From patchwork Tue Dec 12 17:48:17 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Neeraj upadhyay X-Patchwork-Id: 13489745 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Hovtu6L6" Received: from mail-pl1-x635.google.com (mail-pl1-x635.google.com [IPv6:2607:f8b0:4864:20::635]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4385EAB; Tue, 12 Dec 2023 09:48:54 -0800 (PST) Received: by mail-pl1-x635.google.com with SMTP id d9443c01a7336-1d0897e99e0so34892675ad.3; Tue, 12 Dec 2023 09:48:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1702403333; x=1703008133; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=btFMgkxywo8icROu0D3fMxutyCln5kSOeODGB3sFA/8=; b=Hovtu6L6rdxL/dcstSbje1s3PDnyAtd5s5WHkRMQXIWgA6OvB9ayCArB+fABzzQakX sxkfYNaEELD8X/rWfRIoTEAvNJx1iL3lq4QqcXSZG8z09TIuB73Uf+KxP4CPto/Vw4EQ 4gEDKWOKwKoDBKuiG+y4+bO3Q56gib+kW7cAwDGAKCsWKNLyrdAccjzVIGfKKJElot31 UxnyEmuLhCiuBlQ/hh81n0c8DMIk6h3wy5ZGQjpuRhv0zmB4KlvwYY0fGCBJNi3iYnQc ve6T7nSZDYVh9nnpQRv/F5J155+6Kcxh31RCJj8ymDnXKDWcUJm2+AhyTXKraHJoDseo MI3g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1702403333; x=1703008133; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=btFMgkxywo8icROu0D3fMxutyCln5kSOeODGB3sFA/8=; b=c4ytcBcjTSqlOCPrZbWCiqW8wT60XzKY1lMhP9myvFAbpuPhGYZdwtvEbYRuO087vB LxYyMF4o3+pjP9JiB99zBs/XUb/+ArSTEy2N5N/Vxw6XKHEHCJ/2B1XfaksTffddW/xh kSrQivGR5VRQoeDk4fRa50a8cb4tWuYNC9oc7Vgi498aAPfr5YqHFk5RAX7Wlh8l2CuN M4mB3UtHMSAeqAh+jBKjVlwmhZJ0Qfm7OWCL3LfrtLRugpF02RXCu2GB8j5WEmjcYXQ2 Uixey+cSf//LbYWys+lwREBZlQmFcZdcmTseRYrEMUWMSQ3D3JVwEN7UK7hC+Htx8PRq 5IRQ== X-Gm-Message-State: AOJu0Ywv2XfNqAaLVz9yYxvzHYRzxYwrqda1qkzz149xsWtk64CwYfbf kn0xNa+turxcUFr9BPMy1BWjjgHe/A84hXXB X-Google-Smtp-Source: AGHT+IF2FYbKe+vbMhBcMf71PvvDV88AaCRLwzE7NODtKKTCDPRq1ZkcMsRWJcA8R2zUcGXBL5n6zw== X-Received: by 2002:a17:902:efc5:b0:1d0:cc54:85e2 with SMTP id ja5-20020a170902efc500b001d0cc5485e2mr3010887plb.21.1702403333073; Tue, 12 Dec 2023 09:48:53 -0800 (PST) Received: from localhost.localdomain ([101.0.63.152]) by smtp.gmail.com with ESMTPSA id l17-20020a170902eb1100b001d0b42fa98bsm8880871plb.4.2023.12.12.09.48.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 Dec 2023 09:48:52 -0800 (PST) From: "Neeraj Upadhyay (AMD)" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, paulmck@kernel.org, Neeraj.Upadhyay@amd.com, Frederic Weisbecker , Joel Fernandes , Neeraj Upadhyay Subject: [PATCH rcu 3/3] srcu: Explain why callbacks invocations can't run concurrently Date: Tue, 12 Dec 2023 23:18:17 +0530 Message-Id: <20231212174817.11919-3-neeraj.iitr10@gmail.com> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20231212174750.GA11886@neeraj.linux> References: <20231212174750.GA11886@neeraj.linux> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Frederic Weisbecker If an SRCU barrier is queued while callbacks are running and a new callbacks invocator for the same sdp were to run concurrently, the RCU barrier might execute too early. As this requirement is non-obvious, make sure to keep a record. Signed-off-by: Frederic Weisbecker Reviewed-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney Signed-off-by: Neeraj Upadhyay (AMD) --- kernel/rcu/srcutree.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 2bfc8ed1eed2..0351a4e83529 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1715,6 +1715,11 @@ static void srcu_invoke_callbacks(struct work_struct *work) WARN_ON_ONCE(!rcu_segcblist_segempty(&sdp->srcu_cblist, RCU_NEXT_TAIL)); rcu_segcblist_advance(&sdp->srcu_cblist, rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq)); + /* + * Although this function is theoretically re-entrant, concurrent + * callbacks invocation is disallowed to avoid executing an SRCU barrier + * too early. + */ if (sdp->srcu_cblist_invoking || !rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) { spin_unlock_irq_rcu_node(sdp); @@ -1745,6 +1750,7 @@ static void srcu_invoke_callbacks(struct work_struct *work) sdp->srcu_cblist_invoking = false; more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist); spin_unlock_irq_rcu_node(sdp); + /* An SRCU barrier or callbacks from previous nesting work pending */ if (more) srcu_schedule_cbs_sdp(sdp, 0); }