Nov 2020 04:53:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0ED072222F for ; Fri, 27 Nov 2020 04:53:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="v/wxUnB+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404648AbgK0Ex0 (ORCPT ); Thu, 26 Nov 2020 23:53:26 -0500 Received: from z5.mailgun.us ([104.130.96.5]:35173 "EHLO z5.mailgun.us" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731606AbgK0Ex0 (ORCPT ); Thu, 26 Nov 2020 23:53:26 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1606452804; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: MIME-Version: Date: Message-ID: From: References: Cc: To: Subject: Sender; bh=xM24JflFy1SAsCAGU2vOf/vt49oiaZncEUPC7LPr8h0=; b=v/wxUnB+WpGXqFamh7n04VBJWtBuh9KDmMoEpRyg5EaqUhthJwa37USPOJtxR0PYJ3uQF1kG HfMEZEB/SAbt6wRwOYimffXcr2RcGYb2R/WMMhicpB6TVDdcggQcwNlI+UVoqpcYaYh3NshZ oRokKwrHAaeHu0wfe7jFbGCxfdw= X-Mailgun-Sending-Ip: 104.130.96.5 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n09.prod.us-east-1.postgun.com with SMTP id 5fc0863e4146c5eefdbfe31a (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Fri, 27 Nov 2020 04:53:18 GMT Sender: neeraju=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id C2E33C43468; Fri, 27 Nov 2020 04:53:17 +0000 (UTC) Received: from [192.168.0.105] (unknown [49.206.49.183]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: neeraju) by smtp.codeaurora.org (Postfix) with ESMTPSA id 4BE12C433ED; Fri, 27 Nov 2020 04:53:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 4BE12C433ED Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=fail smtp.mailfrom=neeraju@codeaurora.org Subject: Re: [PATCH v2 tip/core/rcu 5/6] srcu: Provide polling interfaces for Tree SRCU grace periods To: paulmck@kernel.org, rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, kent.overstreet@gmail.com References: <@@@> <20201121005919.17152-5-paulmck@kernel.org> From: Neeraj Upadhyay Message-ID: <05712100-9f65-d81c-1eb0-671bc54f3baa@codeaurora.org> Date: Fri, 27 Nov 2020 10:22:59 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20201121005919.17152-5-paulmck@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/21/2020 6:29 AM, paulmck@kernel.org wrote: > From: "Paul E. McKenney" > > There is a need for a polling interface for SRCU grace > periods, so this commit supplies get_state_synchronize_srcu(), > start_poll_synchronize_srcu(), and poll_state_synchronize_srcu() for this > purpose. The first can be used if future grace periods are inevitable > (perhaps due to a later call_srcu() invocation), the second if future > grace periods might not otherwise happen, and the third to check if a > grace period has elapsed since the corresponding call to either of the > first two. > > As with get_state_synchronize_rcu() and cond_synchronize_rcu(), > the return value from either get_state_synchronize_srcu() or > start_poll_synchronize_srcu() must be passed in to a later call to > poll_state_synchronize_srcu(). > > Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/ > Reported-by: Kent Overstreet > [ paulmck: Add EXPORT_SYMBOL_GPL() per kernel test robot feedback. ] > [ paulmck: Apply feedback from Neeraj Upadhyay. ] > Link: https://lore.kernel.org/lkml/20201117004017.GA7444@paulmck-ThinkPad-P72/ > Signed-off-by: Paul E. McKenney > --- For version in -rcu dev Reviewed-by: Neeraj Upadhyay Thanks Neeraj > kernel/rcu/srcutiny.c | 2 +- > kernel/rcu/srcutree.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++--- > 2 files changed, 64 insertions(+), 5 deletions(-) > > diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c > index b073175..c8f4202 100644 > --- a/kernel/rcu/srcutiny.c > +++ b/kernel/rcu/srcutiny.c > @@ -148,7 +148,7 @@ void srcu_drive_gp(struct work_struct *wp) > * straighten that out. > */ > WRITE_ONCE(ssp->srcu_gp_running, false); > - if (USHORT_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) > + if (USHORT_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) > schedule_work(&ssp->srcu_work); > } > EXPORT_SYMBOL_GPL(srcu_drive_gp); > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > index d930ece..945c047 100644 > --- a/kernel/rcu/srcutree.c > +++ b/kernel/rcu/srcutree.c > @@ -810,7 +810,8 @@ static void srcu_leak_callback(struct rcu_head *rhp) > /* > * Start an SRCU grace period, and also queue the callback if non-NULL. > */ > -static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rhp, bool do_norm) > +static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, > + struct rcu_head *rhp, bool do_norm) > { > unsigned long flags; > int idx; > @@ -819,10 +820,12 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh > unsigned long s; > struct srcu_data *sdp; > > + check_init_srcu_struct(ssp); > idx = srcu_read_lock(ssp); > sdp = raw_cpu_ptr(ssp->sda); > spin_lock_irqsave_rcu_node(sdp, flags); > - rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp); > + if (rhp) > + rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp); > rcu_segcblist_advance(&sdp->srcu_cblist, > rcu_seq_current(&ssp->srcu_gp_seq)); > s = rcu_seq_snap(&ssp->srcu_gp_seq); > @@ -841,6 +844,7 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh > else if (needexp) > srcu_funnel_exp_start(ssp, sdp->mynode, s); > srcu_read_unlock(ssp, idx); > + return s; > } > > /* > @@ -874,7 +878,6 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh > static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, > rcu_callback_t func, bool do_norm) > { > - check_init_srcu_struct(ssp); > if (debug_rcu_head_queue(rhp)) { > /* Probable double call_srcu(), so leak the callback. */ > WRITE_ONCE(rhp->func, srcu_leak_callback); > @@ -882,7 +885,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, > return; > } > rhp->func = func; > - srcu_gp_start_if_needed(ssp, rhp, do_norm); > + (void)srcu_gp_start_if_needed(ssp, rhp, do_norm); > } > > /** > @@ -1011,6 +1014,62 @@ void synchronize_srcu(struct srcu_struct *ssp) > } > EXPORT_SYMBOL_GPL(synchronize_srcu); > > +/** > + * get_state_synchronize_srcu - Provide an end-of-grace-period cookie > + * @ssp: srcu_struct to provide cookie for. > + * > + * This function returns a cookie that can be passed to > + * poll_state_synchronize_srcu(), which will return true if a full grace > + * period has elapsed in the meantime. It is the caller's responsibility > + * to make sure that grace period happens, for example, by invoking > + * call_srcu() after return from get_state_synchronize_srcu(). > + */ > +unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp) > +{ > + // Any prior manipulation of SRCU-protected data must happen > + // before the load from ->srcu_gp_seq. > + smp_mb(); > + return rcu_seq_snap(&ssp->srcu_gp_seq); > +} > +EXPORT_SYMBOL_GPL(get_state_synchronize_srcu); > + > +/** > + * start_poll_synchronize_srcu - Provide cookie and start grace period > + * @ssp: srcu_struct to provide cookie for. > + * > + * This function returns a cookie that can be passed to > + * poll_state_synchronize_srcu(), which will return true if a full grace > + * period has elapsed in the meantime. Unlike get_state_synchronize_srcu(), > + * this function also ensures that any needed SRCU grace period will be > + * started. This convenience does come at a cost in terms of CPU overhead. > + */ > +unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp) > +{ > + return srcu_gp_start_if_needed(ssp, NULL, true); > +} > +EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); > + > +/** > + * poll_state_synchronize_srcu - Has cookie's grace period ended? > + * @ssp: srcu_struct to provide cookie for. > + * @cookie: Return value from get_state_synchronize_srcu() or start_poll_synchronize_srcu(). > + * > + * This function takes the cookie that was returned from either > + * get_state_synchronize_srcu() or start_poll_synchronize_srcu(), and > + * returns @true if an SRCU grace period elapsed since the time that the > + * cookie was created. > + */ > +bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) > +{ > + if (!rcu_seq_done(&ssp->srcu_gp_seq, cookie)) > + return false; > + // Ensure that the end of the SRCU grace period happens before > + // any subsequent code that the caller might execute. > + smp_mb(); // ^^^ > + return true; > +} > +EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu); > + > /* > * Callback function for srcu_barrier() use. > */ > -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation